The health benefits of rooibos tea in humans (aspalathus linearis)-a scoping review.

Natural remedies in the treatment of health conditions are an appealing option for many individuals. Previous studies reported that fermented and unfermented rooibos tea have considerable anti-inflammatory and antioxidative properties. Most of this knowledge, however, originates from animal and cell culture studies. The aims of this review are to evaluate the existing, but limited, body of knowledge regarding rooibos tea interventions in humans and to identify the gaps in the literature. The PRISMA extension for Scoping Reviews (PRISMA-ScR) guidelines were followed in the collation of this scoping review. Among the databases searched were Google Scholar, PubMed, Cochrane Library, Scopus, and Web of Science. This review comprised 18 publications, with half (50%) of the studies being conducted in South Africa. There were 488 participants in all, ranging in age from six to 83 years, in the investigations. Rooibos tea was either fermented, unfermented, or black in 62% of the studies. Doses ranging from 200 to 1,200 ml were employed. In both healthy and at-risk individuals, rooibos has been shown to enhance lipid profiles, boost antioxidant status, and lower blood glucose levels. The existing findings suggests that rooibos consumption demonstrated to improve lipid profiles, boost antioxidant status, and lower blood glucose levels in both apparently healthy, and individual at-risk individuals or diagnosed of chronic conditions. Thus, it can be presumed that rooibos tea provides some health benefits, yet these findings are based on a limited number of human intervention studies and a small total sample size. Additionally, a variety of rooibos dosages and types of tea in the experiments had inconsistent results that were probably impacted by the amount consumed. Future studies should include a dose-response study in humans, as well as large scaled clinical trials to evaluate the health effects of Rooibos.

Physical activity promotion in persons with spinal cord injuries: Barriers and facilitators in low-resource communities.

Background: A spinal cord injury is a devastating and life-changing event that presents the affected individual with multiple challenges throughout life. Physical activity can help mitigate some of these challenges; however, in low-resource communities where opportunities for physical activity are scarce, these challenges are often exacerbated and multiple. Objective: This study aimed to identify the barriers and facilitators to physical activity, specifically in individuals with spinal cord injuries, in low-resourced communities. Methods: A total of 57 adults (> 20 years) with a spinal cord injury living in the Western Cape, South Africa completed the self-developed research questionnaire. Results: A total of 289 barriers and 290 facilitators were reported. The most frequently reported barriers were lack of transport (n = 35), impairment type (n = 32), lack of trained volunteers and appropriate programmes (n = 19 each) and lack of information received from therapists following discharge (n = 10). The most frequently reported facilitators were support from family (n = 38), the 'enjoyment' of physical activity and the fact that 'it made me feel good' (n = 37); safe and accessible facilities were reported by 25 participants and 12 participants reported that higher-quality programmes and better-trained staff would help them to be more physically active. Conclusion: Individuals with a spinal cord injury face many barriers in being physically active. Yet it is evident that people with spinal cord injuries in low-resourced communities are eager to participate and improve their health and physical function. However, this will only realise if practitioners reduce the barriers to access, provide relevant training to staff and volunteers, educate their patients about the importance of physical activity post discharge, and create tailored programmes in safe and accessible community facilities.

Combined protein and calcium ß-hydroxy-ß-methylbutyrate induced gains in leg fat free mass: a double-blinded, placebo-controlled study.

