Changes in muscle metabolites in females with 30-s exhaustive exercise

Upper limb cranking asymmetry during a Wingate anaerobic test in wheelchair basketball players

INTRODUCTION

Interlimb asymmetry of strength and/or motor coordination could limit the performance of wheelchair athletes or increase their risk of injury. Studies of interlimb asymmetry in the lower limbs have shown high between-subject variability that does not depend on the side of dominance and that does not change with fatigue. Upper limb asymmetry is particularly large in manual wheelchair athletes with a lower degree of impairment. The aim of this study was to evaluate interlimb asymmetry of forces developed during an upper limb Wingate anaerobic test, the effects of fatigue on force, and differences between high- and low-point players.

METHOD

Twenty-five wheelchair basketball players (13 females and 12 males) of male and female national French teams performed a 30s anaerobic Wingate test on an arm ergometer. Participants were classified into two functional categories, high-point (classed from 3 to 4.5) and low-point (classed from 1 to 2.5), according to the International Wheelchair Basketball Federation classification. Left and right arm forces were measured during the pushing and pulling phases at peak power, 10s, and the end of the 30s test.

RESULTS

Upper limb asymmetry changed with fatigue during each phase. Force asymmetry differed between peak power, 10s and 30s, with no consistent increase or decrease. Asymmetry did not differ significantly between low- and high-point players but tended to be greater in high-point players. Asymmetry tended to be greater in the females, with significant differences between the males and females in the push phase.

CONCLUSION

Inter-subject variability was high, but forces were asymmetric for most participants, especially females. The Wingate anaerobic test could highlight problematic asymmetries that might impact daily life or sports performance.

Effect of Exercise Training on Fat Loss-Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution

In obesity, excessive abdominal fat, especially the accumulation of visceral adipose tissue (VAT), increases the risk of metabolic disorders, such as type 2 diabetes mellitus (T2DM), cardiovascular disease, and non-alcoholic fatty liver disease. Excessive abdominal fat is associated with adipose tissue dysfunction, leading to systemic low-grade inflammation, fat overflow, ectopic lipid deposition, and reduced insulin sensitivity. Physical activity is recommended for primary prevention and treatment of obesity, T2DM, and related disorders. Achieving a stable reduction in body weight with exercise training alone has not shown promising effects on a population level. Because fat has a high energy content, a large amount of exercise training is required to achieve weight loss. However, even when there is no weight loss, exercise training is an effective method of improving body composition (increased muscle mass and reduced fat) as well as increasing insulin sensitivity and cardiorespiratory fitness. Compared with traditional low-to-moderate-intensity continuous endurance training, high-intensity interval training (HIIT) and sprint interval training (SIT) are more time-efficient as exercise regimens and produce comparable results in reducing total fat mass, as well as improving cardiorespiratory fitness and insulin sensitivity. During high-intensity exercise, carbohydrates are the main source of energy, whereas, with low-intensity exercise, fat becomes the predominant energy source. These observations imply that HIIT and SIT can reduce fat mass during bouts of exercise despite being associated with lower levels of fat oxidation. In this review, we explore the effects of different types of exercise training on energy expenditure and substrate oxidation during physical activity, and discuss the potential effects of exercise training on adipose tissue function and body fat distribution.

Comparison between the 10- and the 30-s-long Wingate Anaerobic Test in summer Paralympic athletes with a lower limb impairment

Background

The 30-s-long Wingate Anaerobic Test (WAnT_30s) has some limitations in high-level athletes. A shorter version might be helpful for both clinical applications and performance assessment. The comparison between the traditional WAnT_30s and a shorter version has never been carried out yet in Paralympic athletes.

Aim

To assess if a 10-s-long Wingate Anaerobic Test (WAnT_10s) could be used to accurately assess and predict the anaerobic components of physical fitness as an alternative to the traditional WAnT_30s in male Paralympic athletes.

Methods

Forty-four trained male Paralympic Athletes grouped by severity of locomotor impairment completed the WAnT_30s and the WAnT_10s with an arm cranking ergometer. Differences between mean and peak power achieved throughout both WAnTs were analysed using a mixed-design analysis of variance and predictivity was assessed by stepwise linear regression analysis.

Results

In the whole sample, peak power values were similar (P > 0.005) in the two tests and the WAnT_10s mean power was significantly higher than that in the WAnT_30s (P < 0.005). Finally, the mean power measured during WAnT_30s showed high level of predictability from mean power measured during WAnT_10s and the Functional class (adjusted R2 = 0.906; P < 0.001).

Conclusion

The WAnT_10s is accurate to assess peak power, is definitively appropriate to evaluate the alactic anaerobic metabolism and seems able to predict the mean power as traditionally evaluated through a WAnT_30s in male Paralympic Athletes. Thus, it can be used to assess the anaerobic components of physical fitness in this athletic population.

p38 MAPK activation and H3K4 trimethylation is decreased by lactate in vitro and high intensity resistance training in human skeletal muscle

