Showing papers in "European Journal of Applied Physiology in 2007"

From space to Earth: advances in human physiology from 20 years of bed rest studies (1986–2006)

Abstract: Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body’s upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10–15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures—exercise (aerobic, resistive, vibration), nutritional and pharmacological—are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.

Endurance training guided individually by daily heart rate variability measurements.

Abstract: Purpose of this study was to test utility of heart rate variability (HRV) in daily endurance exercise prescriptions. Twenty-six healthy, moderately fit males were randomized into predefined training group (TRA, n = 8), HRV-guided training group (HRV, n = 9), and control group (n = 9). Four-week training period consisted of running sessions lasting 40 min each at either low- or high-intensity level. TRA group trained on 6 days a week, with two sessions at low and four at high intensity. Individual training program for HRV group was based on individual changes in high-frequency R-R interval oscillations measured every morning. Increase or no change in HRV resulted in high-intensity training on that day. If there was significant decrease in HRV (below reference value [10-day mean-SD] or decreasing trend for 2 days), low-intensity training or rest was prescribed. Peak oxygen consumption (VO(2peak)) and maximal running velocity (Load(max)) were measured in maximal treadmill test before and after the training. In TRA group, Load(max) increased from 15.1 +/- 1.3 to 15.7 +/- 1.2 km h(-1) (P = 0.004), whereas VO(2peak) did not change significantly (54 +/- 4 pre and 55 +/- 3 ml kg(-1) min(-1) post, P = 0.224). In HRV group, significant increases were observed in both Load(max) (from 15.5 +/- 1.0 to 16.4 +/- 1.0 km h(-1), P < 0.001) and VO(2peak) (from 56 +/- 4 to 60 +/- 5 ml kg(-1) min(-1), P = 0.002). The change in Load(max) was significantly greater in HRV group compared to TRA group (0.5 +/- 0.4 vs. 0.9 +/- 0.2 km h(-1), P = 0.048, adjusted for baseline values). No significant differences were observed in the changes of VO(2peak) between the groups. We concluded that cardiorespiratory fitness can be improved effectively by using HRV for daily training prescription.

Effect of high versus low-velocity resistance training on muscular fitness and functional performance in older men

Abstract: This study investigated the effect of a 10-week power training (PT) program versus traditional resistance training (TRT) on functional performance, and muscular power and strength in older men. Twenty inactive volunteers (60-76 years old) were randomly assigned to a PT group (three 8-10 repetition sets performed as fast a possible at 60% of 1-RM) or a TRT group (three 8-10 repetition sets with 2-3 s contractions at 60% of 1-RM). Both groups exercised 2 days/week with the same work output. Outcomes were measured with the Rikli and Jones functional fitness test and a bench and leg press test of maximal power and strength (1-RM). Significant differences between and within groups were analyzed using a two-way analysis of variance (ANOVA). At 10 weeks there was a significantly (P < 0.05) greater improvement in measures of functional performance in the PT group. Arm curling improved by 50 versus 3% and a 30 s chair-stand improved by 43 versus 6% in the PT and TRT groups, respectively. There was also a significantly greater improvement in muscular power (P < 0.05) in the PT group. The bench press improved by 37 versus 13%, and the leg press by 31 and 8% in the PT and TRT groups, respectively. There was no significant difference between groups in improved muscular strength. It appears that in older men there may be a significantly greater improvement in functional performance and muscular power with PT versus low velocity resistance training.

Resistance exercise-induced increase in muscle mass correlates with p70S6 kinase phosphorylation in human subjects.

Abstract: The purpose of the present study was to investigate the possible relationship between a change in Thr(389) phosphorylation of p70S6 kinase (p70(S6k)) after a single resistance training session and an increase in skeletal muscle mass following short-term resistance training. Eight male subjects performed an initial resistance training session in leg press, six sets of 6RM with 2 min between sets. Muscle biopsies were obtained from the vastus lateralis before (T1) and 30 min after the initial training session (T2). Six of these subjects completed a 14-week resistance-training programme, three times per week (nine exercises, six sets, 6RM). A third muscle biopsy was obtained at the end of the 14-week training period (T3). One repetition maximum (1RM) squat, bench press and leg press strength as well as fat-free mass (FFM, with dual energy X-ray absorptiometry) were determined at T1 and T3. The results show that the increase in Thr(389) phosphorylation of p70(S6k) after the initial training session was closely correlated with the percentage increase in whole body FFM (r = 0.89, P < 0.01), FFM(leg) (r = 0.81, P < 0.05), 1RM squat (r = 0.84, P < 0.05), and type IIA muscle fibre cross sectional area (r = 0.82, P < 0.05) after 14 weeks of resistance training. These results may suggest that p70(S6k) phosphorylation is involved in the signalling events leading to an increase in protein accretion in human skeletal muscle following resistance training, at least during the initial training period.

Differences in quadriceps muscle strength and fatigue between lean and obese subjects

Abstract: The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m²) and ten lean (mean age: 27 years; mean BMI: 23 kg/m²) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180°/s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (−63.5%) than in lean subjects (−50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (−32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle fatigue—at least those associated to the present stimulated test—were not influenced by obesity. The observed quadriceps muscle function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese subjects during daily living activities.

Preferred and optimal stride frequency, stiffness and economy: changes with fatigue during a 1-h high-intensity run.

