Showing papers in "European Journal of Applied Physiology in 1998"

The spring-mass model and the energy cost of treadmill running.

Abstract: During running, the behaviour of the support leg was studied by modelling the runner using an oscillating system composed of a spring (the leg) and of a mass (the body mass). This model was applied to eight middle-distance runners running on a level treadmill at a velocity corresponding to 90% of their maximal aerobic velocity [mean 5.10 (SD 0.33) m · s−1]. Their energy cost of running (C r ), was determined from the measurement of O2 consumption. The work, the stiffness and the resonant frequency of both legs were computed from measurements performed with a kinematic arm. The C r was significantly related to the stiffness (P < 0.05, r = −0.80) and the absolute difference between the resonant frequency and the step frequency (P < 0.05, r = 0.79) computed for the leg producing the highest positive work. Neither of these significant relationships were obtained when analysing data from the other leg probably because of the work asymmetry observed between legs. It was concluded that the spring-mass model is a good approach further to understand mechanisms underlying the interindividual differences in C r .

Achilles tendon loading during walking: application of a novel optic fiber technique.

Abstract: An optic fiber (O 0.5 mm) was utilized for the study of Achilles tendon forces (ATF) in eight volunteers who walked over a 10 m force platform at three speeds (1.1 ± 0.1 m × s−1, 1.5 ± 0.1 m × s−1 and 1.8 ± 0.2 m × s−1). The presented ATF-time curves showed great intersubject variation in magnitudes of the sudden release of force after initial contact and in the peak ATF's (1430 ± 500 N). This intersubject variation in the peak force decreased only by 4% when cross-sectional area of the tendon was considered. Measured ground reaction forces and plantar pressures confirmed that the subjects walked quite normally during recordings. The peak ATF was found to be rather insensitive to speed in contrast to the rate of ATF development which increased 32% ( p < 0.5) from slow to fast walking speed. It is concluded that the optic fiber technique can be applied to study loading of the musculo-tendinous complex during normal locomotion such as walking.

The effects of short-term resistance training on endocrine function in men and women

Abstract: This investigation examined hormonal adaptations to acute resistance exercise and determined whether training adaptations are observed within an 8-week period in untrained men and women The protocol consisted of a 1-week pre-conditioning orientation phase followed by 8 weeks of heavy resistance training Three lower-limb exercises for the quadriceps femoris muscle group (squat, leg press, knee extension) were performed twice a week (Monday and Friday) with every other Wednesday used for maximal dynamic 1 RM strength testing Blood samples were obtained pre-exercise (Pre-Ex), immediately post-exercise (IP), and 5 min post-exercise (5-P) during the first week of training (T-1), after 6 weeks (T-2) and 8 weeks (T-3) of training to determine blood concentrations of whole-blood lactate (LAC), serum total testosterone (TT), sex-hormone binding globulin (SHBG), cortisol (CORT) and growth hormone (GH) Serum TT concentrations were significantly (P < or = 005) higher for men at all time points measured Men did not demonstrate an increase due to exercise until T-2 An increase in pre-exercise concentrations of TT were observed both for men and women at T-2 and T-3 No differences were observed for CORT between men and women; increases in CORT above pre-exercise values were observed for men at all training phases and at T-2 and T-3 for women A reduction in CORT concentrations at rest was observed both in men and women at T-3 Women demonstrated higher pre-exercise GH values than men at all training phases; no changes with training were observed for GH concentrations Exercise-induced increases in GH above pre-exercise values were observed at all phases of training Women demonstrated higher serum concentrations of SHBG at all time points No exercise-induced increases were observed in men over the training period but women increased SHBG with exercise at T-3 SHBG concentrations in women were also significantly higher at T-2 and T-3 when compared to T-1 values Increases in LAC concentrations due to exercise were observed both for men and women for all training phases but no significant differences were observed with training These data illustrate that untrained individuals may exhibit early-phase endocrine adaptations during a resistance training program These hormonal adaptations may influence and help to mediate other adaptations in the nervous system and muscle fibers, which have been shown to be very responsive in the early phase of strength adaptations with resistance training

Electron spin resonance spectroscopic detection of oxygen-centred radicals in human serum following exhaustive exercise.

Abstract: Free radicals or oxidants are continuously produced in the body as a consequence of normal energy metabolism. The concentration of free radicals, together with lipid peroxidation, increases in some tissues as a physiological response to exercise – they have also been implicated in a variety of pathologies. The biochemical measurement of free radicals has relied in the main on the indirect assay of oxidative stress by-products. This study presents the first use of electron spin resonance (ESR) spectroscopy in conjunction with the spin-trapping technique, to measure directly the production of radical species in the venous blood of healthy human volunteers pre- and post-exhaustive aerobic exercise. Evidence is also presented of increased lipid peroxidation and total antioxidant capacity post-exercise.

Changes in performance, muscle metabolites, enzymes and fibre types after short sprint training.

Abstract: In contrast to endurance training, little research has been carried out to investigate the effects of short (<10 s) sprint training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30–80 m at 90–100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance (maximal oxygen consumption; V˙O2 max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 × 40 m sprints, 24 s recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis) were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and V˙O2 max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.

Specific effects of eccentric and concentric training on muscle strength and morphology in humans.