BACKGROUND: The leucine metabolite ß-hydroxy-ß-methylbutyrate (HMB) is widely used as an ergogenic supplement to increase resistance-training induced gains in fat free mass (FFM) and strength in healthy adults. Recent studies have questioned the effectiveness of HMB, particularly when a high protein diet is habitually consumed. To investigate the additive resistance-training induced effects of HMB and protein in untrained individuals, we conducted a randomized double-blind, placebo-controlled study that compared the effects of combined protein and HMB supplementation to protein supplementation alone on FFM and muscle strength after 12-week resistance training. METHODS: Sixteen healthy men (22 ± 2 yrs) performed a periodized resistance-training program for twelve weeks (four sessions per week). The program comprised two mesocycles, characterized by a linear periodization and non-linear periodization, respectively, and separated by a 1-week tapering period. All participants received 60 g of whey protein on training days and 30 g of whey protein (WP) on non-training days. Participants were randomly assigned to additionally receive 3 g of calcium HMB (WP + HMB) or a placebo (WP + PLA). Body composition and physical fitness were tested before and after the 12-week training program. Whole-body and arm and leg fat free mass (FFM) were assessed by bioimpedance spectroscopy; upper arm and leg fat free cross sectional areas were also quantified using magnetic resonance imaging (MRI); upper and lower body strength were measured by One-repetition maximum (1-RM) bench press and leg press. RESULTS: Whole-body and segmental FFM increased in both groups (P <  0.001). However, gains in leg FFM were higher in WP + HMB vs. WP + PLA (arm FFM: + 6.1% vs. + 9.2%, P = 0.2; leg FFM: + 14.2% vs. + 7.0%, P <  0.01). No change in fat mass was observed (P = 0.59). 1-RM increased in both groups (P <  0.001). CONCLUSIONS: Combined protein and HMB supplementation resulted in segmental, but not whole-body increases in FFM compared to protein supplementation alone. These findings could explain some of the controversial effects of HMB reported in previous studies and have practical implications for maximizing training-induced gains in FFM and clinical conditions associated with skeletal muscle deconditioning such as aging, sedentary lifestyles, bed rest and spaceflight.

Body composition and somatotypes of male Zimbabwean Premier League football referees.

BACKGROUND: Elite athletes need to optimize their body composition to deliver world class performances and this argument could be extended to elite referees as well. Unfortunately, there is a scarcity of body composition information among football referees. The aim of the study was to determine and compare the body composition and somatotypes of male football referees and assistant referees who officiated in the 2013 Zimbabwe Premier Football League. METHODS: Forty-one participants (21 referees, 20 assistant referees; 8 FIFA, 33 ZIFA licensed referees) with a mean age of 34.89±5.13 years took part. They had on average 10.85±3.85 years of refereeing experience. The ISAK restricted anthropometric profile was used to measure body mass, height, skinfolds, girths and bone breadths, from which Body Mass Index (BMI), waist-to-hip ratio (WHR), percentage body fat and somatotype were calculated. RESULTS: The referees were significantly taller than the assistant referees. The FIFA referees had moderately more desirable anthropometric profiles than the ZIFA referees. With a mean somatotype of 2.62-4.65-2.65, the total sample could be classified as balanced mesomorphs. They had lower BMI and body fat percentages than that observed among referees from other nationalities in the available literature. CONCLUSIONS: The results add to the paucity of information on the body composition of football officials. Referees aiming to excel at higher levels need to obtain and maintain an ideal body composition since elite level football is intense and requires high fitness levels.

Physiological performance predictors in mountain bike multi-stage races.

BACKGROUND: This study set out to identify physiological variables that may predict performance in The Cape Epic, an 8-day multi-stage mountain bike (MTB) race held annually in South Africa. METHODS: Twenty-four amateur riders underwent VO2max testing within the 8 weeks prior to the event. Blood lactate measurements were taken to determine the power output corresponding to a fixed lactate concentration of 2 (LT2) and 4 mmol/L (OBLA) during the incremental test. Total race time was selected as dependent variable. RESULTS: Absolute power output at LT2 (POLT2) had the strongest correlation (r=-0.80; CI: -0.91 to -0.59) with total race time. In general, absolute physiological variables, compared with relative values, correlated more favorably with total race time, suggesting that body mass may be of lesser importance in these longer events. Relative correlations were stronger when normalized to an exponent of 0.79. The correlations for VO2max and end maximal lactate with total race time were negligible (r=-0.14, CI: -0.51 to 0.28); r=0.03, CI: -0.32 to 0.43). CONCLUSIONS: The findings of this study emphasize the importance of a well-developed aerobic system in multi-day MTB stage races and that riders should focus on developing a high sustainable sub maximal power output in order to complete the race in the shortest possible time.

The effect of three different exercise training modalities on cognitive and physical function in a healthy older population.

