Showing papers in "European Journal of Applied Physiology in 1995"

Effects of specific versus cross-training on running performance

Abstract: The cross-training (XT) hypothesis suggests that despite the principle of specificity of training, athletes may improve performance in one mode of exercise by training using another mode. To test this hypothesis we studied 30 well-trained individuals (10 men, 20 women) in a randomized longitudinal trail. Subjects were evaluated before and after 8 weeks of enhanced training (+10%/week), accomplished by adding either running (R) or swimming (XT) to baseline running, versus continued baseline running (C). Both R (- 26.4s) and XT (-13.2s) improved time trial (3.2 km) performance, whereas C did not (-5.4s). There were no significant changes during treadmill running in maximum oxygen uptake (VO2peak; -- 0.2, -- 6.0, and + 2.7%), steady state submaximal lzO2 at 2.68m's -1 ( - 1.2, - 3.3 and + 0.2 ml'kg-l-min-1), velocity at gO2pea k ( + 0.05, + 0.25 and + 0.09 m' s -a) or accumulated 02 deficit (+ 11.2, - 6.1 and + 9.4%) in the R, XT or C groups, respec- tively. There was a significant increase in velocity asso- ciated with a blood lactate concentration of 4 mmol- 1-1 in R but not in XT or C ( + 0.32, + 0.07 and + 0.08 m" s- 2). There were significant changes in arm crank l/O2ve~k (+ 5%) and arm crank 1)O2 at 4 mmol" 1-1 ( + 6.4%) in XT. There was no significant changes in arm crank gO2pea k ( -~- 1.3 and - 7.7%) or arm crank 1/O2 at 4 mmol" 1-1 ( + 0.8 and + 0.4%) in R or C, respectively. The data suggest that muscularly non-similar XT may contribute to improved running performance but not to the same degree as increased specific tranining.

Training-induced changes in muscle architecture and specific tension.

Abstract: Five men underwent unilateral resistance training of elbow extensor (triceps brachii) muscles for 16 weeks. Before and after training, muscle layer thickness and fascicle angles of the long head of the triceps muscle were measured in vivo using B-mode ultrasound, and fascicle lengths were estimated. Series anatomical cross-sectional areas (ACSA) of the triceps brachii muscle were measured by magnetic resonance imaging, from which muscle volume (Vm) was determined and physiological cross-sectional area (PCSA) was calculated. Elbow extension strength (isometric; concentric and eccentric at 30, 90 and 180°·s−1) was measured using an isokinetic dynamometer to determine specific tension. Muscle volumes, ACSA, PCSA, muscle layer thickness and fascicle angles increased after training and their relative changes were similar, while muscle and fascicle length did not change. Muscle strength increased at all velocities; however, specific tension decreased after training. Increase in fascicle angles, which would be the result of increasedVm and PCSA, would seem to imply the occurrence of changes in muscle architecture. This might have given a negative effect on the force-generating properties of the muscles.

In vivo achilles tendon loading' during jumping in humans

Abstract: Elastic behaviour of the human tendomuscular system during jumping was investigated by determination of the in vivo Achilles tendon force. A buckle-type transducer was implanted under local anaesthesia around the right Achilles tendon of an adult subject. After calibration, the Achilles tendon force was recorded together with the triceps surae muscle electromyogram activity and high speed filming and ground reaction force during: a maximal vertical jump from a squat position, a maximal vertical jump from an erect standing position with a preliminary counter-movement, and repetitive submaximal hopping on the spot. Jumping heights were 33, 40 and 7 cm in the squat, the counter movement, and the hopping positions, respectively. The peak Achilles tendon force and mechanical work by the calf muscles were 2233 N and 34 J in the squat jump, 1895 N and 27 J in the counter movement jump, and 3786 N and 51 J when hopping. The changes in tendon length were estimated assuming a stiffness constant calculated from the tendon architecture. The percentages of elastic energy stored in the Achilles tendon during jumping were 23 %, t7% and 34% of the total calf muscle work in the squat jump, the counter movement jump, and hopping, respectively.

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

Abstract: To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO2 production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( $$\dot V{\text{O}}_{\text{2}} $$ ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O2 saturation reached a minimum which was sustained for 1–3 min before $$\dot V{\text{O}}_{{\text{2max}}} $$ was reached. The LAT correlated with both the $$\dot V{\text{O}}_{\text{2}} $$ (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O2 desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of $$\dot V{\text{O}}_{{\text{2max}}} $$ , approaching or reaching a minimum saturation at $$\dot V{\text{O}}_{{\text{2max}}} $$ .