Abstract: The purpose of this study was to compare pure eccentric and concentric isokinetic training with respect to their possible specificity in the adaptation of strength and morphology of the knee extensor muscles Ten moderately trained male physical education students were divided into groups undertaking eccentric (ETG) and concentric (CTG) training They performed 10 weeks of maximal isokinetic (90 degrees x s(-1)) training of the left leg, 4x10 repetitions - three times a week, followed by a second 10-week period of similar training of the right-leg Mean eccentric and concentric peak torques increased by 18% and 2% for ETG and by 10% and 14% for CTG, respectively The highest increase in peak torque occurred in the eccentric 90 degrees x s(-1) test for ETG (35%) whereas in CTG strength gains ranged 8%-15% at velocities equal or lower than the training velocity Significant increases in strength were observed in the untrained contra-lateral leg only at the velocity and mode used in ipsilateral training Cross-sectional area of the quadriceps muscle increased 3%-4% with training in both groups, reaching statistical significance only in ETG No major changes in muscle fibre composition or areas were detected in biopsies from the vastus lateralis muscle for either leg or training group In conclusion, effects of eccentric training on muscle strength appeared to be more mode and speed specific than corresponding concentric training Only minor adaptations in gross muscle morphology indicated that other factors, such as changes in neural activation patterns, were causing the specific training-induced gains in muscle strength

Energetics of swimming at maximal speeds in humans

Abstract: The energy cost per unit of distance (Cs, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (v), Cs was measured dividing steady-state oxygen consumption (V˙O2) by the speed (v, metres per second). At supra-maximal v, Cs was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = Ean+V˙O2maxtp−V˙O2max(1−e−( t p/)), where Ean was the amount of energy (kilojoules) derived from anaerobic sources, V˙O2max litres per second was the maximal oxygen uptake, α (=20.9 kJ · l O2−1) was the energy equivalent of O2, τ (24 s) was the time constant assumed for the attainment of V˙O2max at muscle level at the onset of exercise, and tp (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with tp to an asymptotic value of 0.418 kJ · kg−1 of body mass for tp ≥ 120 s. The lactic acid component of Ean was obtained from the net increase of lactate concentration after exercise (Δ[La]b) assuming that, when Δ[La]b = 1 mmol · l−1 the net amount of metabolic energy released by lactate formation was 0.069 kJ · kg−1. Over the entire range of v, front crawl was the least costly stroke. For example at 1 m · s−1, Cs amounted, on average, to 0.70, 0.84, 0.82 and 0.124 kJ · m−1 in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m · s−1, Cs was 1.23, 1.47, 1.55 and 1.87 kJ · m−1 in the four strokes, respectively. The Cs was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly Cs attained a minimum at the two lowest v to increase exponentially at higher v. The Cs in breaststroke was a linear function of the v, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of v occurring in the non-propulsive phase.

Reduced stretch reflex sensitivity and muscle stiffness after long-lasting stretch-shortening cycle exercise in humans.

Abstract: It has been suggested that during repeated long-term stretch-shortening cycle (SSC) exercise the decreased neuromuscular function may result partly from alterations in stiffness regulation. Therefore, interaction between the short latency stretch-reflex component (M1) and muscle stiffness and their influences on muscle performance were investigated before and after long lasting SSC exercise. The test protocol included various jumps on a sledge ergometer. The interpretation of the sensitivity of the reflex was based on the measurements of the patellar reflexes and the M1 reflex components. The peak muscle stiffness was measured indirectly and calculated as a coefficient of the changes in the Achilles tendon force and the muscle length. The fatigue protocol induced a marked impairment of the neuromuscular function in maximal SSC jumps. This was demonstrated by a 14.1%-17.7% (n.s. - P < 0.001) reduction in the mean eccentric forces and a 17.3%-31.8% (n.s. - P < 0.05) reduction in the corresponding M1 area under the electromyograms. Both of these methods of assessing the short latency reflex response showed a clear deterioration in the sensitivity of the reflex after fatigue (P < 0.05-0.001). This was also the case for the eccentric peak stiffness of the soleus muscle which declined immediately after fatigue by 5.4% to 7.1% (n.s. - P < 0.05) depending on the jump condition. The results observed would suggest that the modulation of neural input to the muscle was at least partly of reflex origin from the contracting muscle, and furthermore, that the reduced muscle stiffness which accompanied the decreased reflex sensitivity could have been partly responsible for the weakened muscle performance due to impaired utilization of elastic energy.

Acute hormonal responses to heavy resistance exercise in younger and older men

Abstract: The purpose of this investigation was to examine the acute responses of several hormones [total and free testosterone (TT and FT, respectively), adrenocorticotropic hormone (ACTH), cortisol (C), growth hormone (GH), and insulin (INS)] to a single bout of heavy resistance exercise (HRE). Eight younger [30-year (30y) group] and nine older [62-year (62y) group] men matched for general physical characteristics and activity levels performed four sets of ten repetitions maximum (RM) squats with 90 s rest between sets. Blood samples were obtained from each subject via an indwelling cannula with a saline lock pre-exercise, immediately post-exercise (IP), and 5, 15 and 30 min post-exercise. Levels of TT, FT, ACTH, C and lactate significantly increased after HRE for both groups. Pre-HRE pairwise differences between groups were noted only for FT, while post-HRE pairwise differences were found for TT, FT, GH, glucose and lactate. Area under the curve analysis showed that the 30y group had a significantly higher magnitude of increase over the entire recovery period (IP, 5, 15, and 30 min post-exercise) for TT, FT, ACTH and GH. Few changes occurred in the INS response with the only change being that the 62y group demonstrated a decrease IP. Lactate remained elevated at 30 min post-HRE. This investigation demonstrates that age-related differences occur in the endocrine response to HRE, and the most striking changes appear evident in the FT response to HRE in physically active young and older men.

