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Biomedical subjects

M I Lambert

Publications and source records attributed to M I Lambert.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of maximal exercise performance, fatigue, and depression in athletes with acquired chronic training intolerance.

OBJECTIVE: This study compared differences in maximal strength and aerobic capacity and symptoms of fatigue and depression in athletes with acquired training intolerance (ATI) and control athletes (CON) matched for age and current training volume who did not have symptoms of excessive or chronic fatigue associated with their sporting activity. SETTING: University of Cape Town, Sports Science Institute of South Africa. PARTICIPANTS: Twenty ATI and 10 CON athletes participated in the trial. Although the ATI athletes reported symptoms of excessive fatigue during exercise, or symptoms of fatigue that occurred at rest and during activities of daily living, they did not fulfill the criteria for a diagnosis of chronic fatigue syndrome. MAIN OUTCOME MEASURES: A training and comprehensive medical history was recorded from all subjects. The Beck Depression Inventory Short Form (BDI-SF) was used to assess levels of depression in both ATI and control subjects. Maximal force output during a 5-second isometric voluntary knee extensor muscle contraction, and maximal aerobic capacity (VO2max), maximal heart rate (HRmax), and maximal blood lactate concentrations during a treadmill running test were measured in all subjects. RESULTS: There were no differences in maximal isometric force output, peak treadmill running speed, VO2max, HRmax, or blood lactate concentration at rest or after maximal exercise testing between the ATI and CON athletes. However, the BDI-SF scores were higher in the ATI (7.7 +/- 6.6 arbitrary units) than in the CON athletes (1.7 +/- 1.5 arbitrary units; (P = 0.0052). CONCLUSIONS: These findings suggest that the symptoms of excessive fatigue and acquired training intolerance described by these ATI athletes do not affect their maximal isometric and maximal aerobic capacity, and may be associated with psychologic depression in these athletes.

Adult↗
PubMed2006

Obesity and overweight in South African primary school children -- the Health of the Nation Study.

OBJECTIVES: To determine the prevalence of overweight and obesity in a sample of South African children aged 6 - 13 years. DESIGN: Random sampling of schools within each provincial and socio-economic category. SETTING: Primary school children from 5 South African provinces. SUBJECTS: 10 195 (5 611 male and 4 584 female) primary school children. OUTCOME MEASURE: Height and weight were measured and body mass index (BMI) (weight (kg)/height (m) (2)) was calculated for each grouping (age x gender x ethnic group). Cut-off points for BMI defining obese and overweight for gender and age (6 - 13 years) were calculated in accordance with international standards. RESULTS: There were significant differences in height and mass between the different ethnic groups and genders. This trend was not evident for the BMI values. The prevalence of obesity within the sample was 3.2% for boys and 4.9% for girls, whereas overweight prevalence was 14.0% for boys and 17.9% for girls. When the contribution of each ethnic group was adjusted to the demographics of South Africa these values were only slightly different. The prevalence of obesity and overweight among boys was 2.4% and 10.9% respectively, while obese and overweight girls comprised 4.8% and 17.5%, respectively. CONCLUSIONS: South African children show trends of obesity and overweight, similar to values in developed countries about 10 years ago. Intervention strategies to combat an increasingly sedentary lifestyle may need to be developed for the South African context.

Adolescent↗
PubMed2005

Metabolic setpoint control mechanisms in different physiological systems at rest and during exercise.