BACKGROUND: Older adults are encouraged to participate in regular physical activity to counter the age-related declines in physical and cognitive health. Literature on the effect of different exercise training modalities (aerobic vs resistance) on these health-related outcomes is not only sparse, but results are inconsistent. In general, it is believed that exercise has a positive effect on executive cognitive function, possibly because of the physiological adaptations through increases in fitness. Indications are that high-intensity interval training is a potent stimulus to improve cardiovascular fitness, even in older adults; however, its effect on cognitive function has not been studied before. Therefore, the purpose of this study was to compare the effects of resistance training, high-intensity aerobic interval training and moderate continuous aerobic training on the cognitive and physical functioning of healthy older adults. METHODS: Sixty-seven inactive individuals (55 to 75 years) were randomly assigned to a resistance training (RT) group (n = 22), high-intensity aerobic interval training (HIIT) group (n = 13), moderate continuous aerobic training (MCT) group (n = 13) and a control (CON) group (n = 19) for a period of 16 weeks. Cognitive function was assessed with a Stroop task and physical function with the Timed-Up-and-Go (TUG) and submaximal Bruce treadmill tests. RESULTS: No significant GROUP x TIME interaction was found for Stroop reaction time (P > .05). The HIIT group showed the greatest practical significant improvement in reaction time on the information processing task, i.e. Stroop Neutral (ES = 1.11). MCT group participants had very large practical significant improvements in reaction time on the executive cognitive tasks, i.e. Stroop Incongruent and Interference (ES = 1.28 and 1.31, respectively). The HIIT group showed the largest practically significant increase in measures of physical function, i.e. walking endurance (ES = 0.91) and functional mobility (ES = 0.36). CONCLUSIONS: MCT and RT proved to be superior to HIIT for the enhancement of older individuals' executive cognitive function; whereas HIIT were most beneficial for improvement in information processing speed. HIIT also induced the largest gains in physical function.

Cerebral oxygenation during cortical activation: the differential influence of three exercise training modalities. A randomized controlled trial.

PURPOSE: To determine if a cerebral oxygenation response during cortical activation is influenced by exercise training mode. METHODS: Sixty-seven individuals (55-75 years old) volunteered for this 16-week intervention study. Participants were randomized into a resistance training (RT) group (n = 22), high-intensity interval training (HIIT) group (n = 13), moderate continuous training (MCT) group (n = 13) and a control (CON) group (n = 19). Near-infrared spectroscopy was used to measure cerebral oxygenation during the Stroop task. A submaximal Bruce treadmill test was used to measure changes in walking endurance. RESULTS: The GROUP × TIME interaction for reaction time on the naming and executive Stroop conditions were not significant (P > 0.05). At post-test, the CON group showed increased brain activation, with significantly higher relative oxy-haemoglobin (O2Hb) values during the naming Stroop condition compared to pre-test (P = 0.03), while their increased relative O2Hb on the complex condition showed a distinct trend toward significance (P = 0.09). MCT and HIIT participants exhibited decreased brain activation during the Stroop task, with MCT showing a significant increase in relative deoxy-haemoglobin (HHb) compared to pre-test during the naming and executive Stroop conditions (P < 0.05). The HIIT group improved significantly in walking endurance (P = 0.04). CONCLUSION: Sixteen weeks of exercise training resulted in more efficient cerebral oxygenation during cortical activation compared to a no-exercise control group. Furthermore, HIIT and MCT were superior to RT for task-efficient cerebral oxygenation and improved oxygen utilization during cortical activation in older individuals.

Characterisation of the responsive properties of two running-specific prosthetic models.

BACKGROUND: The need for information regarding running-specific prosthetic properties has previously been voiced. Such information is necessary to assist in athletes' prostheses selection. OBJECTIVES: This study aimed to describe the characteristics of two commercially available running-specific prostheses. STUDY DESIGN: The running-specific prostheses were tested (in an experimental setup) without the external interference of athlete performance variations. METHODS: Four stiffness categories of each running-specific prosthetic model (Xtend™ and Xtreme™) were tested at seven alignment setups and three drop masses (28, 38 and 48 kg). Results for peak ground reaction force (GRFpeak), contact time ( tc), flight time ( tf), reactive strength index (RSI) and maximal compression (Δ L) were determined during controlled dropping of running-specific prostheses onto a force platform with different masses attached to the experimental setup. RESULTS: No statistically significant differences were found between the different setups of the running-specific prostheses. Statistically significant differences were found between the two models for all outcome variables (GRFpeak, Xtend > Xtreme; tc, Xtreme > Xtend; tf, Xtreme > Xtend; RSI, Xtend > Xtreme; Δ L, Xtreme > Xtend; p < 0.05). CONCLUSION: These findings suggest that the Xtreme stores more elastic energy than the Xtend, leading to a greater performance response. The specific responsive features of blades could guide sprint athletes in their choice of running-specific prostheses. Clinical relevance Insights into the running-specific prosthesis (RSP) properties and an understanding of its responsive characteristics have implications for athletes' prosthetic choice. Physiologically and metabolically, a short sprint event (i.e. 100 m) places different demands on the athlete than a long sprint event (i.e. 400 m), and the RSP should match these performance demands.