Brain temperature and limits on transcranial cooling in humans: quantitative modeling results

Abstract: Selective brain cooling (SBC) of varying strengths has been demonstrated in a number of mammals and appears to play a role in systemic thermoregulation. Although primates lack obvious specialization for SBC, the possibility of brain cooling in humans has been debated for many years. This paper reports on the use of mathematical modeling to explore whether surface cooling can control effectively the temperature of the human cerebrum. The brain was modeled as a hemisphere with a volume of 1.33 1 and overlying layers of cerebrospinal fluid, skull, and scalp. Each component was assigned appropriate dimensions, physical properties and physiological characteristics that were determined from the literature. The effects of blood flow and of thermal conduction were modeled using the steady-state form of the bio-heat equation. Input parameters included core (arterial) temperature: normal (37 degrees C) or hyperthermic (40 degrees C), air temperature: warm (30 degrees C) or hot (40 degrees C), and sweat evaporation rate: 0, 0.25, or 0.50 l x m(-2) x h(-1). The resulting skin temperatures of the model ranged from 31.8 degrees C to 40.2 degrees C, values which are consistent with data obtained from the literature. Cerebral temperatures were generally insensitive to surface conditions (air temperature and evaporation rate), which affected only the most superficial level of the cerebrum (< or =1.5 mm) The remaining parenchymal temperatures were 0.2-0.3 degrees C above arterial temperatures, regardless of surface conditions. This held true even for the worst-case conditions combining core hyperthermia in a hot environment with zero evaporative cooling. Modeling showed that the low surface-to-volume ratio, low tissue conductivity, and high rate of cerebral perfusion combine to minimize the potential impact of surface cooling, whether by transcranial venous flow or by conduction through intervening layers to the skin or mucosal surfaces. The dense capillary network in the brain assures that its temperature closely follows arterial temperature and is controlled through systemic thermoregulation independent of head surface temperature. A review of the literature reveals several independent lines of evidence which support these findings and indicate the absence of functionally significant transcranial venous flow in either direction. Given the fact that humans sometimes work under conditions which produce face and scalp temperatures that are above core temperature, a transcranial thermal link would not necessarily protect the brain, but might instead increase its vulnerability to environmentally induced thermal injury.

Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type

Abstract: Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake V˙O2max, body mass, body surface area (AD),% body fat, and AD/mass coefficient) exercised on a cycle ergometer at a relative (%V˙O2max, REL) or an absolute (60 W) exercise intensity in a cool (CO 21°C, 50% relative humidity), warm humid (WH 35°C, 80%) and a hot dry (HD 45°C, 20%) environment. Rectal temperature (Tre) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The Tre was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with V˙O2max and V˙O2max per kilogram body mass in most climates, Tre was positively correlated with V˙O2max and V˙O2max per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined Tre and not the greater efficiency for heat loss associated with high V˙O2max. Body fatness significantly affected Tre only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, Tre was positively correlated with AD/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable AD/mass coefficient (high in small subjects). The total amount of variance in Tre responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%–58%) the variance explained in Tre differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%–26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions.

Neuromuscular functioning of athletes and non-athletes in the drop jump.

Abstract: In many sports vertical jumping is important. This study compared neuromuscular functioning of the lower extremity muscles together with some kinetic and kinematic parameters before and during ground contact in drop jumps from two heights [0.4 m (DJ40) and 0.8 m (DJ80)] in 7 highly trained triple-jumpers and 11 physically active controls. The triple-jumpers jumped 32% higher in DJ40 and 34% higher in DJ80, had shorter braking and total contact times, and greater average and peak vertical ground reaction forces than the controls. In both drop jumps in the electromyogram pre-activity of the vastus lateralis and gastrocnemius muscles started earlier in the jumpers than in the controls. For the control group the increase in dropping height was associated with a decrease in the propulsion force, and resulted in more extended knee and ankle angles at touch down and more flexed angles at the deepest position than for the jumpers. All angular displacements for DJ80 were larger than for DJ40 in the control group. The triple jumpers and control subjects differed with respect to their neuromuscular functioning in the drop jump exercise and they responded in a different way to the increase in dropping height.