Exercise induces adaptation of skeletal muscle by acutely modulating intracellular signaling, gene expression, protein turnover and myogenic activation of skeletal muscle stem cells (Satellite cells, SCs). Lactate (La)-induced metabolic stimulation alone has been shown to modify SC proliferation and differentiation. Although the mechanistic basis remains elusive, it was demonstrated that La affects signaling via p38 mitogen activated protein kinase (p38 MAPK) which might contribute to trimethylation of histone 3 lysine 4 (H3K4me3) known to regulate satellite cell proliferation and differentiation. We investigated the effects of La on p38 MAPK and H3K4me3 in a model of activated SCs. Differentiating C2C12 myoblasts were treated with La (20 mM) and samples analysed using qRT-PCR, immunofluorescence, and western blotting. We determined a reduction of p38 MAPK phosphorylation, decreased H3K4me3 and reduced expression of Myf5, myogenin, and myosin heavy chain (MHC) leading to decreased differentiation of La-treated C2C12 cells after 5 days of repeated La treatment. We further investigated whether this regulatory pathway would be affected in human skeletal muscle by the application of two different resistance exercise regimes (RE) associated with distinct metabolic demands and blood La accumulation. Muscle biopsies were obtained 15, 30 min, 1, 4, and 24 h post exercise after moderate intensity RE (STD) vs. high intensity RE (HIT). Consistent with in vitro results, reduced p38 phosphorylation and blunted H3K4me3 were also observed upon metabolically demanding HIT RE in human skeletal muscle. Our data provide evidence that La-accumulation acutely affects p38 MAPK signaling, gene expression and thereby cell differentiation and adaptation in vitro, and likely in vivo.

Changes in the acid-base balance and lactate concentration in the blood in amateur ultramarathon runners during a 100-km run

The aim of this study was to analyse the acid-base balance and partial pressure of blood gases of participants during a 100-km run. Fourteen experienced amateur ultramarathon runners (age: 43.36±11.83 years; height: 175.29±6.98 cm; weight: 72.12±7.36 kg) completed the 100-km run. Blood samples were taken before the run; after 25, 50, 75, and 100 km; and 12 and 24 hours after the run. There were significant differences (p<0.05) between the mean values registered for acid-alkaline balance, buffering alkalies, and current bicarbonate in each segment of the run, especially during the third, fourth, and fifth segments of the run (i.e., between 50 and 100 km), and there were only significant differences associated with buffering alkalies and current bicarbonate during the recovery. However, all the changes were within the physiological norm. A significant decrease in the compressibility of oxygen was observed after 100 km (from 92.80±15.67 to 88.36±13.71 mmHg) and continued during the recovery to 75.06±8.60 mmHg 12 h after the run. Also there was a decrease in saturation to a mean value of 93.78±3.10 at 12 h after the run. Generally the amateurs runners are able to adjust their running speed so as not to provoke a significant acid-base imbalance or lactate acid accumulation.

Reliability and validity of a 20-s alternative to the wingate anaerobic test in team sport male athletes

The intent of this study was to evaluate relative and absolute reliability of the 20-s anaerobic test (WAnT20) versus the WAnT30 and to verify how far the various indices of the 30-s Wingate anaerobic test (WAnT30) could be predicted from the WAnT20 data in male athletes. The participants were Exercise Science majors (age: 21.5±1.6 yrs, stature: 0.183±0.08 m, body mass: 81.2±10.9 kg) who participated regularly in team sports. In Phase I, 41 participants performed duplicate WAnT20 and WAnT30 tests to assess reliability. In Phase II, 31 participants performed one trial each of the WAnT20 and WAnT30 to determine the ability of the WAnT20 to predict components of the WAnT30. In Phase III, 31 participants were used to cross-validate the prediction equations developed in Phase II. Respective intra-class correlation coefficients (ICC) for peak power output (PPO) (ICC = 0.98 and 0.95) and mean power output (MPO) (ICC 0.98 and 0.90) did not differ significantly between WAnT20 and WAnT30. ICCs for minimal power output (POmin) and fatigue index (FI) were poor for both tests (range 0.53 to 0.76). Standard errors of the means (SEM) for PPO and MPO were less than their smallest worthwhile changes (SWC) in both tests; however, POmin and FI values were "marginal," with SEM values greater than their respective SWCs for both tests values. Stepwise regression analysis showed that MPO had the highest coefficient of predictability (R = 0.97), with POmin and FI considerable lower (R = 0.71 and 0.41 respectively). Cross-validation showed insignificant bias with limits of agreement of 0.99±1.04, 6.5±92.7 W, and 1.6±9.8% between measured and predicted MPO, POmin, and FI, respectively. WAnT20 offers a reliable and valid test of leg anaerobic power in male athletes and could replace the classic WAnT30.

Fatigue index and fatigue rate during an anaerobic performance under hypohydrations

Background

Since hypohydration commonly occurs in sports, studies on anaerobic exercise performance under this condition have been extensively carried out. When describing anaerobic performance, authors usually refer to a drop in anaerobic performance as fatigue index (FI) which is conventionally calculated using peak and low power data points. Meanwhile, another possible method in explaining anaerobic fatigue is using the rate constant which is derived from the exponential decline of power output known as fatigue rate (FR). Few studies have demonstrated that there was no change in anaerobic performance under mild hypohydrations.

Purpose

This study aimed to compare the kinetics of power output using FI and FR of an anaerobic performance (Wingate test) under 2, 3 and 4% state of hypohydrations.

Method

Thirty two collegiate cyclists (age  = 22±2 years; body weight  = 71.45±3.43 kg; height  = 173.23±0.04 cm) were matched using their baseline anaerobic peak power (APP) then randomly divided into 4 groups of EU (euhydrated), 2H, 3H and 4H respectively.

Results

As expected the, FI, APP, anaerobic lower power (ALP) and rating of perceived exertion (RPE) did not show significant differences between and within the groups. However, the FR in 3H (0.018±0.005s⁻¹) and 4H (0.019±0.010s⁻¹) were significantly lower than EU (0.033±0.012s⁻¹). Post-test FR also showed significant reduction in 3H and 4H compared to their pre-test values (p<0.05).