Abstract: Metabolic cost of submaximal running at constant speed is influenced by various factors including fatigue and kinematic characteristics. Metabolic costs typically drift upwards during extended running while stride characteristics often shift away from initial. When non-fatigued, experienced runners naturally optimize stride frequency in a manner that minimizes oxygen uptake. An initial objective was to determine whether runners demonstrate a similar self-optimizing capability when fatigued where stride characteristics have perhaps shifted away from the initial state. A secondary objective involved measurement of vertical and leg stiffness characteristics as a potential explanation for frequency changes with fatigue. We hypothesized that runners decrease stride frequency and stiffness with fatigue while optimizing these characteristics to minimize metabolic cost. Sixteen experienced runners completed a near maximal effort 1-h treadmill run at a constant speed. Preferred and optimal stride frequencies (PSF and OSF) were measured near the beginning and end of the hour run using frequencies ±4 and ±8% around PSF. From vertical force data recorded throughout the run, leg and vertical stiffness were determined. As expected, oxygen uptake significantly increased during the run from 45.9 to 47.4 ml kg−1 min−1 (P = 0.004). There was no difference between preferred and optimal stride frequencies at the beginning or the end of running (P = 0.978), however both PSF and OSF significantly decreased from 1.45 to 1.43 Hz (P = 0.026). All runners self-optimized stride frequency at the beginning and end of one-hour of running despite changes of optimal stride frequency. Stiffness and stride frequency changes were subject specific with some runners exhibiting little to no change. No clear relationship of frequency or stiffness changes to economy was found.

Monitoring for overreaching in rugby league players.

Abstract: The aim of this study was to identify indicators of non-functional overreaching (NFOR) in team sport athletes undertaking intensive training loads. Eighteen semi-professional rugby league players were randomly assigned into two pair matched groups. One group completed 6 weeks of normal training (NT) whilst the other group was deliberately overreached through intensified training (IT). Both groups then completed the same 7-day stepwise training load reduction taper. Multistage fitness test (MSFT) performance, $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{2\max }} $$ , peak aerobic running velocity (V max), maximal heart rate, vertical jump, 10-s cycle sprint performance and body mass were measured pre- and post-training period and following the taper. Hormonal, haematological and immunological parameters were also measured pre-training and following weeks 2, 4 and 6 of training and post-taper. MANOVA for repeated measures with contrast analysis indicated that MSFT performance and $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{2\max }} $$ were significantly reduced in the IT group over time and condition, indicating that a state of overreaching was attained. However, the only biochemical measure that was significantly different between the IT and NT group was the glutamine to glutamate (Gln/Glu) ratio even though testosterone, testosterone to cortisol (T/C) ratio, plasma glutamate, and CK activity were significantly changed after training in both groups. Positive endurance and power performance changes were observed post-taper in the IT group confirming NFOR. These changes were associated with increases in the T/C ratio and the Gln/Glu ratio and decreases in plasma glutamate and CK activity. These results indicate that although there was no single reliable biochemical marker of NFOR in these athletes, the Gln/Glu ratio and MSFT test may be useful measures for monitoring responses to IT in team sport athletes.

Physical activity patterns assessed by accelerometry in older people.

Abstract: Research into daily physical activity (PA) patterns of older adults (≥70 years) has primarily relied on self-report. This study used accelerometry, an objective measure of minute-by-minute movement, to assess PA volume and intensity performed by older adults recruited to the Better Ageing project. Results were used to estimate the degree to which current health recommendations for PA were met. Participants [91 older females (OF) aged 76.0 ± 4.0 years (mean ± SD), 70 older males (OM) 76.3 ± 3.9 years, 23 young females (YF) 26.8 ± 4.1 years and 22 young males (YM) 27.0 ± 4.2 years] wore an MTI actigraph model 7164 recording activity in 1-min epochs for 7 days. Only those with at least 5 days, and 10 h of actigraph data per day, were included in the analysis, using Caloric.Bas (CSA Inc. 1999) software and a tailored Microsoft Access 2000 macro. Mean counts min-1 day-1 were 37% lower for older adults than for young adults [OF 236.1 ± 84.4 vs. YF 370.0 ± 81.1 counts min-1 day-1 t(114) = −6.86, P < 0.001; OM 255.1 ± 103.0 vs. YM 404.3 ± 134.0 ct min-1 day-1, t(91) = −5.55, P < 0.001]. Older adults were more restricted in activity intensity range performing significantly fewer minutes of moderate to vigorous (MV) PA day-1 than young adults [OF 16.7 ± 12.2 vs. YF 38.4 ± 18.4 MVPA min day-1, t(114) = −6.90, P < 0.001; OM 23.8 ± 20.0 vs. YM 40.4 ± 19.2 MVPA min day-1, t(91) = −3.47, P = 0.001]. Nearly half of older adults did not perform any sustained 10-min MVPA bouts (OF 48.4% vs. YF 13.0%, χ2 = 8.10, P = 0.004; OM 44.3% vs. YM 4.5%, χ 2 = 9.97, P = 0.002), and none met current PA recommendations for health. This study is the first to provide objective data on a large sample of adults aged 70 years and over and indicates low levels of daily movement that are likely to be inadequate for optimal health benefit.

Strength, power output and symmetry of leg muscles: effect of age and history of falling.