Acute hormone responses to heavy resistance lower and upper extremity exercise in young versus old men

Abstract: Acute hormone responses of growth hormone (GH), total and free testosterone (TT and FT) and cortisol (C) to heavy resistance isometric exercise were examined in ten young men [YM 26.5 (SD 4.8) years] and ten old men [OM 70.0 (SD 3.7) years]. Loading conditions of the same relative intensity were created for the lower and upper extremity actions separately as well as for both of them together – lower extremity exercise (LE; knee extension), upper extremity exercise (UE; bench press extension), and lower and upper extremity exercise (LUE) performed simultaneously in a seated position. Single voluntary maximal isometric actions lasting for 5 s were performed repeatedly for ten repetitions (with a recovery of 5 s) for a total of four sets. The recovery time between the sets was 1 min. Each exercise led to large acute decreases in maximal isometric force in both YM (P < 0.001) and OM (P < 0.001) ranging from 41% to 26% with no significant differences between the groups. Serum GH concentrations increased in both YM (P < 0.05–0.01) and OM (P < 0.05) but the postexercise value in YM during LE was greater (P < 0.05) than for OM. The TT increased (P < 0.01–0.001) in YM in all three exercises, while in OM the increase occurred only during LE (P < 0.01). The exercises led to increases in FT in YM (P < 0.05 for LE and LUE), while in OM the increase occurred only during LUE (P < 0.05). The pre and postexercise FT were greater in YM (P < 0.001) than in OM. No significant changes occurred in C either in YM or in OM. The blood lactate concentrations increased during the exercises in both YM (P < 0.001) and OM (P < 0.05–0.001) but the postexercise values during LE and LUE in YM were greater (P < 0.05) than in OM. The present data would indicate that the responses of GH, TT and FT to heavy resistance isometric exercise are lowered with increasing age. The reduced acute hormone response together with the lowered basal values in FT in the older men compared to the young men may indicate decreased anabolic effects on muscles and may explain in part the loss of muscle mass and strength associated with aging.

Energy cost and running mechanics during a treadmill run to voluntary exhaustion in humans

Abstract: The aim of the present study was to examine the physiological and mechanical factors which may be concerned in the increase in energy cost during running in a fatigued state. A group of 15 trained triathletes ran on a treadmill at velocities corresponding to their personal records over 3000m [mean 4.53 (SD 0.28) m · s−1] until they felt exhausted. The energy cost of running (CR) was quantified from the net O2 uptake and the elevation of blood lactate concentration. Gas exchange was measured over 1 min firstly during the 3rd–4th min and secondly during the last minute of the run. Blood samples were collected before and after the completion of the run. Mechanical changes of the centre of mass were quantified using a kinematic arm. A significant mean increase [6.9 (SD 3.5)%, P < 0.001] in CR from a mean of 4.4 (SD 0.4) J · kg−1 · m−1 to a mean of 4.7 (SD 0.4) J · kg−1 · m−1 was observed. The increase in the O2 demand of the respiratory muscles estimated from the increase in ventilation accounted for a considerable proportion [mean 25.2 (SD 10.4)%] of the increase in CR. A mean increase [17.0 (SD 26.0)%, P < 0.05] in the mechanical cost (CM) from a mean of 2.36 (SD 0.23) J · kg−1 · m−1 to a mean of 2.74 (SD 0.55) J · kg−1 · m−1 was also noted. A significant correlation was found between CR and CM in the non-fatigued state (r = 0.68, P < 0.01), but not in the fatigued state (r = 0.25, NS). Furthermore, no correlations were found between the changes (from non-fatigued to fatigued state) in CR and the changes in CM suggesting that the increase in CR is not solely dependent on the external work done per unit of distance. Since step frequency decreased slightly in the fatigued state, the internal work would have tended to decrease slightly which would not be compatible with an increase in CR. A stepwise regressions showed that the changes in CR were linked (r = 0.77, P < 0.01) to the changes in the variability of step frequency and in the variability of potential cost suggesting that a large proportion of the increase in CR was due to an increase in the step variability. The underlying mechanisms of the relationship between CR and step variability remains unclear.

Cardiorespiratory responses to underwater treadmill walking in healthy females.

Abstract: This study compared the cardiorespiratory responses of eight healthy women (mean age 30.25 years) to submaximal exercise on land (LTm) and water treadmills (WTm) in chest-deep water (Aquaciser). In addition, the effects of two different water temperatures were examined (28 and 36°C). Each exercise test consisted of three consecutive 5-min bouts at 3.5, 4.5 and 5.5 km · h−1. Oxygen consumption (V˙O2) and heart rate (HR), measured using open-circuit spirometry and telemetry, respectively, increased linearly with increasing speed both in water and on land. At 3.5 km · h−1 V˙O2 was similar across procedures [χ = 0.6 (0.05) l · min−1]. At 4.5 and 5.5 km · h−1 V˙O2 was significantly higher in water than on land, but there was no temperature effect (WTm: 0.9 and 1.4, respectively; LTm: 0.8 and 0.9 l · min−1, respectively). HR was significantly higher in WTm at 36°C compared to WTm at 28°C at all speeds, and compared to LTm at 4.5 and 5.5 km · h−1 (P ≤ 0.003). The HR-V˙O2 relationship showed that at a V˙O2 of 0.9 l · min−1, HR was higher in water at 36°C (115 beats · min−1) than either on land (100 beats · min−1) or in water at 28°C (99 beats · min−1). The Borg scale of perceived exertion showed that walking in water at 4.5 and 5.5 km · h−1 was significantly harder than on land (WTm: 11.4 and 14, respectively; LTm: 9.9 and 11, respectively; P ≤ 0.001). These cardiorespiratory changes occurred despite a slower cadence in water (the mean difference at all speeds was 27 steps/min). Thus, walking in chest-deep water yields higher energy costs than walking at similar speeds on land. This data has implications for therapists working in hydrotherapy pools.