A dynamometer for evaluation of dynamic muscle work

Abstract: The validation of a new dynamometer for evaluation of dynamic muscle work is presented. The device was based on a precise measurement of load displacements of any machine using gravitational loads as external resistance. It allowed, through a sensor consisting of an infrared photo interrupter, the calculation of velocity, force and power during concentric, eccentric and stretch-shortening cycle activity. To validate the dynamometer 33 male and female track and field athletes (12 throwers and 21 jumpers) participated in the study. The throwers (4 women and 8 men) were asked to perform half-squat exercises on a slide machine with a load of 100% of the subject's body mass. The day-to-day reproducibility of half-squat exercises gave a correlation coefficient ofr = 0.88, 0.97 and 0.95 for average push-off force (AF), average push-off velocity (AV), and average push-off power (AP) respectively. Comparison of half-squat measurements was performed against jumping and running test evaluation by the jumpers (7 women and 14 men). The interrelationships among the different variables studied demonstrated a strong correlation between AF, AV and AP and sprinting and jumping parameters (r = 0.53−0.97;P < 0.05−0.001). Using values of AF, AV and AP developed in half-squat exercises executed with different loads, ranging from 35% to 210% of the subject's body mass, it was also possible to establish the force-velocity and power-velocity relationships for both male and female jumpers. In any individual case, the maximal error due to the measurement system was calculated to be less than 0.3%, 0.9% and 1.2% for AF, AV, and AP respectively. Given the accuracy of the ergometer, the high reliability found between 2 days of measurements, and the specificity of the results it is suggested that the dynamic dynamometer would be suitable for evaluation of athletes performing specific skills. In addition, because single and multiple joint movements involving appropriate muscle groups can be easily performed, physiological characteristics could be evaluated for both athletic and rehabilitation purposes. Therefore, because of its simplicity of use and application, and its low cost the dynamometer would be suitable for both laboratory and field conditions.

Electromechanical delay in isometric muscle contractions evoked by voluntary, reflex and electrical stimulation

Abstract: Electromechanical delay (EMD) in isometric contractions of knee extensors evoked by voluntary, tendon reflex (TR) and electrical stimulation (ES) was investigated in 21 healthy young subjects. The subject performed voluntary knee extensions with maximum effort (maximal voluntary contraction, MVC), and at 30%, 60% and 80% MVC. Patellar tendon reflexes were evoked with the reflex hammer being dropped from 60°, 75° and 90° positions. In the percutaneous ES evoked contractions, single switches were triggered with pulses of duration 1.0 ms and of intensities 90, 120 and 150 V. Electromyograms of the vastus lateralis and rectus femoris muscles were recorded using surface electrodes. The isometric knee extension force was recorded using a load cell force transducer connected to the subject's lower leg. The major finding of this study was that EMD of the involuntary contractions [e.g. mean 22.1 (SEM 1.32) ms in TR 90°; mean 17.2 (SEM 0.62) ms in ES 150 V] was significantly shorter than that of the voluntary contractions [e.g. mean 38.7 (SEM 1.18) ms in MVC,P < 0.05]. The relationships between EMD, muscle contractile properties and muscle fibre conduction velocity were also investigated. Further study is needed to explain fully the EMD differences found between the voluntary and involuntary contractions.

The role of metabolites in strength training. II. Short versus long isometric contractions.

Abstract: The role of intramuscular metabolite changes in the adaptations following isometric strength training was examined by comparing the effect of short, intermittent contractions (IC) and longer, continuous (CC) contractions. In a parallel study, the changes in phosphate metabolites and pH were examined during the two protocols using whole-body nuclear magnetic resonance spectroscopy (NMRS). Seven subjects trained three time per week for 14 weeks. The right leg was trained using four sets of ten contractions, each lasting 3 s with a 2-s rest period between each contraction and 2 min between each set. The left leg was trained using four 30-s contractions with a 1-min rest period between each. Both protocols involved isometric contractions at 70% of a maximum voluntary isometric contraction (MVC). The MVC, length:tension and force:velocity relationships and cross-sectional area (CSA) of each leg were measured before and after training. The increase in isometric strength was significantly greater (P = 0.041) for the CC leg (median 54.7%; P = 0.022) than for IC (31.5%; P = 0.022). There were no significant differences between the two protocols for changes in the length:tension or force:velocity relationships. There were significant increases in muscle CSA for the CC leg only. NMRS demonstrated that the changes in phosphate metabolites and pH were greater for the CC protocol. These findings suggest that factors related to the greater metabolite changes during CC training results in greater increases in isometric strength and muscle CSA.

Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo.

Abstract: To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (Δ1) according to the increasing dorsiflexion force (ΔF) with a fixed ankle joint. Notably, the Δ1 − ΔF relationship in the tendon was found to be quadratic in nature (ΔF = cΔ12; c=1.48 ∼ 2.24, r=0.985 ∼ 0.992, n=9) as has been reported in the isolated tendon, although the ΔF − Δ1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.

Sodium intake and post-exercise rehydration in man

Abstract: This study examined the effect of the sodium content of drinks on the rehydration process after exercise. Six healthy male volunteers were dehydrated by a mean (SEM) of 1.9(0.0) % of body mass by intermittent cycle exercise in a warm (32°C), humid (54% RH) environment. Subjects exercised on four occasions at weekly intervals with each trial beginning in the morning, 3 h after a standard breakfast. Over a 30-min period beginning 30 min after the end of exercise, subjects ingested one of the four test drinks in a volume equivalent to 1.5 times their body mass loss. Drink composition was constant except for the sodium (and matching anion) content. Sodium content of drinks A, B, C and D was 2, 26, 52 and 100 mmol · l−1, respectively. Treatment order was randomised using a four-way crossover incomplete block design. Blood and urine samples were obtained before exercise, immediately before and after the rehydration period and at 0.5, 1.5, 3.5 and 5.5 h after the end of the rehydration period. Data were analysed by parametric or non-parametric statistical tests as appropriate. The volume of fluid consumed was the same on all trials [2045(45) ml]. From the 1.5-h sample onwards, a significant treatment effect on cumulative urine output was apparent, with the volume excreted being inversely related to the sodium content of the drink consumed. By the end of the trial, subjects were in net negative fluid balance on trials A [by 689(124) ml] and B [by 359(87) ml]; on trials C [−2(79) ml] and D [+98(67) ml], subjects were approximately euhydrated. Cumulative urinary sodium output was higher on treatment D than on the other trials after 5.5 h. Plasma volume was lower after exercise than before; on trials B, C and D, plasma volume was higher than the pre-exercise value from 0.5 h after the end of the rehydration period onwards. On trial A, plasma volume was higher than the pre-exercise value at 3.5 and 5.5 h after the end of the rehydration period. At 1.5 h after the end of the rehydration period, the increase in plasma volume was greater on trials C and D than on trial A. These results suggest that the fraction of the ingested fluid that was retained was directly related to the sodium concentration.