Conclusion

Despite the lack of changes in APP and RPE, subjects in 3H and 4H showed evidence of lower reduction of power output over time. The findings support earlier reports which showed no change in anaerobic performance under mild hypohydrations. The relatively lower FR suggests higher drive in maintaining power output under hypohydrations of 3 and 4% body weight.

The role of skeletal muscle glycogen breakdown for regulation of insulin sensitivity by exercise

Glycogen is the storage form of carbohydrates in mammals. In humans the majority of glycogen is stored in skeletal muscles (∼500 g) and the liver (∼100 g). Food is supplied in larger meals, but the blood glucose concentration has to be kept within narrow limits to survive and stay healthy. Therefore, the body has to cope with periods of excess carbohydrates and periods without supplementation. Healthy persons remove blood glucose rapidly when glucose is in excess, but insulin-stimulated glucose disposal is reduced in insulin resistant and type 2 diabetic subjects. During a hyperinsulinemic euglycemic clamp, 70-90% of glucose disposal will be stored as muscle glycogen in healthy subjects. The glycogen stores in skeletal muscles are limited because an efficient feedback-mediated inhibition of glycogen synthase prevents accumulation. De novo lipid synthesis can contribute to glucose disposal when glycogen stores are filled. Exercise physiologists normally consider glycogen's main function as energy substrate. Glycogen is the main energy substrate during exercise intensity above 70% of maximal oxygen uptake ([Formula: see text]) and fatigue develops when the glycogen stores are depleted in the active muscles. After exercise, the rate of glycogen synthesis is increased to replete glycogen stores, and blood glucose is the substrate. Indeed insulin-stimulated glucose uptake and glycogen synthesis is elevated after exercise, which, from an evolutional point of view, will favor glycogen repletion and preparation for new "fight or flight" events. In the modern society, the reduced glycogen stores in skeletal muscles after exercise allows carbohydrates to be stored as muscle glycogen and prevents that glucose is channeled to de novo lipid synthesis, which over time will causes ectopic fat accumulation and insulin resistance. The reduction of skeletal muscle glycogen after exercise allows a healthy storage of carbohydrates after meals and prevents development of type 2 diabetes.

Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise

High-intensity exercise can result in up to a 1,000-fold increase in the rate of ATP demand compared to that at rest (Newsholme et al., 1983). To sustain muscle contraction, ATP needs to be regenerated at a rate complementary to ATP demand. Three energy systems function to replenish ATP in muscle: (1) Phosphagen, (2) Glycolytic, and (3) Mitochondrial Respiration. The three systems differ in the substrates used, products, maximal rate of ATP regeneration, capacity of ATP regeneration, and their associated contributions to fatigue. In this exercise context, fatigue is best defined as a decreasing force production during muscle contraction despite constant or increasing effort. The replenishment of ATP during intense exercise is the result of a coordinated metabolic response in which all energy systems contribute to different degrees based on an interaction between the intensity and duration of the exercise, and consequently the proportional contribution of the different skeletal muscle motor units. Such relative contributions also determine to a large extent the involvement of specific metabolic and central nervous system events that contribute to fatigue. The purpose of this paper is to provide a contemporary explanation of the muscle metabolic response to different exercise intensities and durations, with emphasis given to recent improvements in understanding and research methodology.

Influence of custom-made mouth guards on strength, speed and anaerobic performance of taekwondo athletes

The purpose of this study was to test the influence of custom-made mouth guards on strength and anaerobic performance of taekwondo athletes. The study included 21 (11 male and 10 female) trained subjects participating in taekwondo. Anaerobic power and anaerobic capacity, isokinetic quadriceps and hamstring strength, handgrip strength, isometric lower extremity and back strength, 20 m sprint time, squat and counter movement jumping height were measured in two randomized conditions: with or without custom-made (CM) mouth guards. No significant differences were observed between the two conditions (with or without CM mouth guards) in 20 m sprint time, jumping tests, handgrip strength, isometric leg or back strength. On the other hand, peak power and average power in Wingate Anaerobic Test and Hamstring Isokinetic Peak Torque significantly increased as a result of wearing mouth guard (P < 0.05). In conclusion, we can suggest that taekwondo athletes can use CM mouth guards without any negative effects on their strength and anaerobic performance.

Anaerobic performance in masters athletes

With increasing age, it appears that masters athletes competing in anaerobic events (10–100 s) decline linearly in performance until 70 years of age, after which the rate of decline appears to accelerate. This decline in performance appears strongly related to a decreased anaerobic work capacity, which has been observed in both sedentary and well-trained older individuals. Previously, a number of factors have been suggested to influence anaerobic work capacity including gender, muscle mass, muscle fiber type, muscle fiber size, muscle architecture and strength, substrate availability, efficiency of metabolic pathways, accumulation of reaction products, aerobic energy contribution, heredity, and physical training. The effects of sedentary aging on these factors have been widely discussed within literature. Less data are available on the changes in these factors in masters athletes who have continued to train at high intensities with the aim of participating in competition. The available research has reported that these masters athletes still demonstrate age-related changes in these factors. Specifically, it appears that morphological (decreased muscle mass, type II muscle fiber atrophy), muscle contractile property (decreased rate of force development), and biochemical changes (changes in enzyme activity, decreased lactate production) may explain the decreased anaerobic performance in masters athletes. However, the reduction in anaerobic work capacity and subsequent performance may largely be the result of physiological changes that are an inevitable result of the aging process, although their effects may be minimized by continuing specific high-intensity resistance or sprint training.