Using a number of different homeostatic control mechanisms in the brain and peripheral physiological systems, metabolic activity is continuously regulated at rest and during exercise to prevent catastrophic system failure. Essential for the function of these regulatory processes are baseline "setpoint" levels of metabolic function, which can be used to calculate the level of response required for the maintenance of system homeostasis after system perturbation, and to which the perturbed metabolic activity levels are returned to at the end of the regulatory process. How these setpoint levels of all the different metabolic variables in the different peripheral physiological systems are created and maintained, and why they are similar in different individuals, has not been well explained. In this article, putative system regulators of metabolic setpoint levels are described. These include that: (i) innate setpoint values are stored in a certain region of the central nervous system, such as the hypothalamus; (ii) setpoint values are created and maintained as a response to continuous external perturbations, such as gravity or "zeitgebers", (iii) setpoint values are created and maintained by complex system dynamical activity in the different peripheral systems, where setpoint levels are regulated by the ongoing feedback control activity between different peripheral variables; (iv) human anatomical and biomechanical constraints contribute to the creation and maintenance of metabolic setpoints values; or (v) a combination of all these four different mechanisms occurs. Exercise training and disease processes can affect these metabolic setpoint values, but the setpoint values are returned to pre-training or pre-disease levels if the training stimulus is removed or if the disease process is cured. Further work is required to determine what the ultimate system regulator of metabolic setpoint values is, why some setpoint values are more stringently protected by homeostatic regulatory mechanisms than others, and the role of conscious decision making processes in determining the regulation of metabolic setpoint values.

Adaptation, Physiological↗
PubMed2005

The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment.

AIM: The purposes of this study were to determine (i) the effects of different facing air velocities on body temperature and heat storage during exercise in hot environmental conditions and (ii) the effects of ingesting fluids at two different rates on thermoregulation during exercise in hot conditions with higher air velocities. METHODS: On five occasions nine subjects cycled for 2 h at 33.0 +/- 0.4 degrees C with a relative humidity of 59 +/- 3%. Air velocity was maintained at 0.2 km h(-1) (0 WS), 9.9 +/- 0.3 km h(-1) (10 WS), 33.3 +/-2.2 km h(-1) (100 WS) and 50.1 +/- 3.2 km h(-1) (150 WS) while subjects replaced 58.8 +/- 6.8% of sweat losses. In the fifth condition, air velocity was maintained at 33.7 +/- 2.2 km h(-1) and subjects replaced 80.0 +/- 6.8% of sweat losses (100.80 WS). RESULTS: Heat storage, body temperature and rating of perceived exertion were higher in 0 and 10 WS compared with all other conditions. There were no differences in any measured variable between 100 and 150 WS, or between 100 and 100.80 WS. Thus, the evaporative capacity of the environment is increased with higher air velocities, reducing heat storage and body temperature. At higher air velocities, a higher rate of fluid ingestion did not influence heat storage, body temperature or sweat rate. CONCLUSION: The finding of previous laboratory studies showing a beneficial effect of high rates of fluid ingestion on thermoregulation during exercise in hot, humid, windstill conditions cannot be extrapolated to out-of-doors exercise in which facing air velocities are seldom lower than the athlete's rate of forward progression.

Adult↗
PubMed2004

Skeletal muscle pathology in endurance athletes with acquired training intolerance.

BACKGROUND: It is well established that prolonged, exhaustive endurance exercise is capable of inducing skeletal muscle damage and temporary impairment of muscle function. Although skeletal muscle has a remarkable capacity for repair and adaptation, this may be limited, ultimately resulting in an accumulation of chronic skeletal muscle pathology. Case studies have alluded to an association between long term, high volume endurance training and racing, acquired training intolerance, and chronic skeletal muscle pathology. OBJECTIVE: To systematically compare the skeletal muscle structural and ultrastructural status of endurance athletes with acquired training intolerance (ATI group) with asymptomatic endurance athletes matched for age and years of endurance training (CON group). METHODS: Histological and electron microscopic analyses were carried out on a biopsy sample of the vastus lateralis from 18 ATI and 17 CON endurance athletes. The presence of structural and ultrastructural disruptions was compared between the two groups of athletes. RESULTS: Significantly more athletes in the ATI group than in the CON group presented with fibre size variation (15 v 6; p = 0.006), internal nuclei (9 v 2; p = 0.03), and z disc streaming (6 v 0; p = 0.02). CONCLUSIONS: There is an association between increased skeletal muscle disruptions and acquired training intolerance in endurance athletes. Further studies are required to determine the nature of this association and the possible mechanisms involved.