Association between heart rate variability and training response in sedentary middle-aged men

Abstract: The effect of exercise training on heart rate variability (HRV) and improvements in peak oxygen consumption (\(\dot V{\text{O}}_{\text{2}} \)peak) was examined in sedentary middle-aged men. The HRV and absolute and relative\(\dot V{\text{O}}_{\text{2}} \)peak of training (n = 19) and control (n = 15) subjects were assessed before and after a 24-session moderate intensity exercise training programme. Results indicated that with exercise training there was a significantly increased absolute and relative\(\dot V{\text{O}}_{\text{2}} \)peak (P 0.005) in the high HRV group (17% and 20% respectively) compared to the low HRV group (6% and 1% respectively). The groups did not differ in mean age, pretraining oxygen consumption, or resting heart rate. These results would seem to suggest that a short aerobic training programme does not alter HRV in middle-aged men. Individual differences in HRV, however, may be associated with\(\dot V{\text{O}}_{\text{2}} \)peak response to aerobic training.

A review of the control of breathing during exercise

Abstract: During the past 100 years many experimental investigations have been carried out in an attempt to determine the control mechanisms responsible for generating the respiratory responses observed during incremental and constant-load exercise tests. As a result of these investigations a number of different and contradictory control mechanisms have been proposed to be the sole mediators of exercise hyperpnea. However, it is now becoming evident that none of the proposed mechanisms are solely responsible for eliciting the exercise respiratory response. The present-day challenge appears to be one of synthesizing the proposed mechanisms, in order to determine the role that each mechanism has in controlling ventilation during exercise. This review, which has been divided into three primary sections, has been designed to meet this challenge. The aim of the first section is to describe the changes in respiration that occur during constant-load and incremental exercise. The second section briefly introduces the reader to traditional and contemporary control mechanisms that might be responsible for eliciting at least a portion of the exercise ventilatory response during these types of exercise. The third section describes how the traditional and contemporary control mechanisms may interact in a complex fashion to produce the changes in breathing associated with constant-load exercise, and incorporates recent experimental evidence from our laboratory.

The relationship between voluntary electromyogram, endurance time and intensity of effort in isometric handgrip exercise

Abstract: The relationship between relative force, electromyogram (EMG) and time to fatigue was examined in seven male and seven female subjects [mean (SD) age, 21.7 (3.2) years] during isometric handgrip exercise. Subjects performed sustained submaximal contractions of the right handgrip at three different intensities: 30%, 50%, and 75% of the pretrial maximum voluntary contraction (MVC). EMG was sampled in 1-s epochs every 15 s during the contractions, and the integrated EMG (IEMG) values were then normalized to that of the pretrial MVC. As expected, time to fatigue was longest at 30% MVC and shortest at 75% MVC, but women performed consistently longer than men at each of the three intensities [woman vs men; 400.7 (35.8) vs 364.3 (34.4) s, 205.1 (15.6) vs 139.4 (13) s, and 89.9 (11.4) vs 66.4 (6.4) s, for 30%, 50%, and 75% MVC, respectively; P < 0.05)]. IEMG increased in a non-linear fashion over time during each trial, with the magnitude of IEMG being proportional to the intensity of the contraction. At the endurance limit, IEMG was greatest in the 75% MVC trial, however, no IEMG values reached those obtained in the related MVC [30%, 57.2 (6.9)%; 50%, 84.6 (5.7)%; 75%, 92.8 (7.4)%]. In conclusion, endurance time during sustained submaximal isometric handgrip exercise is dependent up on the intensity of the effort, with women having significantly larger endurance times than men. The related increase in IEMG is also proportional to the intensity of effort, however, the factors causing force to fail prior to the final IEMG reaching its predicted maximum remain to be elucidated.

The relative influence of body characteristics on humid heat stress response.

Abstract: De algemeen geaccepteerde stelling dat de lichaamstemperatuur bepaald wordt door de arbeidsbelasting als percentage van het persoonlijk maximum, en dat de zweetproductie bepaald wordt door de absolute arbeidsbelasting blijkt onvoldoende rekening te houden met substantiele invloeden van inter-individuele verschillen.

The haematological, biochemical and immunological profile of athletes suffering from the overtraining syndrome.