Abstract: Risk factors for medically unexplained falls may include reduced muscle power, strength and asymmetry in the lower limbs. Conflicting reports exist about strength and there is little information about power and symmetry. Forty-four healthy young people (29.3 ± 0.6 years), 44 older non-fallers (75.9 ± 0.6 years), and 34 older fallers (76.4 ± 0.8 years) were studied. Isometric, concentric and eccentric strength of the knee and ankle muscles and leg extension power were measured bilaterally. The younger group was stronger in all muscles and types of contraction than both older groups (P < 0.02–0.0001). Strength differences between the older groups occasionally reached significance in individual muscles and types of contraction but overall the fallers had 85% of the strength and 79% of the power of the non-fallers (P < 0.001). Young subjects generated more power than both older groups (P < 0.0001) and the fallers generated less than the non-fallers (P = 0.03). Strength symmetry showed an inconsistent age effect in some muscles and some contraction types. This was similar overall in the two older groups. Both older groups had greater asymmetry in power than the young (P < 0.02–0.004). Power asymmetry tended to be greater in the fallers than the non-fallers but this did not reach significance. These data do not support the suggestion that asymmetry of strength and power are associated with either increasing age or fall history. Power output showed clear differences between age groups and fall status and appears to be the most relevant measurement of fall risk and highlights the cumulative effects on function of small changes in strength in individual muscle groups.

Prefrontal cortex oxygenation and neuromuscular responses to exhaustive exercise.

Abstract: Near-infrared spectroscopy (NIRS) allows non-invasive monitoring of central and peripheral changes in oxygenation during exercise and may provide valuable insight into the factors affecting fatigue. This study aimed to explore the changes in oxygenation of prefrontal cortex and active muscle tissue as limiting factors of incremental exercise performance in trained cyclists. Thirteen trained healthy subjects (mean +/- SE: age 24.9 +/- 1.5 years, body mass 70.1 +/- 1.2 kg, training 6.1 +/- 0.9 h week(-1)) performed a progressive maximal exercise to exhaustion on a cycling ergometer. Prefrontal cortex (Cox) and vastus lateralis muscle (Mox) oxygenation were measured simultaneously by NIRS throughout the exercise. Maximal voluntary isometric knee torques and quadriceps neuromuscular fatigue (M-wave properties and voluntary activation ratio) were evaluated before and after exercise. Maximal power output and oxygen consumption were 380.8 +/- 7.9 W and 75.0 +/- 2.2 ml min(-1) kg(-1), respectively. Mox decreased significantly throughout exercise while Cox increased in the first minutes of exercise but decreased markedly from the workload corresponding to the second ventilatory threshold up to exhaustion (P < 0.05). No significant difference was noted 6 min after maximal exercise in either the voluntary activation ratio or the M-wave properties. These findings are compatible with the notion that supraspinal modulation of motor output precedes exhaustion.

Physical activity and mental well-being in older people participating in the Better Ageing Project

Abstract: Increasing evidence suggests that physical activity can prevent some aspects of mental illness in older people such as depression, dementia and Alzheimer's disease. Additionally, limited research has shown that engagement in structured exercise can improve aspects of psychological well-being such as mood and self-perceptions in older adults. However, the relationship between incidental daily activity such as walking or time spent sedentary, with psychological well-being has not been investigated. The Better Ageing Project provided an opportunity to assess well-being and quality of life using standardised questionnaires with 176 adults aged 70 and over. Accelerometry was used to objectively assess daily energy expended in physical activity at different levels of intensity. In addition, an assessment of the impact of the 12-month Better Ageing structured group exercise programme was assessed through questionnaires and interviews. Total daily physical activity energy expenditure (joules/day) and amount of time spent in activity of at least moderate intensity were weakly related (r = 0.20-0.28) to quality of life, subjective well-being and physical self-perceptions. Time spent sedentary (min/day) was weakly and negatively related to several mental health indicators. The quantitative data showed only minor psychological benefits of the exercise intervention. In contrast, interviews with 27 research participants and 4 exercise leaders suggested that important improvements in perceived function and social benefits had been experienced.

Resistance training using eccentric overload induces early adaptations in skeletal muscle size

Abstract: Fifteen healthy men performed a 5-week training program comprising four sets of seven unilateral, coupled concentric-eccentric knee extensions 2-3 times weekly. While eight men were assigned to training using a weight stack (WS) machine, seven men trained using a flywheel (FW) device, which inherently provides variable resistance and allows for eccentric overload. The design of these apparatuses ensured similar knee extensor muscle use and range of motion. Before and after training, maximal isometric force (MVC) was measured in tasks non-specific to the training modes. Volume of all individual quadriceps muscles was determined by magnetic resonance imaging. Performance across the 12 exercise sessions was measured using the inherent features of the devices. Whereas MVC increased (P < 0.05) at all angles measured in FW, such a change was less consistent in WS. There was a marked increase (P < 0.05) in task-specific performance (i.e., load lifted) in WS. Average work showed a non-significant 8.7% increase in FW. Quadriceps muscle volume increased (P < 0.025) in both groups after training. Although the more than twofold greater hypertrophy evident in FW (6.2%) was not statistically greater than that shown in WS (3.0%), all four individual quadriceps muscles of FW showed increased (P < 0.025) volume whereas in WS only m. rectus femoris was increased (P < 0.025). Collectively the results of this study suggest more robust muscular adaptations following flywheel than weight stack resistance exercise supporting the idea that eccentric overload offers a potent stimuli essential to optimize the benefits of resistance exercise.