The training and detraining effect of high-intensity interval training on post-exercise hypotension in young overweight/obese women.

PURPOSE: Studies evaluating the response in blood pressure (BP) following high-intensity interval training (HIIT) are scant even though there has been extensive work done on the BP response following acute and chronic low- to moderate-intensity aerobic and resistance exercise in both hypertensive and normotensive individuals. The present study sought to investigate the training and detraining effects of short-term HIIT on the post-exercise hypotension (PEH) response in overweight/obese young women. METHOD: Twenty young untrained women volunteered for the study. Participants performed six HIIT sessions on a treadmill within 2 weeks (week 1: 10 × 1 min and week 2: 15 × 1 min intervals at 90-95% HRmax, separated by 1 min active recovery at 70% HRmax each session) and detrained for 2 weeks. Post-exercise BP was measured for 1 h following the first and last HIIT sessions. RESULTS: Participants were normotensive (SBP: 119.2 ± 5.60 mmHg; DBP: 78.8 ± 4.12 mmHg) and had a BMI greater than 25 kg m(-2). The magnitude of the systolic hypotensive response was slightly greater after the six sessions HIIT compared to pre-training (5.04 and 4.28 mmHg, respectively), and both would be considered clinically significant (>3 mmHg decrease). After 2 weeks, detraining the PEH response was not clinically significant (1.08 mmHg decrease). The magnitude of the DBP response was only clinically significant following post- and detraining (4.26 and 3.87 mmHg, respectively). CONCLUSION: The findings suggest that six HIIT sessions is sufficient to affect clinically significant PEH responses in young, overweight/obese women; however, the training effects are lost within 2 weeks of detraining.

Paralympic Sprint Performance Between 1992 and 2012.

UNLABELLED: The Paralympic Games have undergone many changes since their inception in 1960, one being the advances made in running-specific prostheses (RSPs) for track athletes with lower-limb amputations. PURPOSE: To investigate the sprinting-performance changes in athletes with lower-limb amputations since 1992 to assess whether the influence of developments in RSP technology is evident. METHODS: The results of the Olympic and Paralympic Games ranging between 1992 and 2012 for the 100-m and 200-m were collected, and performance trends, percentage change in performance, and competition density (CD) were calculated. RESULTS: The results indicate that the greatest performance increases were seen in athletes with lower-limb amputations (T42 = 26%, T44 = 14%). These performance improvements were greater than for Olympic athletes (<3%), as well as Paralympic athletes from other selected classes (<10%). The T42 and T44 classes also showed the lowest CD values. DISCUSSION: These results suggest that although there is an overall trend for improved Paralympic sprint performances, RSP technology has played a noteworthy role in the progression of performances of athletes with amputations. It is also hypothesized that the difference in the performance improvements between the T42 and T44 classes is due to the level of disability and therefore the extent to which technology is required to enable locomotion. CONCLUSION: It is evident that RSP technology has played a significant role in the progression of performances in athletes with lower-limb amputations.

The time course of changes induced by resistance training and detraining on muscular and physical function in older adults.