Adult↗
PubMed2004

Dissociation between back pain and bone stress reaction as measured by CT scan in young cricket fast bowlers.

BACKGROUND: Bone stress reaction is prevalent among cricket fast bowlers. Few studies have addressed the sensitivity and specificity of imaging for diagnosis, and follow up assessment has been poorly investigated. OBJECTIVE: To determine whether there was an association between back pain and bone stress reaction as measured by computed tomography (CT) scan in young cricket fast bowlers. METHODS: Ten young cricket fast bowlers were included in the study. Nine bowlers presented to a physiotherapy practice with low back pain and were later diagnosed with lumbar stress fractures, while one was an experienced bowler with no pain. All players had a CT scan after presenting to the physiotherapy practice. Pain was assessed according to a subjective scale (0-10) where 10 represented the player's subjective, maximum pain score. Recovery and rehabilitation of all players was monitored until they returned to full participation. RESULTS: There was no consistency in the relationship between pain and CT scan results. For example, one subject had evidence of un-united stress fractures after 15 months of rest but had experienced moderate pain for only 2 weeks after the onset of symptoms, in contrast to another subject who had intermittent pain for 11 months even though CT scan showed multiple stress fractures ranging from partially healed to fully healed status at 3 months. CONCLUSION: There is dissociation between back pain and bone stress reaction as measured by CT scan. Therefore, CT scan does not provide objective evidence for ongoing management or decision concerning return to sport in cricket fast bowlers.

Adolescent↗
PubMed2003

Effects of supramaximal exercise on the electromyographic signal.

AIM: To determine the neuromuscular recruitment characteristics during supramaximal exercise. METHODS: Ten healthy subjects completed the Wingate anaerobic test (WAT) cycling protocol. Electromyographic (EMG) data and rate of fatigue were recorded throughout the cycling. RESULTS: The mean (SD) rate of fatigue (decrease in power output) was 44.5 (8.6)%. No significant change was found in EMG amplitude. A significant decrease (p<0.01) in mean power frequency spectrum was found over the 30 second period. CONCLUSIONS: During WAT, mean power frequency spectrum was attenuated with no decline in EMG amplitude, which may be caused by an accumulation of metabolites in the periphery. However, it is also possible that the feedback loop from intramuscular metabolism to the central nervous system is unable, within the 30 second period of the WAT, to affect neural recruitment strategy.

Adult↗
PubMed2002

The effects of heat stress on neuromuscular activity during endurance exercise.

This study analysed the effect of hot (35 degrees C) and cold (15 degrees C) environments on electromyographic (EMG) signal characteristics, skin and rectal temperatures and heart rate during progressive endurance exercise. Eight healthy subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak sustained power output and then cycled at increasing (15 W/min) work rates to exhaustion in both 35 degrees C and 15 degrees C environments. Skin and rectal temperatures, heart rate and EMG data were measured during the trials. The skin temperatures were higher and the subjects felt more uncomfortable in the hot conditions (Bedford scale) ( P<0.01). Rectal temperature was slightly, but not significantly, higher under hot conditions. Heart rate was significantly higher in the hot group (between condition P<0.05). Peak power output (267.4+/-67.7 W vs. 250.1+/-61.5 W) and time-to-exhaustion (55.7+/-16.7 min vs. 54.5+/-17.1 min) (COLD vs. HOT) were not different between conditions. There were no differences in integrated EMG (IEMG) or mean power frequency spectrum between conditions. Rating of perceived exertion increased similarly in both conditions over time. Although the hot conditions increased heart rate and skin temperature, there were no differences in muscle recruitment or maximal performance, which suggests that the thermal stress of 35 degrees C, in combination with exercise, did not impair maximal performance in this study.

Adult↗
PubMed2001

Influence of ambient temperature on plasma ammonia and lactate accumulation during prolonged submaximal and self-paced running.