Biomarkers of muscle and cartilage damage and inflammation during a 200 km run

Abstract: Ultra-marathon running is frequently associated with muscle fibre damage However, ultra-marathon related information is scarce The present study evaluated muscle and cartilage biomarkers, and cytokine secretion during a 200 km running event Venous blood samples from 54 trained male ultra-marathon runners (mean ± SD, 457 ± 51 years) Plasma creatine phosphokinase (CPK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate, glucose, high-sensitivity C-reactive protein (Hs-CRP), interleukin-6 (IL-6), TNF-∝ and serum cartilage oligomeric matrix protein (COMP) content were determined before, midway and immediately after the race CPK increased 90-fold (19-fold at 100 km) from pre-race value and LDH increased 37-fold (22-fold at 100 km) AST increased 15-fold (5-fold at 100 km) and ALT increased 39-fold (2-fold at 100 km) Blood lactate and glucose levels did not change significantly Hs-CRP increased 23-fold (3-fold at 100 km) and IL-6 increased 121-fold at 100 km, and then remained stable up to 200 km, whereas TNF-∝ did not change significantly Serum COMP increased 3-fold (13-fold at 100 km) Post-run CPK was correlated with LDH (r = 062, P < 0001), Hs-CRP (r = 045, P < 0001), ALT (r = 089, P < 0001), AST (r = 097, P < 0001), and IL-6 (r = 061, P < 0001) The present study demonstrated that blood biomarkers related to muscle and cartilage damage and inflammation were increased during a 200 km run and that this was particularly marked during the second half of the event Ultra-marathon running clearly has a major impact on muscle and cartilage structures

The effect of rest interval length on metabolic responses to the bench press exercise

Abstract: The purpose of this study was to examine the effects of different rest interval (RI) lengths on metabolic responses to the bench press. Eight resistance-trained men performed 10 randomized protocols [five sets of bench press with 75 or 85% of 1RM for ten (10REP) and five repetitions (5REP), respectively, using different RI (30 s, 1, 2, 3, 5 min)]. Oxygen consumption (VO2) was measured during exercise and for 30 min post exercise. For 30-s and 1-min RI: reductions (15–55%) in resistance and volume were observed (set 5 5REP for all RI except 1-min. Respiratory exchange ratio (RER) was elevated similarly for each protocol. Post exercise, VO2, V E, and RER were elevated through 30 min. No differences between RI were observed following 10REP; however, VO2 after 30-s was higher than 2-, 3-, and 5-min and 1-min was higher than 5-min during 5REP. Fatigue rate was correlated (r = 0.30–0.49) to all metabolic variables. A continuum of performance reductions and metabolic responses were observed. The largest reductions in performance occurred with very short RI (<1 min), and performance was maintained during the first 3–4 sets when 3- and 5-min RI were used.

Effects of differing intensities of static stretching on jump performance.

Abstract: Acute bouts of static stretching have been shown to impair performance. Most published studies have incorporated static stretching that stressed the muscle(s) to the point of discomfort (POD). There are very few studies that have examined the effects of submaximal intensity (less than POD) static stretching on subsequent performance. Ten participants were pre-tested by performing two repetitions of three different stretches to assess range of motion (ROM) and two repetitions each of five different types of jumps. Following pre-testing, participants were stretched four times for 30 s each with 30 s recovery for the quadriceps, hamstrings and plantar flexors at 100% (POD), 75% and 50% of POD or a control condition. Five minutes following the stretch or control conditions, they were tested post-stretch with the same stretches and jumps as the pre-test. All three stretching intensities adversely affected jump heights. With data collapsed over stretching intensities, there were significant decreases in jump height of 4.6% (P=0.01), 5.7% (P<0.0001), 5.4% (P=0.002), 3.8% (P=0.009) and 3.6% (P=0.008) for the drop jump, squat jump, countermovement jump (CMJ) to a knee flexion of 70 degrees , CMJ using a preferred jump strategy and short amplitude CMJ respectively. An acute bout of maximal or submaximal intensity stretching can impair a variety of jumping styles and based on previous research, it is hypothesized that changes in muscle compliance may play a role.

Effect of caffeine ingestion on one-repetition maximum muscular strength.

Abstract: Multiple studies corroborate the ergogenic properties of caffeine (CAF) for endurance performance, yet fewer investigations document the efficacy of acute caffeine intake for intense, short-term exercise. The aim of the study was to determine the ergogenic potential of caffeine during testing of muscular strength and endurance. Twenty-two resistance-trained men ingested CAF (6 mg/kg) or placebo (PL) 1 h pre-exercise in a randomized, double-blind crossover design. They refrained from caffeine intake and strenuous exercise 48 and 24 h, respectively, pre-visit. Initially, resting heart rate and blood pressure were obtained followed by one-repetition maximum (1-RM) testing on the barbell bench press and leg press. Upon determination of 1-RM, participants completed repetitions to failure at 60%1-RM. Heart rate, blood pressure, and rating of perceived exertion (RPE) were measured after the final repetition. Compared to PL, there was no effect (P > 0.05) of caffeine on muscular strength, as 1-RM bench press (116.4 ± 23.6 kg vs. 114.9 ± 22.8 kg) and leg press (410.6 ± 92.4 kg vs. 394.8 ± 95.4 kg) were similar. Total weight lifted during the 60% 1-RM trial was 11 and 12% higher for the bench press and leg press with caffeine compared to placebo, yet did not reach significance. RPE was similar at the end of resistance exercise with CAF vs. PL. Acute caffeine intake does not significantly alter muscular strength or endurance during intense bench press or leg press exercise, yet the practical importance of the increased muscular endurance remains to be explored.