BACKGROUND: It is generally recognised that the physical functioning of older adults is enhanced with resistance exercise. The aim of this study was to investigate the time course of changes in upper and lower body muscle strength and physical function in older individuals following a 16 week resistance training (RT) programme and a similar duration detraining (DET) period. METHODS: Forty-one inactive individuals (55 to 75 years) were randomly allocated in a RT group (n = 22; three sessions per week) and a control (CON) group (n = 19). Muscle strength was assessed with 10RM leg and bench press tests, while the Timed-Up-and-Go (TUG) test was used to measure functional mobility. The Bruce treadmill test determined the participants' submaximal endurance capacity. Data were analysed using mixed model repeated measures ANOVA and P < 0.05 was considered statistically significant. RESULTS: Main treatment effects were found for muscle strength (P < 0.001) and functional mobility (P < 0.05). Upper and lower body strength generally showed a statistically significant improvement after every 4 weeks in RT (the increase after 16 weeks being 7.3 ± 4.9 kg and 86.6 ± 44.4 kg, respectively; P < 0.001) while TUG performance (-0.2 ± 0.4 s; P < 0.05) and submaximal endurance capacity (0.7 ± 0.9 min; P < 0.001) only improved after 16 weeks. Although muscle strength decreased after DET, it was still better than at baseline. No significant improvements in any performance variable were observed in CON directly after the intervention period (0-16 weeks) (P > 0.05). CONCLUSION: A 16-week RT programme has positive effects on both muscular and physical function in older adults, although the time course of these adaptations is different. While the gains in muscle strength and submaximal endurance capacity were not totally lost after DET, functional mobility was completely reversed. Older adults can be reassured that if the need arises to discontinue RT for a certain period they will still retain a large amount of their acquired muscle strength, as well as a degree of physical function such as submaximal endurance capacity. The association between leg strength and submaximal endurance capacity strengthens the notion that RT should be incorporated in training and rehabilitation programmes of ageing and frail older adults.

The influence of sprint interval training on body composition, physical and metabolic fitness in adolescents and young adults with intellectual disability: a randomized controlled trial.

OBJECTIVE: In this study we evaluated the effect of sprint interval training on metabolic and physical fitness in adolescents and young adults with intellectual disabilities when compared with continuous aerobic training and no training (control). METHODS: Fifty-four persons with intellectual disabilities (age: 17 (3.0), body mass index: 27.7 (3.7), intelligence quotient: 59 (8.6)) were matched based on age, gender and intelligence quotient between sprint interval training (n = 17), continuous aerobic training (n = 15) and control (n = 14). Sprint interval training was composed of three blocks of 10 minutes at ventilatory threshold (blocks 1 and 3: 10 sprint bouts of 15 seconds, followed by 45 seconds relative rest; block 2: continuous training) twice a week for 15 weeks. Continuous aerobic training was composed of three blocks of 10 minutes continuous training. After eight weeks, intensity was increased to 110% of ventilatory threshold. The control group did not participate in supervised exercise training. Before and after the training period, body composition, physical and metabolic fitness were evaluated. RESULTS: Sprint interval training showed a significant positive evolution for waist circumference, fat%, systolic blood pressure, lipid profile, fasting insulin, homeostasis model assessment of insulin resistance, peak VO2, peak Watt, ventilatory threshold, 6-minute walk distance and muscle fatigue resistance when compared with no training (P < 0.01). The sprint interval training group demonstrated significant improvements for fat%, systolic blood pressure, low-density lipoprotein, fasting insulin, peak VO2 and peak power and ventilatory threshold (P < 0.01) when compared with continuous aerobic training. CONCLUSION: In this study we could observe that sprint interval training has stronger beneficial effects on body composition, physical fitness and metabolic fitness compared with control. Compared with continuous aerobic training, sprint interval training seems to result in better outcome.

The magnitude and duration of post-exercise hypotension after land and water exercises.

The objective of the study was to determine and compare the magnitude and duration of post-exercise hypotension (PEH) during free-living conditions after an acute session of concurrent water and land exercise in individuals with prehypertension and hypertension. Twenty-one men and women (aged 52 ± 10 years) volunteered for the study. Participants completed a no exercise control session, a water exercise session and a land exercise session in random order. After all three sessions, participants underwent 24-h monitoring using an Ergoscan ambulatory BP monitoring device. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were monitored to determine changes from resting values after each session and to compare the PEH responses between land and water exercises. During daytime, both land and water exercises resulted in significantly lower SBP (12.7 and 11.3 mmHg) compared to the control session (2.3 mmHg). The PEH response lasted for 24 h after land exercise and 9 h after water exercise. There was no difference in the daytime DBP for the three treatments (P > 0.05). Although all three groups showed significant reductions during nighttime, both exercise treatments showed greater nocturnal falls in BP than the control treatment. This is the first study to show that the magnitude of the PEH response is similar for land and water exercises, although the duration of PEH may be longer for land exercise. These results suggest that water exercise is a safe alternative exercise modality for individuals with suspected and known hypertension.

The kinanthropometric and pulmonary determinants of global respiratory muscle strength and endurance indices in an athletic population.