This study examined the effects of heat stress on the accumulation of plasma ammonia, lactate, and urate during prolonged running. Nine highly trained endurance runners completed two running trials in a counterbalanced fashion in cool (15 degrees C) and in hot (35 degrees C) humid (60% relative humidity) conditions. Subjects ran on a motorised treadmill at 70% of peak treadmill running speed for 30 min (submaximal) followed by a self-paced 8-km performance run. Blood was drawn at pre-exercise, end-submaximal and end-performance run and analysed for plasma ammonia, lactate, and urate. Four subjects failed to complete the performance run in the heat and the performance times for the rest of the subjects was increased from 27.3 (0.6) min in cool conditions to 31.3 (1.2) min in hot conditions (P < 0.05). The end-performance rectal temperature was 38.6 (0.1) and 39.2 (0.1) degrees C (P<0.05) in cool and hot conditions, respectively. Differences in plasma lactate at the end of submaximal running were not significant. However, at the end of performance runs lactate was 6.0 (0.9) m mol x l(-1) in cool and 3.1 (0.5) mmol x l(-1) in hot conditions, values that were significantly different (P<0.05). Plasma ammonia increased from pre-exercise to approximately equal to 59 micromol x l(-1) at the end-submaximal runs for both coditions and further at the end of performance runs to 108.5 (11) micromol x l(-1) (P<0.05) in hot but not in cool conditions. Plasma urate increased from pre-exercise to 311.2 (25.9) micromol x l(-1) at end-submaximal runs and to approximately equal to 320.4 micromol x l(-1) at end-performance runs in hot and cool environments. The findings that plasma urate accumulation was similar at the completion of running in both conditions, while ammonia was significantly augmented in hot conditions compared with cool, suggest that ammonia accumulation during heat stress exercise might be derived from sources other than purine catabolism.

Adult↗
PubMed2001

Effects of androgen manipulation on postprandial triglyceridaemia, low-density lipoprotein particle size and lipoprotein(a) in men.

Although androgenic hormones decrease HDLC concentration, no direct evidence has linked them to atherosclerosis. The present study was undertaken to extend our ability to assess risk associated with androgen induced lipoprotein(Lp) changes by simultaneously gathering information about postprandial triglyceridaemia (PPT), LDL particle size, HDL and Lp(a) in men either taking exogenous androgens or with suppressed endogenous androgen concentrations. The experimental groups comprised nine male bodybuilders who self-administered anabolic-androgenic steroids (AAS) for a mean period of 6.5 weeks, and 10 healthy men whose testosterone concentration had been reversibly suppressed for 5 weeks using the GnRH agonist triptorelin (Decapeptyl; D-Trp-6-LHRH). A separate group receiving no hormonal treatment provided analytical control (n=7). Lipoprotein size was assessed by gradient gel electrophoresis categorisation (GGE), lipoprotein concentrations by immuno and enzymatic assays and PPT by a standardised oral fat tolerance test (65g /m(2)). Testosterone concentration was significantly reduced on triptorelin from 7.32+/-1.92 to 1.15+/-0.57 ng/ml (P=0.002). High dose AAS use was confirmed by urinalysis. With AAS use, mean HDLC and Lp(a) concentrations and PPT decreased from 0.9+/-0.3 to 0.7+/-0.3 mmol/l (P=0.004), 125+/-128 to 69+/-73 U/l (P=0.008) and 11.6+/-10.0 mmol/l h to 7.5+/-5.4 mmol/l h (P=0.027) respectively. Mean total cholesterol and LDLC were unchanged. LDL size was unchanged in six AAS users, decreased in one but remaining in the normal size range, and increased in two from small LDL to the normal range. Size changes in the latter two subjects were associated with 42 and 58% reductions in PPT respectively. In the triptorelin group, mean total cholesterol, HDLC and Lp(a) were increased from 4.8+/-0.8 mmol/l to 5.2+/-1.0 mmol/l (P=0.039), 1.1+/-0.2 to 1.4+/-0.3 mmol/l (P=0.002) and 278+/-149 to 377+/-222 U/l (P=0.004) respectively. Mean LDLC concentration and PPT were unchanged. LDL particle size increased in four, decreased in two, and was unchanged in four subjects. LDL size decreased in two and showed no change in the other five control subjects. Other lipid measures were unchanged in the control group. Thus, apart from lowering HDLC concentrations, no other potentially atherogenic effects of endogenous androgens or AAS were observed. A suppression of Lp(a) as well as a reduced PPT and increased LDL size in predisposed individuals may be antiatherogenic effects of AAS.