Cross-validation of the 20- versus 30-s Wingate anaerobic test

The 30-s Wingate anaerobic test (30-WAT) is the most widely accepted protocol for measuring anaerobic response, despite documented physical side effects. Abbreviation of the 30-WAT without loss of data could enhance subject compliance while maintaining test applicability. The intent of this study was to quantify the validity of the 20-s Wingate anaerobic test (20-WAT) versus the traditional 30-WAT. Fifty males (mean +/- SEM; age = 20.5 +/- 0.3 years; Ht = 1.6 +/- 0.01 m; Wt = 75.5 +/- 2.6 kg) were randomly selected to either a validation (N = 35) or cross-validation group (N = 15) and completed a 20-WAT and 30-WAT in double blind, random order on separate days to determine peak power (PP; W kg(-1)), mean power (MP; W kg(-1)), and fatigue index (FI; %). Utilizing power outputs (relative to body mass) recorded during each second of both protocols, a non-linear regression equation (Y (20WAT+10 )= 31.4697 e(-0.5)[ln(X (second)/1174.3961)/2.6369(2)]; r (2) = 0.97; SEE = 0.56 W kg(-1)) successfully predicted (error approximately 10%) the final 10 s of power outputs in the cross-validation population. There were no significant differences between MP and FI between the 20-WAT that included the predicted 10 s of power outputs (20-WAT+10) and the 30-WAT. When derived data were subjected to Bland-Altman analyses, the majority of plots (93%) fell within the limits of agreement (+/-2SD). Therefore, when compared to the 30-WAT, the 20-WAT may be considered a valid alternative when used with the predictive non-linear regression equation to derive the final power output values.

Effects of low and high levels of moderate hypoxia on anaerobic energy release during supramaximal cycle exercise

The purpose of this study was to investigate whether hypoxia can alter anaerobic energy release during supramaximal exercise. Seven male subjects performed 12 submaximal cycling tests to establish the relationship between workload and O2 demand. The subjects also performed 40 s Wingate tests (WT) under normoxia (room air), two levels of moderate hypoxia of 16.4% O2 and 12.7% O2. We measured the power output and oxygen uptake (VO2) during each test and estimated the O2 demand, O2 deficit and percentage of anaerobic energy release (%AnAER). These data were analyzed for each 20 s interval. At all intervals, there were no differences in Pmean per body mass (BM)(-1), O2 demand per BM(-1) or O2 deficit per BM(-1) among the three O2 conditions. However, under hypoxia of 12.7%, VO2 per BM(-1) was significantly decreased and %AnAER was significantly increased in the late phase (20-40 s) of the WT, compared to normoxia (P<0.05). There were no such significant differences between normoxia and hypoxia of 16.4%. Thus, the present results show that the degree of hypoxia affects the magnitude of the hypoxia-induced increase in anaerobic energy release in the late phase of the WT and suggest that certain degrees of hypoxia induce significant increases in the amount of anaerobic energy released, compared to normoxia.

Effect of ribose supplementation on resynthesis of adenine nucleotides after intense intermittent training in humans

The effect of oral ribose supplementation on the resynthesis of adenine nucleotides and performance after 1 wk of intense intermittent exercise was examined. Eight subjects performed a random double-blind crossover design. The subjects performed cycle training consisting of 15 x 10 s of all-out sprinting twice per day for 7 days. After training the subjects received either ribose (200 mg/kg body wt; Rib) or placebo (Pla) three times per day for 3 days. An exercise test was performed at 72 h after the last training session. Immediately after the last training session, muscle ATP was lowered (P < 0.05) by 25 +/- 2 and 22 +/- 3% in Pla and Rib, respectively. In both Pla and Rib, muscle ATP levels at 5 and 24 h after the exercise were still lower (P < 0.05) than pretraining. After 72 h, muscle ATP was similar (P > 0.05) to pretraining in Rib (24.6 +/- 0.6 vs. 26.2 +/- 0.2 mmol/kg dry wt) but still lower (P < 0.05) in Pla (21.1 +/- 0.5 vs. 26.0 +/- 0.2 mmol/kg dry wt) and higher (P < 0.05) in Rib than in Pla. Plasma hypoxanthine levels after the test performed at 72 h were higher (P < 0.05) in Rib compared with Pla. Mean and peak power outputs during the test performed at 72 h were similar (P > 0.05) in Pla and Rib. The results support the hypothesis that the availability of ribose in the muscle is a limiting factor for the rate of resynthesis of ATP. Furthermore, the reduction in muscle ATP observed after intense training does not appear to be limiting for high-intensity exercise performance.

Musculoskeletal Response to Exercise Is Greatest in Women with Low Initial Values

INTRODUCTION

The "initial values" principle of exercise training states those with the lowest initial values of a physiologic system have the greatest capacity for improvement in response to training. We sought to determine whether initial values predicted the musculoskeletal response to training in premenopausal women (N = 31) who participated in a 1-yr program of resistance and jump training designed to improve physical indices of fracture risk. Significant improvements in trochanteric bone mineral density (BMD), hip abductor strength, power, and postural stability occurred in response to training.

METHODS

To determine the predictive power of initial values, we performed separate stepwise regression analyses for each variable including the following dependent variables: age, initial value, highest weight lifted during training, and total number of exercise sessions attended.