Abstract: To help clarify the overtraining syndrome (OTS), a combination of parameters were measured in ten athletes who were suffering from OTS. Blood samples were obtained at rest and a range of haematological, biochemical and immunological tests were carried out on the samples. For each parameter, the mean value for the group was compared to an established normal range amongst age-matched controls. The subjects were also asked to complete a questionnaire to establish the severity of their condition. The data indicated that the debilitating fatigue experienced by the OTS sufferers was not related to any of the blood parameters traditionally associated with chronic exercise stress, since levels were normal in OTS. The only parameter measured which deviated significantly from the normal range for both the sedentary controls and the athletes was the plasma concentration of glutamine. Although the data in this study would suggest that plasma glutamine concentrations represented an objective, measurable difference between OTS subjects and normal controls, it remains to be shown that there is any correlation between glutamine concentrations and other clinical symptoms of OTS such as physical capability.

The role of metabolites in strength training. I. A comparison of eccentric and concentric contractions

Abstract: This study examined the role of high forces versus metabolic cost in the adaptations following strength training. Ten young, healthy male and female subjects trained one leg using concentric (CL) and the other using eccentric (EL) contractions of the quadriceps muscle for 20 weeks. EL used weights which were 35% higher than those used for CL. Isometric strength, and the length:tension and force:velocity relationship of the muscle were measured before and after training. Muscle cross-sectional area (CSA) was measured near the knee and hip using computed tomography. Increases in isometric strength were greater for CL compared to EL, the difference being significant with the knee at 1.57 rad (90 degrees) [mean (SD), 43.7 (19.6)% vs 22.9 (9.8)%, respectively; P = 0.01]. Increases in isokinetic strength tended to be larger for EL, although the differences were not significant. Significant increases in CSA occurred near the hip for both EL and CL. These results suggest that metabolic cost, and not high forces alone, are involved in the stimuli for muscle hypertrophy and strength gains following high-resistance training.

Neuromuscular performance in voluntary bilateral and unilateral contraction and during electrical stimulation in men at different ages.

Abstract: A group of 33 men divided into three different age groups, M30 years (n = 11), M50 years (n = 12) and M70 years (n = 10) volunteered as subjects for examination of their maximal voluntary isometric bilateral and unilateral forces and force-time curves of the knee extensor muscle group as well as electromyogram activity of the vastus lateralis, vastus medialis and rectus femoris muscles of the right and/or left leg contractions. Electrical stimulation (ES) of 50 Hz was also given by two surface tin electrodes for each subject and each leg separately with the maximal tolerable intensity for recording the isometric force evoked. The maximal force produced by the voluntary isometric unilateral knee extension combined with ES was also measured. Maximal voluntary bilateral force of 1142 (SD 82) N in M30 was greater (P < 0.001) and the force of 1094 (SD 228) N in M50 was also greater (P < 0.05) than that of 962 (SD 70) N recorded for M70. The shapes of the isometric force-time curves, especially in absolute values, differed also among the groups so that the force produced during the early positions of the curve were in M30 greater (P < 0.05-0.001) than the force produced M50 and in M70. Neither the maximal voluntary bilateral force per the summed unilateral force nor the average integrated EMG between the bilateral and unilateral conditions differed significantly from each other either in M30, M50 or in M70. The force produced by pure ES was significantly greater in M30 (P < 0.05) than in M50 and M70, but the latter two groups were not significantly different. When ES was combined with the voluntary contractions, the absolute force values declined (P < 0.05-0.001) with increasing age similarly to those forces produced by the voluntary contractions alone. The present results suggest that increasing age results in great decreases both in the maximal voluntary strength and explosive force characteristics of the neuromuscular system but no bilateral deficit may necessarily be observed either in neural activation or in force production in a simple single joint isometric force production task of the knee extensors. The finding that no difference was observed between M50 and M70 in the force caused by ES alone despite the difference in maximal voluntary force indicated that in addition to the well-known age-related peripheral decrease in muscle mass, maximal voluntary neural activation of these muscles may also decrease to some extent contributing in part to the decrease in strength, especially at older ages.

Core temperature thresholds for hyperpnea during passive hyperthermia in humans.

Abstract: Humans have higher ventilation when they are hyperthermic but it is not known whether core temperature thresholds for ventilation exist, nor has a physiological rationale been presented for this response To examine this question, ventilation was studied in relation to core temperatures in humans rendered hyperthermic in a warm bath Seven subjects [mean (SE), 233 (14) years] wearing only shorts and a thick felt hat with ear flaps were immersed to the neck in a bath at 41 (05) degrees C for 25 min Tympanic (Tty), esophageal (Tes), thigh skin and forehead skin temperatures, heart rate, inspired minute ventilation (V1 at body temperature and pressure, saturated), ventilation frequency and oxygen consumption (VO2 at standard temperature and pressure, dry) were recorded at 30-s intervals At immersion V1 briefly increased to 186 (30) lmin-1, returned to about the pre-immersion value, and significantly increased to 193 (30) lmin-1 by the end of immersion VO2 increased significantly from the pre-immersion value of 027 lmin-1 to 067 lmin-1 by the first 05 min of immersion, but then returned to its pre-immersion value Tty increased to 387 (02) degrees C and Tes increased to 390 (02) degrees C by the end of immersion Core temperature thresholds for increases in V1 were evident at 381 degrees C when expressed against Tty and at 385 degrees C when expressed against Tes The results indicated that during body warming core temperature thresholds for V1 are reached and subsequently a hyperpnea was evident, despite VO2 remaining at a resting value(ABSTRACT TRUNCATED AT 250 WORDS)

Water ingestion does not improve 1-h cycling performance in moderate ambient temperatures.