Adult↗
PubMed2001

Reliability of a 5-m multiple shuttle test.

The aim of the present study was to determine the reliability of a modified 5-m multiple shuttle test. The 'match-related fitness' of 23 female hockey players was assessed on four occasions within 4 weeks. The results of each test session and each shuttle were analysed using analysis of variance with repeated measures to determine the reliability of the test. The mean distance for each of the six shuttles decreased (121.2 +/- 7.5, 114.5 +/- 7.5, 112.2 +/- 7.5, 109.9 +/- 7.9, 108.4 +/- 8.1 and 108.7 +/- 8.3 m for shuttles 1-6, respectively; P < 0.001) similarly for each of the four sessions (P = 0.99). The total and peak distances covered during the tests were not significantly different (P = 0.99 and P = 0.12, respectively). The intra-class correlation coefficient (R) for these variables was 0.98 and 0.86, respectively. The delta distance and the fatigue index calculated post-test were significantly different (P = 0.001 and P = 0.006, respectively) between the four sessions. The intra-class correlation coefficient for both these variables was 0.74. Heart rate and rating of perceived exertion (RPE) were not significantly different between sessions (P = 0.42 and P = 0.095, respectively). The intra-class correlation coefficient for heart rate ranged from 0.65 to 0.97 and that for RPE from 0.85 to 0.91. We conclude that the 5-m multiple shuttle run test is a reliable measure of total and peak distances, heart rate and RPE response and is sufficiently reliabile to track changes in fitness over a season. The delta distance and fatigue index are not as reliable and should be interpreted with caution.

Adult↗
PubMed2001

Free living energy expenditure in post menopausal women before and after exercise training.

The aim of the study was to determine the effects of 8 weeks of moderate exercise training, on 24-hour free living energy expenditure in previously sedentary post-menopausal women. The experimental group (EX) included 9 women. Ten non-exercising control subjects (CON) were recruited to undergo pre- and post-testing. Estimated total daily energy expenditure (TDEE), total 24-hour heart beats (HB), total energy intake (TEI), resting metabolic rate, maximal oxygen consumption (VáO2max), body composition, and submaximal heart rate were measured before and after the exercise intervention. Body composition did not change (body fat % in CON 34.0 +/- 4.0% vs. 33.9 +/- 3.6% and EX 34.1 +/- 4.0% vs. 34.0 +/- 3.4%). Mean submaximal heart rate during steady-state exercise in EX was lower after training compared to CON (p < .05); however, VáO2max did not increase significantly (CON 1.96 +/- 0.23 vs. 1.99 +/- 0.24 l L O2/min and EX 1.86 +/- 0.39 vs. 1.94 +/- 0.30 L O2/min). Neither estimated TDEE (CON, 11.6 +/- 2.0 vs. 11.4 +/- 2.78 MJ; and EX 11.4 +/- 3.3 vs. 11.5 +/- 2.5 MJ, pre vs. post, respectively), RMR (CON 134.2 +/- 9.4 vs. 136.9 +/- 15.0 KJ/kgFFM/day, and EX 138.4 +/- 6.4 vs. 140.7 +/- 14.2 KJ/kgFFM/day, pre vs. post, respectively), TEI (CON 7.9 +/- 2.2 vs. 8.2 +/- 2.5 MJ, and EX 9.4 +/-1.6 vs. 8.3 +/- 2.8 MJ), nor HB (CON 110,808 +/- 12,574 vs. 107,366 +/- 12,864 beats, and EX 110,188 +/- 9,219 vs. 114,590 +/- 12,750 beats) change over 8 weeks in either group. These data suggest that a moderate exercise program may not impact on TDEE, RMR, TEI, or HB in previously sedentary, older women.