RESULTS

In each case, the initial value was the most significant predictor of percent change in response to training. Initial values explained 15-29% of the variance in the magnitude of the training response. For each unit lower BMD of the greater trochanter (0.01 g.cm-2), the training response was 12% greater. For each unit decrease in initial strength (1 N.m), power (1 W), and stability (1 SI unit), the training response was 1.0%, 0.2%, and 8.0% greater, respectively. When categorized by quartile of initial values, women in the lowest quartile had two- to fivefold greater improvements in musculoskeletal measures than those in the upper quartile.

CONCLUSION

Women who began training with the lowest initial values had the greatest improvements in hip BMD, hip abductor strength, leg power, and postural stability. These results support the training principle of initial values and suggest that this training program may be most successful in premenopausal women with lower values of musculoskeletal indices of fracture risk.

Energy system interaction and relative contribution during maximal exercise

There are 3 distinct yet closely integrated processes that operate together to satisfy the energy requirements of muscle. The anaerobic energy system is divided into alactic and lactic components, referring to the processes involved in the splitting of the stored phosphagens, ATP and phosphocreatine (PCr), and the nonaerobic breakdown of carbohydrate to lactic acid through glycolysis. The aerobic energy system refers to the combustion of carbohydrates and fats in the presence of oxygen. The anaerobic pathways are capable of regenerating ATP at high rates yet are limited by the amount of energy that can be released in a single bout of intense exercise. In contrast, the aerobic system has an enormous capacity yet is somewhat hampered in its ability to delivery energy quickly. The focus of this review is on the interaction and relative contribution of the energy systems during single bouts of maximal exercise. A particular emphasis has been placed on the role of the aerobic energy system during high intensity exercise. Attempts to depict the interaction and relative contribution of the energy systems during maximal exercise first appeared in the 1960s and 1970s. While insightful at the time, these representations were based on calculations of anaerobic energy release that now appear questionable. Given repeated reproduction over the years, these early attempts have lead to 2 common misconceptions in the exercise science and coaching professions. First, that the energy systems respond to the demands of intense exercise in an almost sequential manner, and secondly, that the aerobic system responds slowly to these energy demands, thereby playing little role in determining performance over short durations. More recent research suggests that energy is derived from each of the energy-producing pathways during almost all exercise activities. The duration of maximal exercise at which equal contributions are derived from the anaerobic and aerobic energy systems appears to occur between 1 to 2 minutes and most probably around 75 seconds, a time that is considerably earlier than has traditionally been suggested.

Aerobic and anaerobic power responses to the practice of taekwon-do

BACKGROUND

Practising the martial art of taekwon-do (TKD) has been proposed to have beneficial effects on cardiovascular fitness as well as general physical ability. Furthermore, TKD masters and participants have promoted TKD as a total fitness programme. Research studies substantiating this, however, seem to be lacking, perhaps because TKD is recognised more as a method of self defence than a fitness programme.

METHODS

Nineteen TKD practitioners with an average age of 13.8 years and 10.4 months of TKD training experience were recruited to participate. Measurements included resting heart rate, aerobic power, anaerobic power, and anaerobic capacity.

RESULTS

Paired t test analysis showed no significant differences in either resting heart rate or aerobic power after training. However, significant differences were observed in anaerobic power and anaerobic capacity (p = 0.05). The increases in anaerobic power and anaerobic capacity were 28% and 61.5% respectively.

CONCLUSION

The practice of TKD promotes anaerobic power and anaerobic capacity, but not aerobic power, in male adolescents.

Detraining reverses positive effects of exercise on the musculoskeletal system in premenopausal women

We studied the effects of a 6-month withdrawal of exercise after 12 months of progressive impact (jump) plus lower body resistance training on risk factors for hip fracture in premenopausal women (age, 30-45 years). Twenty-nine women completed the 12-month training and detraining programs and were compared with 22 matched controls. Bone mineral density (BMD) at the greater trochanter, femoral neck, lumbar spine, and whole body and body composition (% body fat) were measured by dual energy X-ray absorptiometry (DXA; Hologic QDR-1000/W). Knee extensor and hip abductor strength were assessed via isokinetic dynamometry (Kin-Com 500H); maximum leg power was tested using a Wingate Anaerobic Power test; and dynamic postural stability was measured on a stabilimeter (Biodex). All measurements were conducted at baseline, 12 months and 18 months with an additional midtraining measurement of BMD. Exercisers trained three times per week in a program of 100 jumps and 100 repetitions of resistance exercises at each session. Intensity was increased using weighted vests to final values of 10% and 13% of body weight (BW) for jump and resistance exercises, respectively. Differences between groups from training were analyzed by repeated measures analysis of covariance (ANCOVA), adjusted for baseline values. Detraining effects were analyzed by comparing the changes from training with the changes from detraining using repeated measures analysis of variance (ANOVA). Baseline values were not significantly different between exercisers and controls. Percent change over the training period was significantly greater in the exercise group than in the control group at the greater trochanter (2.7 +/- 2.5% vs. 0.8 +/- 0.8%, respectively; p < 0.01) and approached significance at the femoral neck (1.2 +/- 3.2% vs. -0.3 +/- 1.9%, respectively; p = 0.06). Significant improvements also were observed in exercisers versus controls for strength and power with exercisers increasing 13-15% above controls, whereas stability was not different between groups. After 6 months of detraining, BMD and muscle strength and power decreased significantly toward baseline values, whereas control values did not change. We conclude that the positive benefits of impact plus resistance training on the musculoskeletal system in premenopausal women reverse when training is withdrawn. Therefore, continued training, perhaps at a reduced frequency and intensity, is required to maintain the musculoskeletal benefit from exercise that may lower fracture risk in later life.