Determinants of maximal instantaneous muscle power in women aged 50–75 years

Abstract: The present study aimed at analysing the age-related decline in maximal muscle power (W˙) in 52 sedentary healthy women aged between 50 and 75 years to determine whether force or velocity is the major determinant. Maximal muscle power was estimated from two types of vertical jumps, squatting (SJ) and counter‐movement (CmJ), performed on a force platform. It was obtained by measuring the vertical force (Fopt) applied to the body centre of gravity and calculating the corresponding vertical velocity (\(\)opt). An age-related decline in absolute W˙ was statistically significant in all the conditions examined and in both peak W˙ and average power (\(\)) values. The decrease in \(\)opt was also statistically significant. Also Fopt declined but this reduction was not statistically significant with the exception of the average value in CmJ. Not surprisingly the highest W˙ were obtained in CmJ, and the difference in power production between the two types of jump showed an age-related decrement only in \(\). The main finding of the study was the demonstration that \(\)opt was the critical determinant of the age-related decline in W˙ in healthy elderly women.

Effect of exercise-induced muscle damage on the blood lactate response to incremental exercise in humans.

Abstract: Eccentric muscle actions are known to induce temporary muscle damage, delayed onset muscle soreness (DOMS) and muscle weakness that may persist for several days. The purpose of the present study was to determine whether DOMS-inducing exercise affects blood lactate responses to subsequent incremental dynamic exercise. Physiological and metabolic responses to a standardised incremental exercise task were measured two days after the performance of an eccentric exercise bout or in a control (no prior exercise) condition. Ten healthy recreationally active subjects (9 male, 1 female), aged 20 (SD 1) years performed repeated eccentric muscle actions during 40 min of bench stepping (knee high step; 15 steps · min−1). Two days after the eccentric exercise, while the subjects experienced DOMS, they cycled on a basket loaded cycle ergometer at a starting work rate of 150 W, with increments of 50 W every 2 min until fatigue. The order of the preceding treatments (eccentric exercise or control) was randomised and the treatments were carried out 2 weeks apart. Two days after the eccentric exercise, all subjects reported leg muscle soreness and exhibited elevated levels of plasma creatine kinase activity (P < 0.05). Endurance time and peak V˙O2 during cycling were unaffected by the prior eccentric exercise. Minute volume, respiratory exchange ratio and heart rate responses were similar but venous blood lactate concentration was higher (P < 0.05) during cycling after eccentric exercise compared with the control condition. Peak blood lactate concentration, observed at 2 min post-exercise was also higher [12.6 (SD 1.4) vs 10.9 SD (1.3) mM; P < 0.01]. The higher blood lactate concentration during cycling exercise after prior eccentric exercise may be attributable to an increased rate of glycogenolysis possibly arising from an increased recruitment of Type II muscle fibres. It follows that determination of lactate thresholds for the purpose of fitness assessment in subjects experiencing DOMS is not appropriate.

Muscle metabolism from near infrared spectroscopy during rhythmic handgrip in humans.

Abstract: The rate of metabolism in forearm flexor muscles (MO2) was derived from near-infrared spectroscopy (NIRS-O2) during ischaemia at rest rhythmic handgrip at 15% and 30% of maximal voluntary contraction (MVC), post-exercise muscle ischaemia (PEMI), and recovery in seven subjects. The MO2 was compared with forearm oxygen uptake (VO2) [flow x (oxygen saturation in arnterial blood-oxygen saturation in venous blood, SaO2 - SvO2)], and with the 31P-magnetic resonance spectroscopy-determined ratio of inorganic phosphate to phosphocreatine (P(I):PCr). During ischaemia at rest, the fall in NIRS-O2 was more pronounced [76 (SEM 3) to 3 (SEM 1)%] than in SvO2 [71 (SEM 3) to 59 (SEM 2)%]. During the handgrip, NIRS-O2 was lower at 30% compared to 15% MVC [58 (SEM 3) v.s. 67 (SEM 3)%] while the SvO2 was similar [29 (SEM 3) v.s. 31 (SEM 4)%]. Accordingly, MO2 as well as P(I):PCr increased twofold, while VO2 increased only 30%. During PEMI after 15% and 30% MVC, NIRS-O2 fell to 9 (SEM 1)% and "0", but the use of oxygen by forearm muscles was not reflected in SvO2. During reperfusion after PEMI, the peak NIRS-O2 was lowest after intense exercise, while for SvO2 the reverse was seen. The discrepancies between NIRS-O2 and SvO2, and therefore between the estimates of the metabolic rate, would suggest significant limitations in sampling venous blood which is representative of the flexor muscle capillaries. In support of this contention, SvO2 and venous pH decreased during the first seconds of reperfusion after PEMI. To conclude, NIRS-O2 of forearm flexor muscles closely reflected the exercise intensity and the metabolic rate determined by magnetic resonance spectroscopy but not that rate derived from flow and the arterio-venous oxygen difference.