Basal Metabolism↗
PubMed2001

The influence of sensory cues on the perception of exertion during exercise and central regulation of exercise performance.

The perception of effort during exercise and its relationship to fatigue is still not well understood. Although several scales have been developed to quantify exertion Borg's 15-point ratings of perceived exertion (RPE) scale has been adopted as a valid and reliable instrument for evaluating whole body exertion during exercise. However, Borg's category-ratio scale is useful in quantifying sensations of exertion related to those variables that rise exponentially with increases in exercise intensity. Previous research has examined the extent to which afferent feedback arising from cardiopulmonary and peripheral variables mediates the perception of exertion. However, the literature has not identified a single variable that consistently explains exertion ratings. It is concluded that effort perception involves the integration of multiple afferent signals from a variety of perceptual cues. In a process defined as teleoanticipation, the changes in perceived exertion that result from these afferent signals may allow exercise performance to be precisely regulated such that a task can be completed within the biomechanical and metabolic limits of the body. The accuracy with which individuals can regulate exercise intensity based upon RPE values, the decrease in muscle recruitment (central drive) that occurs before fatigue, and the extent to which perceived exertion and heart rate can be altered with hypnosis and biofeedback training all provide evidence for the existence of such a regulatory system. Future research is needed to precisely quantify the extent to which efferent feedforward commands and afferent feedback determine pacing strategies such that an exercise event can be completed without irreversible tissue damage.

Biomechanical Phenomena↗
PubMed2001

Peak rates of diuresis in healthy humans during oral fluid overload.

OBJECTIVE: To determine whether rates of intestinal fluid absorption and renal diuresis can match high rates of fluid ingestion in healthy humans exposed to oral fluid overload, thereby preventing the development of hyponatraemia either by reverse sodium movement across the intestine (the Priestley-Haldane effect) or by expansion of the extracellular fluid volume. METHODS: Changes in renal function and in plasma chemical measurements in response to an oral fluid overload (0.9-1.8 l/h x 3 h) were investigated in 6 healthy control subjects at rest, and in a subject with a history of exercise-induced symptomatic hyponatraemia, during both prolonged (160-minute) exercise and at rest. FINDINGS: All control subjects gained weight (2.7 +/- 0.2 kg, mean +/- standard error of mean (SEM)) because the rate of oral fluid intake exceeded the peak rate of urine production (778 +/- 39 ml/h). Blood volume rose by 7.1 (+/- 0.5)% and plasma sodium concentrations fell progressively from 144 +/- 2.6 to 136 +/- 1.1 mmol/l (P < 0.05) in the control subjects. Plasma potassium and angiotensin II concentrations were unchanged and creatinine clearance was normal (approximately 125 ml/min). Free water clearance reached a maximum of 11.2 +/- 0.9 ml/min after 2 hours. The increase in body mass could be accounted for by calculated or measured changes in extra- and intracellular fluid volumes. Similar changes were measured in the subject with a previous history of symptomatic hyponatraemia. CONCLUSION: The rate of intestinal fluid absorption appeared to match the rate of oral fluid ingestion and there was no evidence of fluid accumulation in the intestine with reverse sodium movement from the extracellular space into intestinal fluid. The results of this study are therefore at variance with the Priestley-Haldane hypothesis and suggest that reverse sodium movement did not contribute to the hyponatraemia induced by oral fluid overload in these subjects. Rather it appears that humans may have a limited capacity to excrete fluid at rates in excess of approximately 900 ml/h in response to higher rates of oral fluid intake. When the rate of intestinal fluid absorption matches the rate of fluid ingestion and exceeds the kidneys' maximum capacity for fluid excretion, the excess fluid accumulates in the extra- and intracellular fluid compartments, inducing the dilutional hyponatraemia of water intoxication. These findings may have relevance to other clinical conditions in which hyponatraemia develops in response to high rates of oral or intravenous fluid provision.