Energy system contributions in indoor rock climbing

Abstract: The present study cross-sectionally investigated the influence of training status, route difficulty and upper body aerobic and anaerobic performance of climbers on the energetics of indoor rock climbing. Six elite climbers (EC) and seven recreational climbers (RC) were submitted to the following laboratory tests: (a) anthropometry, (b) upper body aerobic power, and (c) upper body Wingate test. On another occasion, EC subjects climbed an easy, a moderate, and a difficult route, whereas RC subjects climbed only the easy route. The fractions of the aerobic (W AER), anaerobic alactic (W PCR) and anaerobic lactic $$(W_{{\rm [La}^{-}]})$$ systems were calculated based on oxygen uptake, the fast component of excess post-exercise oxygen uptake, and changes in net blood lactate, respectively. On the easy route, the metabolic cost was significantly lower in EC [40.3 (6.5) kJ] than in RC [60.1 (8.8) kJ] (P < 0.05). The respective contributions of the W AER, W PCR, and $$W_{\rm [La^{-}]}$$ systems in EC were: easy route = 41.5 (8.1), 41.1 (11.4) and 17.4% (5.4), moderate route = 45.8 (8.4), 34.6 (7.1) and 21.9% (6.3), and difficult route = 41.9 (7.4), 35.8 (6.7) and 22.3% (7.2). The contributions of the W AER, W PCR, and $$W_{\rm [La^{-}]}$$ systems in RC subjects climbing an easy route were 39.7 (5.0), 34.0 (5.8), and 26.3% (3.8), respectively. These results indicate that the main energy systems required during indoor rock climbing are the aerobic and anaerobic alactic systems. In addition, climbing economy seems to be more important for the performance of these athletes than improved energy metabolism.

Voluntary activation during maximal contraction with advancing age: a brief review

Abstract: It is well established that the loss of muscle mass (i.e. sarcopenia) is the primary factor contributing to the reduction in muscle force with ageing. Based on the observation that force declines at a faster rate than muscle mass, neural alterations are also thought to contribute to muscle weakness by reducing central drive to the agonist muscles and by increasing coactivation of the antagonist muscles. Researchers have attempted to quantify the contribution of impaired voluntary drive to the decline in muscle force using superimposed electrical stimulation during maximal voluntary contractions (MVCs) and by recording surface electromyographic (EMG) activity. Although reduced voluntary activation of agonist muscles and increased coactivation of antagonist muscles during a MVC have been reported with advancing age, such changes are not supported by all studies. These discrepancies may be explained by differences in sensitivity between the methods used to assess voluntary activation, as well as differences between the characteristics of the study population, the muscle group that is tested, and the type of contraction that is performed. The objective of this review is to summarize current knowledge regarding the activation of agonist and antagonist muscles during MVC in elderly and to try to clarify the disparities in literature concerning the influence of a possible deficit in voluntary activation on the maximal force capacity of muscles in elderly adults.

Exercise as a synchroniser of human circadian rhythms: an update and discussion of the methodological problems.

Abstract: We review the literature on whether exercise is a synchroniser of human circadian rhythms, and highlight the specific methodological problems that are associated with this topic. In applied research, exercise has been investigated as a treatment for jet lag and shift-work problems. In these studies, there have been difficulties in controlling the characteristics of the exercise bout, the athletic status of research participants and exposure to other confounding synchronisers. Therefore, it is unclear at present whether exercise can help mitigate the problems associated with transmeridian travel and shift-work. In laboratory-based experiments, participants have exercised at various times of the day and the change in phase of various circadian rhythms has been measured. Although it is difficult to control for the considerable masking effects of exercise on these estimates of circadian timing, it is clear that nocturnal exercise can induce phase delays in the onset of melatonin. Reports of exercise-induced phase advances of the melatonin rhythm are rarer, as are any phase-shifting effects at all on the body temperature rhythm. In practical terms, the substantial levels of activity needed to obtain phase shifts may not be attainable by the majority of people. In mechanistic terms, the lack of agreement with the phase-shifting effects of bright light suggests that exercise is not exerting its effects via photic entrainment pathways. An alternative explanation may involve exercise-induced hyperthermia. Moreover, it is perplexing why exercise should have a different phase response curve to light, given that humans are diurnally active.

Optimal warm-up stimuli of muscle activation to enhance short and long-term acute jumping performance.