Abstract: Eight endurance-trained cyclists rode as far as possible in 1 h on a stationary cycle simulator in a moderate environment (20°C, 60% relative humidity, 3 m·s−1 wind speed) while randomly receiving either no fluid (NF) or attempting to replace their approximate 1.71 sweat loss measured in a previous 1-h familiarisation performance ride at approximately 85% of peak oxygen uptake with artificially sweetened, coloured water (F). During F, the cyclists drank mean 1.49 (SEM 0.14)1 of which mean 0.27 (SEM 0.08)1 remained in the stomach at the end of exercise and mean 0.20 (SEM 0.05) 1 was urinated after the trial. Thus, only mean 1.02 (SEM 0.12)1 of the ingested fluid was available to replace sweat losses during the 1-h performance ride. That fluid decreased the mean average heart rate from 166 (SEM 3) to 157 (SEM 5) beats·min−1 (P < 0.0001) and reduced the final mean serum [Na−] and osmolalities from 143 (SEM 0.6) to 139 (SEM 0.6) matom·1−1(P < 0.005) and from 294 (SEM 1.7) to 290 (SEM 1.9) mosmol·1−1 (P = 0.05), respectively. Fluid ingestion did not significantly attenuate rises in plasma anti-diuretic hormone and angiotensin concentrations, or decrease the approximate-15% falls in estimated plasma volume in the F and NF trials. Nor did fluid ingestion significantly affect the approximate 1.71 · h−1 sweat rates, the rises in rectal temperature (from 36.6° to 38.3°C) or the ratings of perceived exertion in the two trials. Ingestion of approximately 1.51 of fluid produced an uncomfortable feeling of stomach fullness and reduced the mean distance covered in 1 h from 43.1 (SEM 0.7) to 42.3 (SEM 0.6) km (P < 0.05). Thus, trying to replace more than 1.01·h−1 sweat losses during high-intensity, short duration exercise in a moderate environment would not appear to induce beneficial physiological effects, and may impair exercise performance.

Aerobic and anaerobic contribution to Wingate test performance in sprint and middle-distance runners.

Abstract: We investigated the aerobic and anaerobic contributions to performance during the Wingate test in sprint and middle-distance runners and whether they were related to the peak aerobic and anaerobic performances determined by two commonly used tests: the force-velocity test and an incremental aerobic exercise test. A group of 14 male competitive runners participated: 7 sprinters, aged 20.7 (SEM 1.3) years, competing in 50, 100 and 200-m events and 7 middle-distance runners, aged 20.0 (SEM 1.0) years, competing in 800, 1,000 and 1,500 m-events. The oxygen uptake ( $$\dot V{\text{O}}_{\text{2}} $$ ) was recorded breath-by-breath during the test (30 s) and during the first 20 s of recovery. Blood samples for venous plasma lactate concentrations were drawn at rest before the start of the test and during the 20-min recovery period. During the Wingate test mean power ( $$\dot W$$ ) was determined and three values of mechanical efficiency, one individual and two arbitrary, 16% and 25%, were used to calculate the contributions of work by aerobic ( $$\dot W$$ aer,ind,16%,25%) and anaerobic ( $$\dot W$$ an,ind,16%,25%) processes. Peak anaerobic power ( $$\dot W$$ an,peak) was estimated by the force-velocity test and maximal aerobic energy expenditure ( $$\dot W$$ aer,peak) was determined during an incremental aerobic exercise test. During the Wingate test, the middle-distance runners had a significantly greater $$\dot V{\text{O}}_{\text{2}} $$ than the sprinters (P < 0.001), who had significantly greater venous plasma lactate concentrations (P < 0.001). Moreover, $$\dot W$$ aer,ind,16%,25% were also significantly higher (P < 0.05) in the middle-distance runners [ $$\dot W$$ aer,ind 45 (SEM 4) % vs 28 (SEM 2) %; $$\dot W$$ aer,16% 30 (SEM 3) % vs 19 (SEM 2) %; $$\dot W$$ aer,25% 46 (SEM 3) % vs 29 (SEM 2)%]; $$\dot W$$ an,ind,16%,25% in the sprint runners (P < 0.05) [ $$\dot W$$ an,ind 72 (SEM 3) % vs 55 (SEM 4) %; $$\dot W$$ an,16% 81 (SEM 2) % vs 70 (SEM 3) %; $$\dot W$$ an,25% 71 (SEM 2) % vs 54 (SEM 3) %]. The $$\dot W$$ aer,ind/ $$\dot W$$ aer,peak and $$\dot W$$ × $$\dot W$$ an,ind/ $$\dot W$$ an,peak ratios, however, were not significantly different between the two groups of athletes. These results would indicate that the sprinters and middle-distance runners used preferentially a metabolic system according to their speciality. Nevertheless, under the conditions of its experiment, they seemed to rely on the same percentage of both peak anaerobic and peak aerobic performance for a given exercise task.

Force-length, torque-angle and EMG-joint angle relationships of the human in vivo biceps brachii

Abstract: The relationships of EMG and muscle force with elbow joint angle were investigated for muscle modelling purposes. Eight subjects had their arms fixed in an isometric elbow jig where the biceps brachii was electrically stimulated (30 Hz) and also in maximum voluntary contraction (MVC). Biceps EMG and elbow torque transduced at the wrist were recorded at 0.175 rad intervals through 1.75 rad of elbow extension. The results revealed that while the torque-length relationship displayed the classic inverted “U” pattern in both evoked and MVC conditions, the force-length relationship displayed a monotonically increasing pattern. Analyses of variance of the EMG data showed that there were no significant changes in the EMG amplitudes for the different joint angles during evoked or voluntary contractions. The result also showed that electrical stimulation can effectively isolated the torque-angle and force-length relationships of the biceps brachii and that the myoelectric signal during isometric contraction is uniform regardless of the length of the muscle or the joint angle.