The morphological determinants of respiratory muscle (RM) strength and endurance in non-athletic populations are well documented, but are lacking in athletic populations. The purpose of this study was to determine the kinanthropometric and pulmonary predictors of RM strength and endurance. 160 athletes (103 men) were recruited from eight different sports to participate in the study. All subjects underwent a series of kinanthropometric and RM function assessments during a single visit to the laboratory. RM function assessments included the flow-volume curve test to assess pulmonary function, maximum voluntary ventilation (MVV) to assess RM endurance and maximum inspiratory mouth pressure (MIP) and maximum expiratory mouth pressure (MEP) to assess RM strength. Multiple regression analyses revealed that gender, mesomorphy and exercise sessions per week predicted 35% (SEE = 26.6 cmH(2)O) of the variance in inspiratory muscle strength (MIP). Gender and mesomorphy predicted 24% (SEE = 28.3 cmH(2)O) of the variance in expiratory muscle strength (MEP), while gender, relative sitting height, forced expiratory volume in 1 s (FEV(1)) and peak expiratory flow rate (PEFR) predicted 78% (SEE = 18.2 L min(-1)) of the variance in RM endurance (MVV). Although the reference equations are still not adequate to predict MIP and MEP in an athletic population, they provide more suitable reference values than previously reported. The predicted values derived from the equation for MVV can be applied as adequate reference values for athletic populations.

VO(2max) prediction from multi-frequency bioelectrical impedance analysis.

Bioelectrical impedance analysis (BIA) has been shown to be highly related to skeletal muscle mass and blood volume, both of which are important determinants of maximal oxygen uptake (VO(2max)). The aim of the present study was therefore to investigate the ability of whole-body and segmental multi-frequency BIA to improve current nonexercise VO(2max) prediction models. Data for VO(2max) (mL min(-1)), anthropometry, self-reported physical activity (PA-R) and BIA were collected in 115 men and women. Multiple linear regression analysis (MLR) was used to develop the most parsimonious prediction model. Segmental BIA was not superior to whole-body measurements. Correlation coefficients between VO(2max) and resistance indices were significantly higher at 500 kHz compared to 50 kHz (p < 0.05). Intracellular resistance index, however, showed the highest correlation with VO(2max) (r = 0.89). After adjusting for age, gender and PA-R, MLR revealed that the inclusion of intracellular resistance index was slightly, but significantly (p < 0.001), superior to models based on anthropometry. Subgroup analyses indicated that the true benefit of BIA might be most prevalent in subjects with particularly low VO(2max) (<2500 mL min(-1)). In short, whole-body BIA marginally improves the accuracy of nonexercise VO(2max) prediction models and its advantage is most pronounced in individuals with particularly low VO(2max).

Modeling upper and lower limb muscle volume by bioelectrical impedance analysis.

Most studies employing bioelectrical impedance analysis (BIA) for estimating appendicular skeletal muscle mass using descriptive BIA models rely on statistical rather than biophysical principles. The aim of the present study was to evaluate the feasibility of estimating arm and leg muscle volume (MV) based on multiple bioimpedance measurements and using a recently proposed mathematical model and to compare this technique to conventional segmental BIA at high and low frequencies. MV of the arm and leg, respectively, was determined in 15 young, healthy, active men [age 22 +/- 2 (SD) yr, total body fat 15.6 +/- 5.1%] by magnetic resonance imaging (MRI) and BIA using a conventional and new bioimpedance model. MRI-determined MV for leg and arm was 6,268 +/- 1,099 and 1,173 +/- 172 cm(3), respectively. Estimated MV by the new BIA model [leg: 6,294 +/- 1,155 cm(3) (50 kHz), 6,278 +/- 1,103 cm(3) (500 kHz); arm: 1,216 +/- 172 cm(3) (50 kHz), 1,155 +/- 157 cm(3) (500 kHz)] was not statistically different from MRI-determined MV (leg: P= 0.958; arm: P= 0.188). The new BIA model was superior to conventional BIA and performed best at 500 kHz for estimating leg MV as indicated by the lower relative total error [new: 3.6% (500 kHz), 5.2% (50 kHz); conventional: 7.6% (500 kHz) and 8.3% (50 kHz)]. In contrast, the new BIA model, both at 50 and 500 kHz, did not improve the accuracy for estimating arm MV [new: 10.8% (500 kHz), 10.6% (50 kHz); conventional: 11.8% (500 kHz), 11.4% (50 kHz)]. It was concluded that modeling of multiple BIA measurements has advantages for the determination of lower limb muscle volume in healthy, active adult men.