Abstract: The aim of this study was to determine the effect of different types of active warm-up stimuli of muscle activation on explosive jumping performance after short (5 min postwarm-up) and long (6 h postwarm-up) recovery periods following warm-up. Twelve trained volleyball players (21-24 years) performed different types of specific warm-up stimuli (WP) after baseline measurements [e.g., countermovement jump (CMJ) without and with extra load and Drop jump (DJ)] on randomized separate occasions: (1) three sets of five jumps with extra load (WP1), (2) two sets of four reps at 80% of 1RM parallel squat (1RMPS) and two sets of two reps at 85% of 1RMPS (WP2), (3) two sets of four reps at 80% of 1RMPS and two sets of two reps at 90% of 1RMPS and two sets of one rep at 95% of 1RMPS (WP3), (4) three sets of five DJs (WP4), (5) specified warm-up for a volleyball match (WP5), (6) three sets of five reps at 30% 1RMPS (WP6), and (7) an experimental condition of no active warm-up. Height in DJ significantly improved (P < 0.05) after WP1 (4.18%), WP2 (2.98%), WP3 (5.47%), and WP5 (4.49%). Maximal power output during CMJ with extra load significantly improved (P < 0.05) after WP2 (11.39%), WP5 (10.90%), WP3 (9%), and WP1 (2.47%). High-intensity dynamic loading (e.g., 80–95% 1RM), as well as specific volleyball warm-up protocol bring about the greatest effects on subsequent neuromuscular explosive responses. Acute positive effects on jumping performance after warm-up were maintained after long recovery periods (e.g., 6 h following warm-up), particularly when prior high-intensity dynamic actions were performed.

Influence of muscle architecture on the torque and power-velocity characteristics of young and elderly men.

Abstract: This study investigated the contribution of muscle architecture to the differences in the torque-velocity and power-velocity relationships between older (OM n = 9, aged 69-82 years) and younger men (YM n = 15, aged 19-35 years). Plantarflexors' (PF) maximal isometric and concentric torques were recorded at 0.87, 1.75, 2.62, 3.49 and 4.36 rad s(-1). Physiological cross-sectional area (PCSA) was calculated as the ratio of muscle volume (determined by magnetic resonance imaging) to muscle fascicle length (Lf, measured by ultrasonography). GM PCSA and Lf of the OM were, respectively, 14.3% (P < 0.05) and 19.3% (P < 0.05) smaller than of the YM. In the OM, GM maximum isometric torque and maximum contraction velocity (Vmax), estimated from Hill's equation were, respectively, 48.5 and 38.2% lower (P < 0.001) than in the YM. At all contraction velocities, the OM produced less torque than the YM (46.3% of YM at 0.87 rad s(-1) to 14.7% at 4.36 rad s(-1), P < 0.001). Peak power (PP) of the OM was 80% lower than that of the YM and normalisation of PP to muscle volume only reduced this difference by 10%. Normalisation of torque to PCSA reduced, but did not eliminate, differences in torque between YM and OM (9.6%) and differences in torque/PCSA increased with contraction velocity (P < 0.05). After normalisation of velocity to Lf, the difference in Vmax between the OM and the YM was reduced to 15.9%. Thus, although muscle architecture contributes significantly to the differences in the torque- and power-velocity properties of OM and YM, other contractile factors, intrinsic to the muscle, seem to play a role. It is noteworthy that the deficit in PP between OM and YM is far greater than that of muscle torque, even after normalisation of PP to muscle volume. This finding likely plays an important role in the loss of mobility in old age.

Improvement of VO2max by cardiac output and oxygen extraction adaptation during intermittent versus continuous endurance training.

Abstract: Improvement of exercise capacity by continuous (CT) versus interval training (IT) remains debated. We tested the hypothesis that CT and IT might improve peripheral and/or central adaptations, respectively, by randomly assigning 10 healthy subjects to two periods of 24 trainings sessions over 8 weeks in a cross-over design, separated by 12 weeks of detraining. Maximal oxygen uptake (VO2max), cardiac output (Qmax) and maximal arteriovenous oxygen difference (Da-vO2max) were obtained during an exhaustive incremental test before and after each training period. VO2max and Qmax increased only after IT (from 26.3 +/- 1.6 to 35.2 +/- 3.8 ml min(-1) kg(-1) and from 17.5 +/- 1.3 to 19.5 +/- 1.8 l min(-1), respectively; P < 0.01). Da-vO2max increased after both protocols (from 11.0 +/- 0.8 to 12.7 +/- 1.0; P < 0.01 and from 11.0 +/- 0.8 to 12.1 +/- 1.0 ml 100 ml(-1), P < 0.05 in CT and IT, respectively). At submaximal intensity a significant rightward shift of the Q/Da-vO2 relationship appeared only after CT. These results suggest that in isoenergetic training, central and peripheral adaptations in oxygen transport and utilization are training-modality dependant. IT improves both central and peripheral components of Da-vO2max whereas CT is mainly associated with greater oxygen extraction.