Changes in the excitability of soleus muscle short latency stretch reflexes during human hopping after 4 weeks of hopping training

Abstract: Changes in the excitability of the human triceps surae muscle short latency stretch reflexes were investigated in six male subjects before and after 4 weeks of progressive two-legged hopping training. During the measurements the subjects performed 2-Hz hopping with: preferred contact time (PCT) and short contact time. The following reflex parameters were examined before and after the training period: the soleus muscle (SOL) Hoffmann-reflex (H-reflex) at rest and during hopping, the short latency electromyogram (EMG) components of the movement induced stretch reflex (MSR) in SOL and medial gastrocnemius muscle (MG), and the EMG amplitude of the SOL and MG tendon reflexes (T-reflexes) elicited at rest. The main results can be summarized as follows: the SOL T-reflex had increased by about 28% (P < 0.05) after training while the MG T-reflex was unchanged; the SOL MSR (always evident) and the MG MSR (when observable) did not change in amplitude with training, and before training the SOL H-reflex in both hopping situations was significantly depressed to about 40% of the reference value at standing rest (P < 0.05). After training the H-reflex during PCT hopping was no longer depressed. As the value of the measured mechanical parameters (the total work rate, joint angular velocity and the ankle joint work rate) was unchanged after training in both hopping situations, the reflex changes observed could not be ascribed to changes in the movement pattern. To explain the observed changes, hypotheses of changes in the excitability of the stretch reflex caused by the training were taken into consideration and discussed.

Effect of speed and precision demands on human shoulder muscle electromyography during a repetitive task

Abstract: Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied during a hand movement task where five points were marked repeatedly with a pencil. Six female subjects performed with three precision demands and at four speeds. Three of the speeds were predefined, while the last speed was performed as fast as possible. The EMG were recorded from 13 shoulder muscles or parts of muscles. Elbow velocity, acceleration and rectified EMG were calculated for each task. The mean elbow velocity and acceleration increased with speed and precision demands. There was an increase in EMG as the speed demand increased for all three precision demands (P < 0.001), and as the precision demand increased for the two highest predefined speed demands (P < 0.05). The combination of a high speed and a high precision demand resulted in the highest EMG. Different EMG levels were attained for the 13 muscles and the supraspinatus muscle always showed the highest normalized EMG. However, analysis of variance showed the same relative increase for all muscles with speed and precision demands. The EMG changes in response to precision demand can only be explained in part by the differences in movement velocity and acceleration, and other factors such as increased co-contraction must also be taken into account.

Heart rate and blood pressure responses to isometric exercise in young and older men

Abstract: The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.

Electromyogram and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in men.

Abstract: In surface electromyogram (EMG) and mechanomyogram (MMG) the electrical and mechanical activities of recruited motor units (MU) are summated. Muscle fatigue influences the electrical and mechanical properties of the active MU. The aim of this study was to evaluate fatigue-induced changes in the electrical and mechanical properties of MU after a short recovery period, using an analysis of force, surface EMG and MMG. In seven subjects the EMG and MMG were recorded from the biceps brachii muscle during sustained isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) a fatiguing exercise. From the time and frequency domain analysis of the signals, the root mean square (rms) and the mean frequency (f¯) of the power spectrum were calculated. The results were that the mean MVC was 412 (SEM 90) N and 304 (SEM 85) N in fresh and fatigued muscle, respectively; during tests 1 and 2 the mean EMG rms increased from 0.403 (SEM 0.07) mV to 0.566 (SEM 0.09) mV and from 0.476 (SEM 0.07) mV to 0.63 (SEM 0.09) mV, respectively; during test 1 the mean MMG rms decreased from 9.4 (SEM 0.8) mV to 5.7 (SEM 0.9) mV; in contrast, during test 2 constantly lower values were observed throughout contraction; during tests 1 and 2 the EMG f¯ declined from 122 (SEM 7) Hz to 74 (SEM 7) Hz and from 106 (SEM 8) Hz to 60 (SEM 7) Hz, respectively; during test 1 the MMG f¯ increased in the first 6 s from 19.3 (SEM 1.4) Hz to 23.9 (SEM 2.9) Hz, falling to 13.9 (SEM 1.3) Hz at the end of contraction; in contrast, during test 2 the MMG f¯ declined continuously from 18.7 (SEM 1) Hz to 12.4 (SEM 0.8) Hz. The lower MVC after the fatiguing exercise and the changes in the EMG parameters confirmed that 10 min after the fatiguing exercise, the mechanical and electrical activities of MU were altered. In addition, the MMG results suggested that after a 10-min recovery, some highly fatigable MU might not be recruitable.

Ventilatory efficiency and exercise tolerance in 101 healthy volunteers.

Abstract: The ventilatory equivalent for CO2 defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16–75 years, measuring ventilation and gas exchange at rest (n = 64) and on exercise (modified Naughton protocol, n = 101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output (V˙ E:V˙CO2), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output (V˙ E vs V˙CO2 slope), oxygen uptake at the anaerobic threshold and at maximum (V˙O2AT,V˙O2max, respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [V˙ E:V˙CO2 50.5 (SD 8.8) vs 57.6 (SD 12.6) P<0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: (V˙ E vs V˙CO2 slope = 0.13 × age + 19.9; women: V˙ E vs V˙CO2 slope = 0.12 × age + 24.4). The V˙O2AT and V˙O2max were 23 (SD 5) and 39 (SD 7) ml O2 · kg · min−1 in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The V˙O2AT was reached at 58 (SD 9)% V˙O2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults.

Adrenal medulla and exercise training.