The topography of eccrine sweating in humans during exercise

Abstract: The purpose of this study was to investigate the distribution of steady-state sweating rates (m sw), during stressful exercise and heat exposures. Six men completed 42-min trials: 2-min rest and 40-min cycling at 40% peak power in 36.6° C (relative humidity 46.0%). The m sw, was monitored using ventilated capsules at the forehead, and at three additional sites. Repeat trials allowed monitoring from eleven skin surfaces. Auditory canal temperature (Tac) and 11 skin temperatures were measured. After normalising m sw to the forehead response within subjects, differences in T ac and onset time thresholds, and transient and steady-state m sw were examined. The pooled, lower torso m sw onset [mean 45.5 (SEM 42.0) s] preceded that of the head [mean 126.5 (SEM 34.8) s, P<0.05], but was not significantly different from the legs [mean 66.6 (SEM 25.7) s], upper torso [mean 80.2 (SEM 36.8) s] or arms [mean 108.6 (SEM 31.2) s]. Transient m sw did not differ among regions (P=0.16). Mean, steady-state forehead m sw [3.20 (SEM 0.51) mg · cm−2 · min−1]was not significantly greater than the scapula, forearm, hand, stomach and lower back m sw (in descending order), but was greater than the chest [1.6 (SEM 0.2)], upperarm [1.6 (SEM 0.2)], calf [1.5 (SEM 0.3)] and thigh m sw [1.0 (SEM 0.2), P<0.05 for all comparisons]. The results did not support the caudal-to-rostral sweat onset evident during supine, resting heat stress. Equivalent T ac sweat thresholds existed between sites, while steady-state m sw topography varied among subjects and was not dominated by central regions.

A cross-sectional study of the size and strength of the lower leg muscles during growth

Abstract: The influences of age and sex on the cross-sectional area (CSA) and isometric strength of the ankle dorsiflexors and plantarflexors (PF) were investigated in four age groups of 121 boys and 121 girls aged: 7–9, 10–12, 13–15, and 16–18 years. A single anatomical cross-section was determined at 30% of the distance from the articular cleft between the femur and tibiacondyles by using an ultrasonic apparatus. In both sexes, the increase in age was associated with significant increases in the CSA and strength (ST) of these opposing muscle groups. The sex differences became apparent in the 13–15 year group for CSA and in the 16–18 year group for ST but the differences reduced considerably when CSA and ST were expressed per unit of the second power of the lower leg length (CSA·LL −2) and the product of CSA and the lower leg length (ST·CSA −1·LL −1), respectively. However,CSA·LL −2 of both muscles had a tendency to be increased at and over the age of 10–12 years, and was the highest at 16–18 years, andST·CSA −1·LL −1 of PF showed higher values in the older boys than in the younger. Thus, it appeared that, at least in the reciprocal muscle groups of the ankle joint, the sex differences in muscle CSA and ST during growth could be accounted for by differences in LL and muscle mass, respectively. However, other factors must also be involved to explain completely the age differences in these variables.

Control of the rate of phosphocreatine resynthesis after exercise in trained and untrained human quadriceps muscles

Abstract: We examined the effect of differences in exercise intensity on the time constant (tc) of phosphocreatine (PCr) resynthesis after exercise and the relationships between tc and maximal oxygen uptake (VO2max) in endurance-trained runners (n = 5) and untrained controls (n = 7) (average VO2max = 66.2 and 52.0 ml.min-1.kg-1, respectively). To measure the metabolism of the quadriceps muscle using phosphorus nuclear magnetic resonance spectroscopy, we developed a device which allowed knee extension exercise inside a magnet. All the subjects performed four types of exercise: light, moderate, severe and exhausting. The end-exercise PCr: [PCr+inorganic phosphate (P(i))] ratio decreased significantly with the increase in the exercise intensity (P < 0.01). Although there was little difference in the end-exercise pH, adenosine diphosphate concentration ([ADP]) and the lowest intracellular pH during recovery between light and moderate exercise, significant changes were found at the two higher intensities (P < 0.01). These changes for runners were smaller than those for the controls (P < 0.05). The tc remained constant after light and moderate exercise and then lengthened in proportion to the increase in intensity (P < 0.05). The runners had a lower tc at the same PCr and pH than the controls, particularly at the higher intensity (P < 0.05). There was a significant correlation between tc and [ADP] in light exercise and between tc and both end-exercise PCr and pH in severe and exhausting exercise (P < 0.05). The threshold of changes in pH and tc was a PCr: (PCr+P(i)) ratio of 0.5. There was a significant negative correlation between the VO2max and tc after all levels of exercise (P < 0.05). However, in the controls a significant correlation was found in only light and moderate exercise (P < 0.05). These findings suggest the validity of the use of tc at an end-exercise PCr: (PCr+P(i)) ratio of more than 0.5 as a stable index of muscle oxidative capacity and the correlation between local and general aerobic capacity. Moreover, endurance-trained runners are characterized by the faster PCr resynthesis at the same PCr and intracellular pH.