Field and laboratory correlates of performance in competitive cross-country mountain bikers.

We designed a laboratory test with variable fixed intensities to simulate cross-country mountain biking and compared this to more commonly used laboratory tests and mountain bike performance. Eight competitive male mountain bikers participated in a cross-country race and subsequently did six performance tests: an individual outdoor time trial on the same course as the race and five laboratory tests. The laboratory tests were as follows: an incremental cycle test to fatigue to determine peak power output; a 26-min variable fixed-intensity protocol using an electronically braked ergometer followed immediately by a 1-km time trial using the cyclist's own bike on an electronically braked roller ergometer; two 52-min variable fixed-intensity protocols each followed by a 1-km time trial; and a 1-km time trial done on its own. Outdoor competition time and outdoor time trial time correlated significantly (r = 0.79, P < 0.05). Both outdoor tests correlated better with peak power output relative to body mass (both r = -0.83, P < 0.05) than absolute peak power output (outdoor competition: r = -0.65; outdoor time trial: r = -0.66; non-significant). Outdoor performance times did not correlate with the laboratory tests. We conclude that cross-country mountain biking is similar to uphill or hilly road cycling. Further research is required to design sport-specific tests to determine the remaining unexplained variance in performance.

Estimation of maximal oxygen uptake by bioelectrical impedance analysis.

Previous non-exercise models for the prediction of maximal oxygen uptake VO(2max) have failed to accurately discriminate cardiorespiratory fitness within large cohorts. The aim of the present study was to evaluate the feasibility of a completely indirect method for predicting VO(2max) that was based on bioelectrical impedance analysis (BIA) in 66 young, healthy fit men and women. Multiple, stepwise regression analysis was used to determine the usefulness of BIA and additional covariates to estimate VO(2max) (ml min(-1)). BIA was highly correlated to VO(2max) (r = 0.914; P < 0.001) and entered the regression equation first. The inclusion of gender and a physical activity rating further improved the model which accounted for 88% of the variance in VO(2max) and resulted in a relative standard error of the estimate (SEE) of 7.2%. Substantial agreement between the methods was confirmed by the fact that nearly all the differences were within +/-2 SD. Furthermore, in contrast to previously published non-exercise models, no trend of a reduction in prediction accuracy with increasing VO(2max) values was apparent. It was concluded that a non-exercise model based on BIA might be a rapid and useful technique to estimate VO(2max), when a direct test does not seem feasible. However, though the present results are useful to determine the viability of the method, further refinement of the BIA approach and its validation in a large, diverse population is needed before it can be applied to the clinical and epidemiological settings.

Evolution of cooperation: cooperation defeats defection in the cornfield model.

"Cooperation" defines any behavior that enhances the fitness of a group (e.g. a community or species), but which, by its nature, can be exploited by selfish individuals, meaning, firstly, that selfish individuals derive an advantage from exploitation which is greater than the average advantage that accrues to unselfish individuals. Secondly, exploitation has no intrinsic fitness value except in the presence of the "cooperative behavior". The mathematics is described by the simple Prisoner's Dilemma Game (PDG). It has previously been shown that koinophilia (the avoidance of sexual mates displaying unusual or atypical phenotypic features, such as mutations) stabilizes any inherited strategy in the simple or iterated PDG, meaning that it cannot be displaced by rare forms of alternative behavior which arise through mutation or occasional migration. In the present model equal numbers of cooperators and defectors (in the simple PDG) were randomly spread in a two-dimensional "cornfield" with uniformly distributed resources. Every individual was koinophilic, and interacted (sexually and in the PDG tournaments) only with individuals from within its immediate neighborhood. This model therefore tested whether cooperation can outcompete defection or selfishness in a straight, initially equally matched, evolutionary battle. The results show that in the absence of koinophilia cooperation was rapidly driven to extinction. With koinophilia there was a very rapid loss of cooperators in the first few generations, but thereafter cooperation slowly spread, ultimately eliminating defection completely. This result was critically dependent on sampling effects of neighborhoods. Small samples (resulting from low population densities or small neighborhood sizes) increase the probability that a chance neighborhood comes to consist predominantly of cooperators. A sexual preference for the most common phenotype in the neighborhood then makes that phenotype more common still. Once this occurs cooperation's spread becomes almost inevitable.