Abstract: The adrenaline release from the adrenal medulla increases during exercise, but at a given absolute work intensity the magnitude of this response is less pronounced in endurance trained vs sedentary individuals most likely due to a lower sympathetic stimulation of the adrenal medulla. However, when trained and untrained subjects are compared at identical relative work loads as well as in response to numerous non-exercise stimuli. endurance trained athletes have a higher epinephrine secretion capacity compared to sedentary individuals. This indicates a development of a so-called "sports adrenal medulla" as a result of a long term adaptation of an endocrine gland to physical training. Such an adaptation is parallel to adaptations taking place in other tissues like skeletal muscle and the heart. and can be advantageous in relation to both exercise performance in the competing athlete and cause a biological rejuvenation in relation to aging.

Effect of oral creatine ingestion on parameters of the work rate-time relationship and time to exhaustion in high-intensity cycling.

Abstract: The relationship between work rate (W) and time to exhaustion (t) during intense exercise is commonly described by either a hyperbolic function (NLin), t= W'/(W-Wcp), or by its linear equivalent (LinW) Wlim=W' + Wcp(t). The parameter Wcp (critical power) has been described as an inherent characteristic of the aerobic energy system, while W' has been shown to be a ralid estimate of anaerobic work capacity. Recent studies have demonstrated that oral supplementation of creatine monohydrate (CrH2O) increases total muscle creatine stores, and have linked these increases to improved performances in intense intermittent exercise. This study was conducted to determine the effect of CrH2O supplementation on estimates of W' and Wcp derived from the NLin and LinW equations, and to determine the effect of CrH2O on t in exhaustive constant power exercise of different intensities. Fifteen active but untrained university students completed three phases of testing on a cycle ergometer: (1) familiarization, three learning trials, (2) baseline determination of W' and Wcp, four bouts performed at a W selected to elicit fatigue in 90-600 s, and (3) experimental determination of W' and Wcp, four bouts performed at the same W as baseline, but performed after 5 days of ingesting either a placebo (4 x 6 g of glucose/day) or CrH2O (4 x 5 g of CrH2O and 1 g glucose/day). Testing was administered in a double-blind manner. Analyses of covariance revealed a significant effect for CrH2O on both estimates of W' (NLin, P=0.04; LinW, P < 0.01), but not on estimates of Wcp (NLin, P=0.37; LinW; P=0.30). Within groups, t was significantly different for only CrH2O at the two highest Ws (P=0.04). It is concluded that oral ingestion of CrH2O increases estimates of W' due to an improved t at the shorter, more intense exercise bouts.

Chronobiological effects on exercise performance and selected physiological responses.

Abstract: Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours, 1200 hours, 1600 hours, and 2000 hours) within the segment of the 24-h day in which strenuous physical activity is typically performed. Ten physically fit, but untrained, male university students served as subjects. The results revealed that exercise performance was unaffected by chronobiological effects. Similarly, oxygen uptake, minute ventilation and heart rate showed no time of day influences under pre-, submaximal, and maximal exercise conditions. Ratings of perceived exertion were unaffected by time of day effects during submaximal and maximal exercise. In contrast, rectal temperature exhibited a significant chronobiological rhythm under all three conditions. Under pre- and submaximal exercise conditions, significant time of day effects were noted for respiratory exchange ratio, while a significant rhythmicity of blood pressure was evident during maximal exercise. However, none of these physiological variables exhibited significant differential responses (percent change from pre-exercise values) to the exercise stimulus at any of the four time points selected for study. Conversely, resting plasma lactate levels and lactate responses to maximal exercise were found to be significantly sensitive to chronobiological influences. Absolute post-exercise plasma norepinephrine values, and norepinephrine responses to exercise (percent change from pre-exercise values), also fluctuated significantly among the time points studied. In summary, these data suggest that aerobic exercise performance does not vary during the time frame within which exercise is normally conducted, despite the fact that some important physiological responses to exercise do fluctuate within that time period.

Physiological significance of hydrophilic and hydrophobic textile materials during intermittent exercise in humans under the influence of warm ambient temperature with and without wind.

Abstract: The purpose of this present study was to compare the physiological effects of the hydrophilic and hydrophobic properties of the fabrics investigated in exercising and resting subjects at an ambient temperature of 30 degrees C and a relative humidity of 50% with and without wind. Three kinds of clothing ensemble were tested: wool and cotton blend with high moisture regain (A), 100% cotton with intermediate moisture regain (B), 100% polyester clothing with low moisture regain (C). The experiments were performed using seven young adult women as subjects. They comprised six repeated periods of 10-min exercise on a cycle ergometer at an intensity of 40% maximal oxygen uptake followed by 5 min of rest (20 min for the last rest). The experiments comprised two sessions. During session I (first three repetitions of exercise and rest) the subjects were exposed to an indifferent wind velocity and during session II (last three repetitions of exercise and rest) they were exposed to a wind velocity of 1.5 m x s(-1). Rectal temperature and skin temperatures at eight sites, pulse rate and clothing microclimate were recorded throughout the whole period. The main findings can be summarized as follows: rectal temperature during session II was kept at a significantly lower level in A than in B and C. Clothing microclimate humidity at the chest was significantly lower in A than in B and C during session II. Skin and clothing microclimate temperatures at the chest were significantly lower in A than in B and C during session II. Pulse rate was significantly higher in C than in A and B during sessions I and II. It was concluded that the hydrophilic properties of the fabrics studied were of physiological significance for reducing heat strain during exercise and rest especially when influenced by wind.