The effects of long-term low intensity aerobic training and detraining on serum lipid and lipoprotein concentrations in elderly men and women

Abstract: The effects of long-term low intensity aerobic training and detraining on serum lipid and lipoprotein concentrations were examined in 30 elderly men and women. These subjects were randomly divided into two groups. The training group [n=15; 7 men and 8 women; mean age 75.5 (SD 5.6) years] agreed to take part in physical training using a treadmill with an exercise intensity at the blood lactate concentration threshold for 30 min 3–6 times a week for 9 months. The other group [n=15; 7 men and 8 women; mean age 73.7 (SD 4.4) years] did not perform any particular physical training and was followed as the control. Following this training period the high density lipoprotein-cholesterol (HDL-C) had increased significantly (P<0.01) while the total cholesterol (TC) : HDL-C ratio had decreased significantly (P<0.01) in the training group after 9 months but had not changed in the control group. The TC, triglyceride (TG) and low density lipoprotein-cholesterol (LDL-C) had not changed significantly in either group. No significant difference was seen between the groups throughout the period for TC, LDLC or TG. There was, however, a significant correlation between the initial TC:HDL-C ratio and the change in the TC:HDL-C ratio following 3 months of training (P <0.05). After 1 month of detraining in 5 patients, the HDL-C had decreased significantly (P < 0.05) while the TC:HDL-C had increased significantly in the training group (P<0.01). These results suggested that long-term low intensity aerobic training improved the profile of serum lipid and lipoprotein concentrations, while detraining returned the profile to that of the pretraining levels in elderly persons.

Age predicts cardiovascular, but not thermoregulatory, responses to humid heat stress.

Abstract: Cross-section comparisons of the effect of age on physiological responses to heat stress have yielded conflicting results, in part because of the inability to separate chronological age from factors which change in concert with the biological aging process. The present study was designed to examine the relative influence of age on cardiovascular and thermoregulatory responses to low intensity cycle exercise (60 W for 1 h) in a warm humid environment (35 degrees C, 80% relative humidity). Specifically, the relative importance of age compared to other individual characteristics [maximal oxygen uptake (VO2max), physical activity level, anthropometry, and adiposity] was determined by multiple regression analysis in a heterogeneous sample of 56 subjects in which age (20-73 years) and VO2max (1.86-4.44 l.min-1) were not interrelated. Dependent variables (with ranges) included final values of thermoregulatory responses [rectal temperature (Tre, 37.8-39.2 degrees C), calculated heat storage (S, 3.4-8.1 J.g-1), sweat loss (238-847 g.m-2)] and cardiovascular responses [heart rate (HR, 94-176 beats.min-1), forearm blood flow (FBF, 5.3-31.3 ml.100 ml-1.min-1), mean arterial blood pressure (MAP, 68-122 mmHg), and forearm vascular conductance (FVC = FBF.MAP-1, 0.06-0.44 ml.100 ml-1.min-1.mmHg-1). Age had no significant influence on Tre, S, or sweat loss, all of which were closely related to VO2max. On the other hand, HR, MAP, FBF, and FVC were related to both age and VO2max. Anthropometric variables and adiposity had secondary, but statistically significant, effects on MAP, FBF, FVC, and sweat loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximal physical work performance with European standard based fire-protective clothing system and equipment in relation to individual characteristics.

Abstract: Every fire fighter needs to wear fire-protective clothing and a self-contained breathing apparatus (SCBA) several times a year while carrying out various fire-fighting and rescue operations in hazardous work environments. The aim of the present study was to quantify the effects of a multilayer turnout suit designed to fulfil European standard EN 469 used over standardized (Nordic) clothing and with SCBA (total mass 25.9 kg) on maximal physical work performance, and to evaluate the relationship between individual characteristics and power output with the fire-protective clothing system and SCBA. The subjects were 12 healthy firemen aged 26–46 years. The range of their body mass, body fat and maximal oxygen consumption was 69–101 kg, 10–20% and 2.70–5.86 1·min−1, respectively. The maximal tests without (control) and with the fire-protective clothing system and SCBA were carried out on a treadmill in a thermoneutral environment. When compared to the control test, the decrease in the maximal power output in terms of maximal working time and walking speed averaged 25% (P < 0.001) varying from 18% to 34% with the fire-protective clothing system and SCBA. At maximum, no significant differences were found in pulmonary ventilation, absolute oxygen consumption, the respiratory exchange ratio, heart rate, systolic blood pressure, the rate-pressure product, mechanical efficiency, and the rating of perceived exertion between the tests with and without the fire-protective clothing system and SCBA. The reduction of the power output was related to the extra mass of the fire protective clothing and SCBA. In this study, robust build and parameters associated with good anaerobic capacity were the most powerful individual characteristics contributing to the smallest drop in the power output with the fire-protective clothing system and SCBA. All possible means to decrease the mass of both the fire-protective clothing system and SCBA for maintaining the sufficient power output in physically demanding fire-fighting and rescue tasks need to be considered.