Adult↗
PubMed2000

Advantages of smaller body mass during distance running in warm, humid environments.

The purpose of this study was to examine the extent to which lighter runners might be more advantaged than larger, heavier runners during prolonged running in warm humid conditions. Sixteen highly trained runners with a range of body masses (55-90 kg) ran on a motorised treadmill on three separate occasions at 15, 25 or 35 degrees C, 60% relative humidity and 15 km x h(-1) wind speed. The protocol consisted of a 30-min run at 70% peak treadmill running speed (sub-max) followed by a self-paced 8-km performance run. At the end of the submax and 8-km run, rectal temperature was higher at 35 degrees C (39.5+/-0.4 degrees C, P<0.05) compared with 15 degrees C (38.6+/-0.4 degrees C) and 25 degrees C (39.1+/-0.4 degrees C) conditions. Time to complete the 8-km run at 35 degrees C was 30.4+/-2.9 min (P<0.05) compared with 27.0+/-1.5 min at 15 degrees C and 27.4+/-1.5 min at 25 degrees C. Heat storage determined from rectal and mean skin temperatures was positively correlated with body mass (r=0.74, P<0.0008) at 35 degrees C but only moderately correlated at 25 degrees C (r=0.50, P<0.04), whereas no correlation was evident at 15 degrees C. Potential evaporation estimated from sweat rates was positively associated with body mass (r=0.71, P<0.002) at 35 degrees C. In addition, the decreased rate of heat production and mean running speed during the 8-km performance run were significantly correlated with body mass (r=-0.61, P<0.02 and r=-0.77, P<0.0004, respectively). It is concluded that, compared to heavier runners, those with a lower body mass have a distinct thermal advantage when running in conditions in which heat-dissipation mechanisms are at their limit. Lighter runners produce and store less heat at the same running speed; hence they can run faster or further before reaching a limiting rectal temperature.

Blood Volume↗
PubMed2000

Different neuromuscular recruitment patterns during eccentric, concentric and isometric contractions.

Aim. The purpose of this study was to determine the neuromuscular fatigue profiles during 100 s isometric (ISO), concentric (CON), and eccentric (ECC) activity.Methods. Twelve subjects (age 25.1+/-3.7 years, mass 70.1+/-8.2 kg, mean+/-SD) performed ISO, CON and ECC maximal voluntary contractions and 100 s endurance trials on an isokinetic dynamometer. Raw EMG data were recorded throughout each trial from the rectus femoris of the right limb. Corresponding data for integrated electromyography (IEMG), percentile frequency shifts (MPFS) and peak torque output were divided into five 5 s epochs and subsequently normalised with the first epoch being the reference point, in order to assess changes over time.Results. There were no significant differences between ECC, CON and ISO peak torque output (211+/-63 vs 169+/-41 vs 177+/-61 Nm; ECC, CON, ISO) and IEMG activity (280+/-143 vs 305+/-146 vs 287+/-143 mV; ECC, CON, ISO) during maximal contractions. Serial reductions in torque output were greatest in ISO in which torque output during the final epoch was 31+/-13% of initial values, similar to the final torque values in CON (58+/-15%), but significantly less than ECC (108.6+/-38.6%; P<0. 001) values. In CON and ECC, IEMG was maintained (95+/-27% and 93+/-21%; CON and ECC), whereas IEMG for ISO decreased to 38+/-13% of initial values. The greatest reduction in MPFS occurred in CON (69+/-10%) compared to ISO (78+/-9%; P<0.05) and ECC (93+/-6%; P<0.001).Conclusion. These data demonstrate distinct neuromuscular fatigue profiles for the different types of muscle contraction. Whereas eccentric activity was largely fatigue resistant, isometric and concentric contractions displayed different neuromuscular fatigue profiles.

Adult↗