Body composition predicts bone mineral density and balance in premenopausal women

Low bone mineral density (BMD) and poor stability both contribute to increased risk of fractures associated with a fall. Our aim in this cross-sectional study was to determine the anthropometric and/or performance variables that best predicted BMD and stability in women. BMD, body composition, muscle strength, muscle power, and dynamic stability were evaluated in 61 women (age 40 +/- 4 years; % body fat 27% +/- 5%). In correlation analyses, BMD at all sites was significantly related to height, lean mass, strength, and leg power (r2 = 0.25-0.49). Significant inverse relationships were found between all independent variables and dynamic stability (r2 = 0.23-0.52). In stepwise regression, lean mass independently predicted BMD at the femoral neck (R2 = 0.20), total hip (R2 = 0.24), and whole body (R2 = 0.17), whereas hip abductor torque predicted 23% of the variance in trochanter BMD and added 6% to the variance in total hip BMD. Leg power was the only predictor of spine BMD (R2 = 0.14). Fat and lean mass both independently predicted poor performance on postural stability, with fat mass contributing 31% of the total variance (R2 = 0.38). In conclusion, we found lean mass to be a robust predictor of BMD in premenopausal women. Furthermore, both hip abductor torque and leg power independently predicted BMD at clinically relevant fracture sites (hip and spine). The finding that higher fat mass contributes to the majority of the variance in poor stability indicates that greater fat mass may compromise stability and, thus, increase fall risk in heavier individuals.

Variable resistance all-out test to generate accumulated oxygen deficit and predict anaerobic capacity

A supramaximal variable resistance test over varying time intervals was evaluated as an instrument for the assessment of a number of anaerobic parameters, including the accumulated oxygen deficit (AOD). Eight active men [age, 22 +/- 1 (SEM 1) years, peak oxygen uptake, 53.1 (SEM 2.1) ml x kg-1 x min-1] completed three randomly ordered all-out sprints of 45-, 60- and 90-s duration. Two incremental pretests consisting of three 5-min stages at power outputs of 45, 135, 225 W and 90, 180, 270 W were performed to establish individual efficiency relationships [r = 0.996 (SEE 1.1) ml x kg-1 x min-1]. These relationships were used to estimate energy demand (millilitres per kilogram of oxygen equivalents in 15-s time intervals) during the supramaximal tests. The AOD for the 45 [47.6 (SEM 1.5) ml x kg-1], 60 [49.0 (SEM 1.8) ml x kg-1] and 90 s [49.6 (SEM 1.7) ml x kg-1] tests were significantly different only for the 45 and 90-s tests. Evaluation of the 90-s test indicated that maximal or near-maximal (98%) anaerobic energy release was achieved in 60 s, with the AOD beginning to plateau after this time. No significant differences among tests were found for peak power, time to peak power and peak pedalling rate. Differences in mean power, total work and relative power decrement were related to the length of the test.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolic responses of human type I and II muscle fibres during maximal treadmill sprinting

1. Muscle biopsy samples were obtained from the vastus lateralis of six healthy volunteers before and after 30 s of treadmill sprinting. A portion of each biopsy sample was used for mixed-fibre metabolite analysis. Single fibres were dissected from the remaining portion of each biopsy and were used for ATP, phosphocreatine (PCr) and glycogen determination. 2. Before exercise, PCr and glycogen contents were higher in type II fibres (79.3 +/- 2.7 and 472 +/- 35 mmol (kg dry matter (DM)-1, respectively) compared with type I fibres (71.3 +/- 3.0 mmol (kg DM)-1, P < 0.01 and 375 +/- 25 mmol (kg DM)-1, P < 0.001, respectively). 3. Peak power output was 885 +/- 66 W and declined by 65 +/- 3% during exercise. Phosphocreatine and glycogen degradation in type II fibres during exercise (74.3 +/- 2.5 and 126.3 +/- 15.8 mmol (kg DM)-1, respectively) was greater than the corresponding degradation in type I fibres (59.1 +/- 2.9 mmol (kg DM)-1, P < 0.001 and 77.0 +/- 14.3 mmol (kg DM)-1, P < 0.01, respectively). The decline in ATP during exercise was similar when comparing fibre types (P > 0.05). 4. Compared with previous studies involving similar durations of maximal cycling exercise, isokinetic knee extension and intermittent isometric contraction, the rates of substrate utilization recorded in type I fibres were extremely high, being close to the rapid rates observed in this fibre type during intense contraction with limb blood flow occluded.