Adaptations in rat skeletal muscle following long-term resistance exercise training

Abstract: The purpose of this investigation was to determine whether long-term, heavy resistance training would cause adaptations in rat skeletal muscle structure and function. Ten male Wistar rats (3 weeks old) were trained to climb a 40-cm vertical ladder (4 days/week) while carrying progressively heavier loads secured to their tails. After 26 weeks of training the rats were capable of lifting up to 800 g or 140% of their individual body mass for four sets of 12-15 repetitions per session. No difference in body mass was observed between the trained rats and age-matched sedentary control rats. Absolute and relative heart mass were greater in trained rats than control rats. When expressed relative to body mass, the mass of the extensor digitorum longus (EDL) and soleus muscles was greater in trained rats than control rats. No difference in absolute muscle mass or maximum force-producing capacity was evident in either the EDL or soleus muscles after training, although both muscles exhibited an increased resistance to fatigue. Individual fibre hypertrophy was evident in all four skeletal muscles investigated, i.e. EDL, soleus, plantaris and rectus femoris muscles of trained rats, but muscle fibre type proportions within each of the muscles tested remained unchanged. Despite an increased ability of the rats to lift progressively heavier loads, this heavy resistance training model did not induce gross muscle hypertrophy nor did it increase the force-producing capacity of the EDL or soleus muscles.

The effects of intermittent exposure to hypoxia during endurance exercise training on the ventilatory responses to hypoxia and hypercapnia in humans

Abstract: The present study was performed to investigate the effects of a combination of intermittent exposure to hypoxia during exercise training for short periods on ventilatory responses to hypoxia and hypercapnia (HVR and HCVR respectively) in humans. In a hypobaric chamber at a simulated altitude of 4,500 m (barometric pressure 432 mmHg), seven subjects (training group) performed exercise training for 6 consecutive days (30 min · day−1), while six subjects (control group) were inactive during the same period. The HVR, HCVR and maximal oxygen uptake (V˙O2 max) for each subject were measured at sea level before (pre) and after exposure to intermittent hypoxia. The post exposure test was carried out twice, i.e. on the 1st day and 1 week post exposure. It was found that HVR, as an index of peripheral chemosensitivity to hypoxia, was increased significantly (P < 0.05) in the control group after intermittent exposure to hypoxia. In contrast, there was no significant increase in HVR in the training group after exposure. The HCVR in both groups was not changed by intermittent exposure to hypoxia, while V˙O2 max increased significantly in the training group. These results would suggest that endurance training during intermittent exposure to hypoxia depresses the increment of chemosensitivity to hypoxia, and that intermittent exposure to hypoxia in the presence or absence of exercise training does not induce an increase in the chemosensitivity to hypercapnia in humans.

Oxygen uptake does not increase linearly at high power outputs during incremental exercise test in humans.

Abstract: A group of 12 healthy non-smoking men [mean age 22.3 (SD 1.1) years], performed an incremental exercise test. The test started at 30 W, followed by increases in power output (P) of 30 W every 3 min, until exhaustion. Blood samples were taken from an antecubital vein for determination of plasma concentration lactate [La-]pl and acid-base balance variables. Below the lactate threshold (LT) defined in this study as the highest P above which a sustained increase in [La-]pl was observed (at least 0.5 mmol x l[-1] within 3 min), the pulmonary oxygen uptake (VO2) measured breath-by-breath, showed a linear relationship with P. However, at P above LT [in this study 135 (SD 30) W] there was an additional accumulating increase in VO2 above that expected from the increase in P alone. The magnitude of this effect was illustrated by the difference in the final P observed at maximal oxygen uptake (VO2max) during the incremental exercise test (Pmax,obs at VO2max) and the expected power output at VO2max(Pmax,exp at VO2max) predicted from the linear VO2-P relationship derived from the data collected below LT. The Pmax,obs at VO2max amounting to 270 (SD 19) W was 65.1 (SD 35) W (19%) lower (P < 0.01) than the Pmax,exp at VO2max. The mean value of VO2max reached at Pmax,obs amounted to 3555 (SD 226) ml x min(-1) which was 572 (SD 269) ml x min(-1) higher (P < 0.01) than the VO2 expected at this P, calculated from the linear relationship between VO2 and P derived from the data collected below LT. This fall in locomotory efficiency expressed by the additional increase in VO2, amounting to 572 (SD 269) ml O2 x min(-1), was accompanied by a significant increase in [La-]pl amounting to 7.04 (SD 2.2) mmol x l(-1), a significant increase in blood hydrogen ion concentration ([H+]b) to 7.4 (SD 3) nmol x l(-1) and a significant fall in blood bicarbonate concentration to 5.78 (SD 1.7) mmol x l(-1), in relation to the values measured at the P of the LT. We also correlated the individual values of the additional VO2 with the increases (delta) in variables [La-]pl and delta[H+]b. The delta values for [La-]pl and delta[H+]b were expressed as the differences between values reached at the Pmax,obs at VO2max and the values at LT. No significant correlations between the additional VO2 and delta[La-]pl on [H+]b were found. In conclusion, when performing an incremental exercise test, exceeding P corresponding to LT was accompanied by a significant additional increase in VO2 above that expected from the linear relationship between VO2 and P occurring at lower P. However, the magnitude of the additional increase in VO2 did not correlate with the magnitude of the increases in [La-]pl and [H+]b reached in the final stages of the incremental test.