Age-related fatigability of the ankle dorsiflexor muscles during concentric and eccentric contractions

Abstract: This study compares the fatigability of the ankle dorsiflexors during five sets of 30 maximal concentric and eccentric contractions in young and elderly adults. The torque produced by the ankle dorsiflexors and the average surface electromyogram (aEMG) of the tibialis anterior were continuously recorded. The contribution of central and peripheral mechanisms to muscle fatigue was tested before, after each set of contractions, and during a 30 min recovery period by the superimposed electrical stimulation method. The compound muscle action potential (M-wave), the mechanical response to single (twitch) and paired (doublet) stimulation, and the postactivation potentiation were also recorded. Compared with young subjects, elderly adults exhibited a greater loss of torque for concentric (50.2 vs. 40.9%; P<0.05) and eccentric (42.1 vs. 27.1%; P < 0.01) contractions. Although young subjects showed a lesser decrease in torque during the eccentric compared with concentric contractions, elderly adults experienced similar fatigability for the two types of contractions despite a comparable depression in the EMG activity of both groups and contraction types (10-20%). As tested by the interpolated-twitch method and aEMG/M-wave ratio, voluntary activation was not altered during either type of contraction or for either age group. During the two fatigue tasks, only elderly adults experienced a decrease in M-wave area (26.4-35.4%; P < 0.05). All together, our results suggest that the fatigue exhibited by both young and elderly adults during maximal concentric and eccentric contractions mainly involved peripheral alterations and that elderly adults may also have experienced a decline in neuromuscular propagation.

The validity of estimating quadriceps volume from single MRI cross-sections in young men.

Abstract: Muscle size is often reported as a single anatomical cross-sectional area (ACSA), rather than volume measured with contiguous MRI scans. However, a single ACSA may provide an inadequate estimate of muscle mass. Therefore, we investigated whether quadriceps muscle volume can be adequately estimated from a single ACSA. In 18 adult males we derived regression equations from which estimates of volume were made. These equations were based on the direct assessment of volume using 11 transverse-plane MRI scans along the entire length of the femur (the gold standard). We estimated volume based on single scans at 40, 50 and 60% of femur length (from the distal end). All estimates of quadriceps volumes were highly correlated to the measured volume and demonstrated a low level of error. R (2) = 0.84, 0.93, 0.90 (all P < 0.01), standard error of estimate (SEE) = 26.8 +/- 5.2, 12.5 +/- 5.4 and 9.9 +/- 5.7%, for single scans taken at 40, 50 and 60% of femur length respectively. In comparison, when volume was estimated using multiple MRI scans corresponding to the maximum ACSA of each muscle the estimate was even better [R (2) = 0.95 (P < 0.01) and SEE = 4.5 +/- 2.7%]. Substituting ACSA from a single MRI scan at 60% of femur length into a previously determined regression equation allows for an estimation of muscle volume with a 10% error of estimate.

Hip, thigh and calf muscle atrophy and bone loss after 5-week bedrest inactivity

Abstract: Unloaded inactivity induces atrophy and functional deconditioning of skeletal muscle, especially in the lower extremities. Information is scarce, however, regarding the effect of unloaded inactivity on muscle size and function about the hip. Regional bone loss has been demonstrated in hips and knees of elderly orthopaedic patients, as quantified by computerized tomography (CT). This method remains to be validated in healthy individuals rendered inactive, including real or simulated weightlessness. In this study, ten healthy males were subjected to 5 weeks of experimental bedrest and five matched individuals served as ambulatory controls. Maximum voluntary isometric hip and knee extension force were measured using the strain gauge technique. Cross-sectional area (CSA) of hip, thigh and calf muscles, and radiological density (RD) of the proximal tibial bone were measured using CT. Bedrest decreased (P 0.05), when examined at similar time intervals. The present findings of a substantial loss in hip extensor strength and a smaller, yet significant atrophy of these muscles, demonstrate that hip muscle deconditioning accompanies losses in thigh and calf muscle mass after bedrest. This suggests that comprehensive quantitative studies on impaired locomotor function after inactivity should include all joints of the lower extremity. Our results also demonstrate that a decreased RD, indicating bone mineral loss, can be shown already after 5 weeks of unloaded bedrest, using a standard CT technique.

Elevated plasma interleukin-6 levels in trained male triathletes following an acute period of intense interval training.

Abstract: The aim of the present study was to investigate possible changes in the plasma IL-6 levels, subjective reporting of sources and symptoms of stress and the innate immune system in response to an acute period of intensified run training in highly trained endurance athletes. Eight healthy endurance trained male subjects (mean +/- SD age 23 +/- 2 years, VO(2max) 64.8 +/- 2.6 ml kg(-1) min(-1), mass 77.1 +/- 2.9 kg) completed the study which took place over a 4 week period. In weeks 2 and 3, in addition to their normal endurance training, subjects completed interval-training run sessions on three successive days. Saliva and venous blood samples were taken at the end of each week. Blood samples were analysed for leukocyte counts; neutrophil function; plasma IL-6; creatine kinase activity; and cortisol. Symptoms and sources of stress were assessed by questionnaire. Plasma IL-6 and creatine kinase activity were elevated following intensified training. Neutrophil function was reduced but total leukocyte and neutrophil counts, plasma cortisol and salivary IgA remained unchanged. There was a worsening in symptoms of stress despite there being no significant change in the sources of stress during intensified training. In conclusion, an acute period of intensified training can induce a suppression of the innate immune system and a chronic elevation in IL-6. This was associated with an increase in fatigue and generalised malaise which lends support to the recent cytokine theories of unexplained, underperformance syndrome.

Physiological characteristics of badminton match play.