Acute and chronic response of skeletal muscle to resistance exercise

Skeletal muscle tissue is sensitive to the acute and chronic stresses associated with resistance training. These responses are influenced by the structure of resistance activity (i.e. frequency, load and recovery) as well as the training history of the individuals involved. There are histochemical and biochemical data which suggest that resistance training alters the expression of myosin heavy chains (MHCs). Specifically, chronic exposure to bodybuilding and power lifting type activity produces shifts towards the MHC I and IIb isoforms, respectively. However, it is not yet clear which training parameters trigger these differential expressions of MHC isoforms. Interestingly, many programmes undertaken by athletes appear to cause a shift towards the MHC I isoform. Increments in the cross-sectional area of muscle after resistance training can be primarily attributed to fibre hypertrophy. However, there may be an upper limit to this hypertrophy. Furthermore, significant fibre hypertrophy appears to follow the sequence of fast twitch fibre hypertrophy preceding slow twitch fibre hypertrophy. Whilst some indirect measures of fibre number in living humans suggest that there is no interindividual variation, postmortem evidence suggests that there is. There are also animal data arising from investigations using resistance training protocols which suggest that chronic exercise can increase fibre number. Furthermore, satellite cell activity has been linked to myotube formation in the human. However, other animal models (i.e. compensatory hypertrophy) do not support the notion of fibre hyperplasia. Even if hyperplasia does occur, its effect on the cross-sectional area of muscle appears to be small. Phosphagen and glycogen metabolism, whilst important during resistance activity appear not to normally limit the performance of resistance activity. Phosphagen and related enzyme adaptations are affected by the type, structure and duration of resistance training. Whilst endogenous glycogen reserves may be increased with prolonged training, typical isotonic training for less than 6 months does not seem to increase glycolytic enzyme activity. Lipid metabolism may be of some significance in bodybuilding type activity. Thus, not surprisingly, oxidative enzyme adaptations appear to be affected by the structure and perhaps the modality of resistance training. The dilution of mitochondrial volume and endogenous lipid densities appears mainly because of fibre hypertrophy.

Seasonal variation of selected performance parameters in épée fencers

In this study, anthropometric measurements were carried out on seven British international male épée fencers, using a maximal treadmill running test, a 20-s Wingate-type test, and isokinetic dynamometry. Testing was conducted on two occasions, 5 to 6 months apart, during mid-off-season (preparation) and mid-in-season (competition) periods. Maximal oxygen intake (VO2max) and maximal respiratory exchange ratio (Rmax) were among the parameters obtained from the treadmill test, while peak and mean anaerobic power outputs were measured during a 20-s maximal effort. Knee extensor and flexor muscle forces from both dominant (leading) and non-dominant (trailing) legs were assessed at 1.04, 3.14 and 4.19 rad sec-1. Statistical analyses revealed lower mean VO2max (P < 0.05) and mean Rmax values (P < 0.02) at the in-season assessments compared with off-season. In-season testing also demonstrated significantly lower peak torques for both dominant and non-dominant knee extensors compared with off-season assessments at all velocities (P < 0.05 to P < 0.004). Furthermore, in-season peak torque for the non-dominant leg flexors was lower (P < 0.03) at 4.19 rad sec-1 than off-season. We conclude that current training practices may account for the observed seasonal variations in performance related physiological parameters in fencers.

Increase in the proportion of fast-twitch muscle fibres by sprint training in males

Fifteen male physical education students were studied. The subjects trained for 4-6 weeks, 2-3 days per week, on a mechanically braked bicycle ergometer. A training session consisted of repeated 30-s 'all-out' sprints on a Wingate bicycle ergometer, on which the brake band of the flywheel was loaded with 75 g kg-1 body wt, with rest periods of 15-20 min between consecutive sprints. Thigh muscle biopsies were taken before and after the training period and were analysed for fibre types using a myofibrillar ATPase stain. The proportion of type I fibres decreased from 57 to 48% (P less than 0.05) and type IIA fibres increased from 32 to 38% (P less than 0.05). This study indicates that it is possible to achieve a fibre type transformation with high-intensity training. The effect of two-legged 'sprint' training on muscle fibre type composition may be related to a changed pattern of muscle fibre activation (e.g. an increased stimulation frequency). A change in fibre activation frequency may induce an increased synthesis of type II fibre myosin (fast myosin). Hormonal influences such as enhanced adrenergic stimulation of the muscle fibres cannot be excluded as a contributing factor, however.

The effect of hypoxia on performance during 30 s or 45 s of supramaximal exercise

The purpose of this study was to evaluate the effect of hypoxia (10.8 +/- 0.6% oxygen) on performance of 30 s and 45 s of supramaximal dynamic exercise. Twelve males were randomly allocated to perform either a 30 s or 45 s Wingate test (WT) on two occasions (hypoxia and room air) with a minimum of 1 week between tests. After a 5-min warm-up at 120 W subjects breathed the appropriate gas mixture from a wet spirometer during a 5-min rest period. Resting blood oxygen saturation was monitored with an ear oximeter and averaged 97.8 +/- 1.5% and 83.2 +/- 1.9% for the air (normoxic) and hypoxic conditions, respectively, immediately prior to the WT. Following all WT trials, subjects breathed room air for a 10-min passive recovery period. Muscle biopsies from the vastus lateralis were taken prior to and immediately following WT. Arterialized blood samples, for lactate and blood gases, were taken before and after both the warm-up and the performance of WT, and throughout the recovery period. Open-circuit spirometry was used to calculate the total oxygen consumption (VO2), carbon dioxide production and expired ventilation during WT. Hypoxia did not impair the performance of the 30-s or 45-s WT. VO2 was reduced during the 45-s hypoxic WT (1.71 +/- 0.21 l) compared with the normoxic trial (2.16 +/- 0.26 l), but there was no change during the 30-s test (1.22 +/- 0.11 vs 1.04 +/- 0.17 l for the normoxic and hypoxic conditions, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a task-specific warm-up on anaerobic power