Exercise-induced changes in the expression of surface adhesion molecules on circulating granulocytes and lymphocytes subpopulations

Abstract: This study examined the relationship between exercise-induced changes in the concentration of circulating immunocompetent cells and their surface expression of adhesion molecules: L-selectin (CD62L) and threeβ 2-integrins [LFA-1(CD11a/CD18), Mac-1 (CD11b/CD18), and p150/95(CD11c/CD18)]. Eight young male volunteers exercised on a cycle ergometer for 60 min at 60% maximal oxygen uptake. Peripheral blood samples, collected every 30 min throughout exercise and during the 2-h recovery period, were used for flow-cytometric analysis. The experimental results were compared with control data obtained ever 60 min at corresponding times of the nonexercise day. The exercise regimen induced a granulocytosis and a lymphocytosis, mainly due to an elevation of CD8+ and CD16+ cells. During recovery, a further granulocytosis occurred but accompanied by a lymphopenia. The increased CD8+ cell-count during exercise was characterized by a selective mobilization of the CD62L− and CD11ahigh cells, i.e.primed CD8+ cells. A postexercise suppression of CD4+ cell-count was derived only from CD62L+ cells. The CD11b+ and CD11c+ lymphocytes also increased during exercise, largely attributable to an increase in CD16+ cells which co-expressed CD11b and CD11c molecules. The CD62L surface density of granulocytes increased significantly during recovery. This resulted from a selective influx of CD62Lhigh granulocytes into the circulation. There were no significant changes in per-cell density of the threeβ 2-integrins on granulocytes and lymphocytes throughout the experimental period. These results suggest that the cell-surface expression of CD62L (and CD I la) molecules is associated with the differential mobilization of CD8+ cells during exercise, the postexercise suppression of CD4− cell-counts and the granulocytosis following exercise.

Warm underwater water-jet massage improves recovery from intense physical exercise

Abstract: The effects of warm underwater water-jet massage on neuromuscular functioning, selected biochemical parameters (serum creatine kinase, lactic dehydrogenase, serum carbonic anhydrase, myoglobin, urine urea and creatinine) and muscle soreness were studied among 14 junior track and field athletes. Each subject spent, in a randomized order, two identical training weeks engaged in five strength/power training sessions lasting 3 days. The training weeks differed from each other only in respect of underwater water-jet massage treatments. These were used three times (20 min each) during the treatment week and not used during the control week. During the treatment week continuous jumping power decreased and ground contact time increased significantly less (P < 0.05) and serum myoglobin increased more than during the control week. It is suggested that underwater water-jet massage in connection with intense strength/power training increases the release of proteins from muscle tissue into the blood and enhances the maintenance of neuro-muscular performance capacity.

Muscle metabolism during exercise using phosphorus-31 nuclear magnetic resonance spectroscopy in adolescents

Abstract: Very little has been reported on muscle energetics during exercise in adolescents. This is attributable to the difficulty of subjecting children to muscle biopsy. The purpose of this study was to investigate the characteristics of muscle metabolism during exercisein vivo in adolescents by comparing firstly, with adults and secondly, the differences resulting from physical activity using phosphorus-31 nuclear magnetic resonance (31PNMR) spectroscopy. The subjects were boys aged 12 to 15 years, comprising 21 trained boys and 23 control boys, and 6 adults controls. The ratio of phosphocreatine (PCr):(PCr + Pi), where Pi is inorganic phosphate intracellular pH at exhaustion and the time constant of PCr during recovery were measured in all the subjects using31PNMR. Both groups of children showed higher values of PCr:(PCr + Pi) and intracellular pH at exhaustion than did the adult control group (P < 0.01 orP < 0.05). However, no significant differences were found between the trained boys and the control boys with respect to PCr:(PCr + Pi) and intracellular pH at exhaustion. On the other hand, we found the same values for PCr time constant in all groups. This result suggested no differences of the muscle oxidative capacity between children and adults. We concluded that the adolescents, aged 12 to 15 years in both the trained and control groups, had less glycolytic ability during exercise than the adults.

Haematological and acute-phase responses associated with delayed-onset muscle soreness in humans.

Abstract: Delayed-onset muscle soreness following unaccustomed or eccentric exercise is associated with inflammation, tissue necrosis and the release of muscle enzymes (Newham et al. 1983). We have investigated the time course of changes in circulating leucocytes and serum levels of some acute phase reactants, serum creatine kinase activity (CK) and muscle pain after a 40-min bout of bench-stepping exercise in eight healthy untrained subjects. Leg muscle soreness was greatest 2 days after the exercise bout. Peak serum CK values [mean (SD) 540 (502) IU.1-1] occurred 1-7 days post-exercise. Serum C-reactive protein (CRP) was unchanged from pre-exercise levels [7.8 (3.4) mg.1-1] immediately post-exercise [7.9 (2.3) mg.1-1] but rose to a peak of 17.0 (3.9) mg.1-1 1 day post-exercise, thereafter declining to basal levels. Serum levels of iron and zinc fell below pre-exercise levels for 1-3 days post-exercise. Serum albumin, IgG and IgM fell below pre-exercise levels from 1 day post-exercise, reaching minimal values (about 80% of basal levels) at 7 days post-exercise. The exercise did not appear to significantly affect serum levels of alpha-1-antitrypsin and alpha-1-acid glycoprotein. Two and three days after the exercise bout the circulating numbers of total leucocytes, neutrophils, monocytes and basophils fell 15-20% below pre-exercise levels, whereas lymphocytes, eosinophils and platelets were unchanged. The results indicate that a rapid acute phase inflammatory response is initiated within 1 day of a bout of exercise that induces delayed-onset muscle soreness, and that any later tissue necrosis that may occur is not accompanied by further marked changes in acute-phase reactants such as CRP.