Abstract: The present study aimed at examining the physiological characteristics and metabolic demands of badminton single match play. Twelve internationally ranked badminton players (eight women and four men) performed an incremental treadmill test [VO(2peak = )50.3 +/- 4.1 ml min(-1) kg(-1) (women) and 61.8 +/- 5.9 ml min(-1) kg(-1) (men), respectively]. On a separate day, they played a simulated badminton match of two 15 min with simultaneous gas exchange (breath-by-breath) and heart rate measurements. Additionally, blood lactate concentrations were determined before, after 15 min and at the end of the match. Furthermore, the duration of rallies and rests in between, the score as well as the number of shots per rally were recorded. A total of 630 rallies was analysed. Mean rally and rest duration were 5.5 +/- 4.4 s and 11.4 +/- 6.0 s, respectively, with an average 5.1 +/- 3.9 shots played per rally. Mean oxygen uptake (VO(2)), heart rate (HR), and blood lactate concentrations during badminton matches were 39.6 +/- 5.7 ml min(-1) kg(-1) (73.3% VO(2peak)), 169 +/- 9 min(-1) (89.0% HR(peak)) and 1.9 +/- 0.7 mmol l(-1), respectively. For a single subject 95% confidence intervals for VO(2) and HR during match play were on average 45.7-100.9% VO(2peak) and 78.3-99.8% HR(peak). High average intensity of badminton match play and considerable variability of several physiological variables demonstrate the importance of anaerobic alactacid and aerobic energy production in competitive badminton. A well-developed aerobic endurance capacity seems necessary for fast recovery between rallies or intensive training workouts.

Hemodynamic and neurohumoral responses to the restriction of femoral blood flow by KAATSU in healthy subjects

Abstract: The application of an orthostatic stress such as lower body negative pressure (LBNP) has been proposed to minimize the effects of weightlessness on the cardiovascular system and subsequently to reduce the cardiovascular deconditioning. The KAATSU training is a novel method to induce muscle strength and hypertrophy with blood pooling in capacitance vessels by restricting venous return. Here, we studied the hemodynamic, autonomic nervous and hormonal responses to the restriction of femoral blood flow by KAATSU in healthy male subjects, using the ultrasonography and impedance cardiography. The pressurization on both thighs induced pooling of blood into the legs with pressure-dependent reduction of femoral arterial blood flow. The application of 200 mmHg KAATSU significantly decreased left ventricular diastolic dimension (LVDd), cardiac output (CO) and diameter of inferior vena cava (IVC). Similarly, 200 mmHg KAATSU also decreased stroke volume (SV), which was almost equal to the value in standing. Heart rate (HR) and total peripheral resistance (TPR) increased in a similar manner to standing with slight change of mean blood pressure (mBP). High-frequency power (HFRR) decreased during both 200 mmHg KAATSU and standing, while low-frequency/high-frequency power (LFRR/HFRR) increased significantly. During KAATSU and standing, the concentration of noradrenaline (NA) and vasopressin (ADH) and plasma renin activity (PRA) increased. These results indicate that KAATSU in supine subjects reproduces the effects of standing on HR, SV, TPR, etc., thus stimulating an orthostatic stimulus. And, KAATSU training appears to be a useful method for potential countermeasure like LBNP against orthostatic intolerance after spaceflight.

Closing volume: a reappraisal (1967-2007).

Abstract: Measurement of closing volume (CV) allows detection of presence or absence of tidal airway closure, i.e. cyclic opening and closure of peripheral airways with concurrent (1) inhomogeneity of distribution of ventilation and impaired gas exchange; and (2) risk of peripheral airway injury. Tidal airway closure, which can occur when the CV exceeds the end-expiratory lung volume (EELV), is commonly observed in diseases characterised by increased CV (e.g. chronic obstructive pulmonary disease, asthma) and/or decreased EELV (e.g. obesity, chronic heart failure). Risk of tidal airway closure is enhanced by ageing. In patients with tidal airway closure (CV > EELV) there is not only impairment of pulmonary gas exchange, but also peripheral airway disease due to injury of the peripheral airways. In view of this, the causes and consequences of tidal airway closure are reviewed, and further studies are suggested. In addition, assessment of the "open volume", as opposed to the "closing volume", is proposed because it is easier to perform and it requires less equipment.

Steadiness of quadriceps contractions in young and older adults with and without a history of falling.

Abstract: Decreased steadiness of muscle force may be associated with ageing and could be a cause of falls in older people. We studied this in isometric and anisometric quadriceps contractions in healthy young and older people. The older group contained people with and without a history of medically unexplained falls. Forty-four young (aged 18–40 years) and 78 older (aged > 70 years) subjects participated. In the latter group 34 people had a history of falling (fallers) and 44 did not (non-fallers). Isometric steadiness was measured by the coefficient of variation (CoV) of force at 10, 25 and 50% maximal voluntary force (MVC). Anisometric steadiness was measured by the SD of acceleration during concentric and eccentric contractions against two external loads (1 and 5 kg). There was an overall trend for the younger subjects to be most steady and the fallers the least but the differences were not consistently significant. Isometric steadiness was unaffected by force in all groups. The fallers were less steady (P < 0.001) than both the young and non-fallers, who had similar values. During anisometric contractions, steadiness was similar with both external loads and types of contraction in all groups. During dynamic contractions the older subjects were less steady (P < 0.002). Only eccentric contractions distinguished between the two older groups, with the fallers being less steady by 31% (P = 0.013). These data indicate ageing per se is associated with decreased anisometric, but not isometric, steadiness. Greater unsteadiness during eccentric contractions in the fallers could be an important mechanism of medically unexplained falls.