Twenty-four untrained (UT) males (age 21 +/- 2.5 yr, height 1.77 +/- 0.05 m, weight 75.3 +/- 10.1 kg, values mean +/- SD) performed the Wingate Anaerobic Test (WT) under two conditions, cold (C) and following a warm-up (WU). Trials were separated by a minimum of 48 h. A modified Monark 818 cycle ergometer was interfaced with an Apple IIE microcomputer and peak power (PEAK), mean power (MEAN) and fatigue index (FI) determined. The WU trial consisted of an 8 min incremental continuous cycling bout (cadence 90 rev.min-1) with 5 min rest before the WT. During the C trial subjects completed only the WT. A repeated measures design was employed with order of trials counterbalanced. ANOVA revealed no significant differences for PEAK or MEAN between WU or C conditions. However FI was significantly greater (p less than 0.05) following the WU. A significant correlation (r = 0.45, p = 0.03) was obtained between WU intensity and FI. These findings suggest that our UT subjects were fatiguing themselves during the WU. Future studies are needed to assess whether a task-specific WU in which FI is not impaired would lead to improvements in PEAK and MEAN. Investigators should be aware that a self-spaced WU may increase FI in the WT in UT subjects.

Effect of sodium bicarbonate ingestion upon repeated sprints

The purpose of the study was to assess the effect of sodium bicarbonate ingestion upon repeated bouts of intensive short duration exercise. Twenty-three subjects participated in the investigation (8 females and 15 males, age 21.4 +/- 2.3, mean +/- sd). Subjects completed six trials; three following the ingestion of sodium bicarbonate (300 mg/kg body weight) and three following the ingestion of a placebo (8 g sodium chloride). Each trial consisted of ten ten-second sprints on a cycle ergometer with 50 seconds recovery between each sprint. 'Peak power' and 'average power output' during each ten second sprint was measured from the flywheel of the ergometer using a light-sensitive monitor (Cranlea) linked to a BBC microcomputer. The power outputs recorded during each ten-second sprint of the bicarbonate trials were then compared with those recorded during the corresponding sprint of the placebo trials. The bicarbonate trials produced higher mean 'average power' outputs in all ten of the ten-second sprints, with the difference in 'average power' output being statistically significant in eight of these (p less than 0.05). The results also revealed that the difference in the 'average power' outputs attained during the bicarbonate and placebo trials increased as the number of sprint repetitions increased (p less than 0.01). 'Peak power' output was also greater in the bicarbonate trials with it being significantly higher (p less than 0.001) during the final ten-second sprint. It was concluded that during exercise consisting of repeated, short-duration sprints, power output was enhanced following the ingestion of sodium bicarbonate, (300 mg/kg body weight).

ATP and IMP in single human muscle fibres after high intensity exercise

Within a muscle there is large variation in the activity of various enzymes among single fibres. It is reasonable, therefore, to expect a corresponding variation in their metabolic response to exercise. This was examined by obtaining muscle biopsies from five men at rest and after intense short-term exercise consisting of three bouts of 30 knee extensions each and intervened by 60 s rest. Freeze-dried dissected single fibres identified as type 1 or type 2 were analysed for ATP and IMP contents by liquid chromatography. Rest. Average ATP tended to be higher in type 2 than in type 1 fibres. The ATP range was 14-30 and 14-32 mmol X kg-1 dry muscle (dm) in type 1 and 2 fibres, respectively. IMP was less than 1 mmol X kg-1 dm in most fibres and similar in types 1 and 2. Exercise. Muscle force decreased 70% during exercise. The average decrease in ATP content was significant for both fibre types with somewhat larger response for type 2 (20%) than type 1 (10%) fibres. The ATP range was 10-28 and 10-30 mmol X kg-1 dm in type 1 and 2 fibres, respectively. Average IMP content increased substantially in both fibre types, more so for type 2, and the range for individual fibres was 0-13 (type 1) and 0-21 (type 2) mmol X kg-1 dm. Conclusion. After exhaustive short-term exercise, a large variation in ATP and IMP contents was evident among single type 1 and type 2 fibres. None of the fibres, however, showed an ATP content lower than 10 mmol X kg-1 dm.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood lactate. Implications for training and sports performance

The blood lactate response to exercise has interested physiologists for over fifty years, but has more recently become as routine a variable to measure in many exercise laboratories as is heart rate. This rising popularity is probably due to: the ease of sampling and improved accuracy afforded by recently developed micro-assay methods and/or automated lactate analysers; and the predictive and evaluative power associated with the lactate response to exercise. Several studies suggest that the strong relationship between exercise performance and lactate-related variables can be attributed to a reflection by lactate during exercise of not only the functional capacity of the central circulatory apparati to transport oxygen to exercising muscles, but also the peripheral capacity of the musculature to utilise this oxygen. For example, several studies contrast the relationship between VO2max and endurance running performance with that between a lactate variable and the same running performance. In every study, the lactate variable is more highly correlated with performance. Similarly, prescribing training intensity as a function of the lactate concentration elicited by the training may prove to be a means of obtaining a more homogeneous adaptation to training in a group of athletes or subjects than is obtained by setting intensity as a function of maximal heart rate or % VO2max. A review of the recent literature shows that the lactate response to supramaximal exercise is a sensitive indicator of adaptation to 'sprint training' and is correlated with supramaximal exercise performance. This review also describes the possible applications of lactate measurements to enhance the rate of recovery from high intensity exercise. Although the lactate response to exercise is reproducible under standardised conditions it can be influenced by the site of blood sampling, ambient temperature, changes in the body's acid-base balance prior to exercise, prior exercise, dietary manipulations, or pharmacological interpretation.