Christopher J. Gore

Effects of exercise intensity and duration on the excess post-exercise oxygen consumption

Abstract Recovery from a bout of exercise is associated with an elevation in metabolism referred to as the excess post-exercise oxygen consumption (EPOC). A number of investigators in the first half of the last century reported prolonged EPOC durations and that the EPOC was a major component of the thermic effect of activity. It was therefore thought that the EPOC was a major contributor to total daily energy expenditure and hence the maintenance of body mass. Investigations conducted over the last two or three decades have improved the experimental protocols used in the pioneering studies and therefore have more accurately characterized the EPOC. Evidence has accumulated to suggest an exponential relationship between exercise intensity and the magnitude of the EPOC for specific exercise durations. Furthermore, work at exercise intensities ≥50 – 60% [Vdot]O2max stimulate a linear increase in EPOC as exercise duration increases. The existence of these relationships with resistance exercise at this stage remains unclear because of the limited number of studies and problems with quantification of work intensity for this type of exercise. Although the more recent studies do not support the extended EPOC durations reported by some of the pioneering investigators, it is now apparent that a prolonged EPOC (3 – 24 h) may result from an appropriate exercise stimulus (submaximal: ≥50 min at ≥70% [Vdot]O2max; supramaximal: ≥6 min at ≥105% [Vdot]O2max). However, even those studies incorporating exercise stimuli resulting in prolonged EPOC durations have identified that the EPOC comprises only 6 – 15% of the net total oxygen cost of the exercise. But this figure may need to be increased when studies utilizing intermittent work bouts are designed to allow the determination of rest interval EPOCs, which should logically contribute to the EPOC determined following the cessation of the last work bout. Notwithstanding the aforementioned, the earlier research optimism regarding an important role for the EPOC in weight loss is generally unfounded. This is further reinforced by acknowledging that the exercise stimuli required to promote a prolonged EPOC are unlikely to be tolerated by non-athletic individuals. The role of exercise in the maintenance of body mass is therefore predominantly mediated via the cumulative effect of the energy expenditure during the actual exercise.

''Live high, train low'' does not change the total haemoglobin mass of male endurance athletes sleeping at a simulated altitude of 3000 m for 23 nights

Abstract The purpose of this study was to document the effect of 23 days of “live high, train low” on the haemoglobin mass of endurance athletes. Thirteen male subjects from either cycling, triathlon or cross-country skiing backgrounds participated in the study. Six subjects (HIGH) spent 8−10 h per night in a “nitrogen house” at a simulated altitude of 3000 m in normobaric hypoxia, whilst control subjects slept at near sea level (CONTROL, n = 7). Athletes logged their daily training sessions, which were conducted at 600 m. Total haemoglobin mass (as measured using the CO-rebreathing technique) did not change when measured before (D1 or D2) and after (D28) 23 nights of hypoxic exposure [HIGH 990 (127) vs 972 (97) g and CONTROL 1042 (133) vs 1033 (138) g, before and after simulated altitude exposure, respectively]. Nor was there any difference in the substantial array of reticulocyte parameters measured using automated flow cytometry prior to commencing the study (D1), after 6 (D10) and 15 (D19) nights of simulated altitude, or 1 day after leaving the nitrogen house (D28) when HIGH and CONTROL groups were compared. We conclude that red blood cell production is not stimulated in male endurance athletes who spend 23 nights at a simulated altitude of 3000 m.

Associations of physical activity with body weight and fat in men and women

OBJECTIVE: Increasing physical activity is strongly advocated as a key public health strategy for weight gain prevention. We investigated associations of leisure-time physical activity (LTPA) and occupational/domestic physical activity with body mass index (BMI) and a skinfold-derived index of body fat (sum of six skinfolds), among normal-weight and overweight men and women.DESIGN: Analyses of cross-sectional self-report and measured anthropometric data.SUBJECTS: A total of 1302 men and women, aged 18–78 y, who were part of a randomly selected sample and who agreed to participate in a physical health assessment.MEASUREMENTS: Self-report measures of physical activity, measured height and weight, and a skinfold-derived index of body fatness.RESULTS: Higher levels of LTPA were positively associated with the likelihood of being in the normal BMI and lower body fat range for women, but few or no associations were found for men. No associations were found between measures of occupational/domestic activity and BMI or body fat for men or women.CONCLUSION: By using a skinfold sum as a more direct measure of adiposity, this study extends and confirms the previous research that has shown an association between BMI and LTPA. Our results suggest gender differences in the relationship of leisure-time physical activity with body fatness. These findings, in conjunction with a better understanding of the causes of such differences, will have important public health implications for the development and targeting of weight gain prevention strategies.

Effects of Acute Alkalosis and Acidosis on Performance

Ingestion of agents that modify blood buffering action may affect high-intensity performance. Here we present a meta-analysis of the effects of acute ingestion of three such agents — sodium bicarbonate, sodium citrate and ammonium chloride — on performance and related physiological variables (blood bicarbonate, pH and lactate). A literature search yielded 59 useable studies with 188 observations of performance effects. To perform the mixed-model meta-analysis, all performance effects were converted into a percentage change in mean power and were weighted using standard errors derived from exact p-values, confidence limits (CLs) or estimated errors of measurement. The fixed effects in the meta-analytic model included the number of performance-test bouts (linear), test duration (log linear), blinding (yes/no), competitive status (athlete/nonathlete) and sex (male/female). Dose expressed as buffering mmoL/kg/body mass (BM) was included as a strictly proportional linear effect interacted with all effects except blinding. Probabilistic inferences were derived with reference to thresholds for small and moderate effects on performance of 0.5% and 1.5%, respectively. Publication bias was reduced by excluding study estimates with a standard error >2.7%. The remaining 38 studies and 137 estimates for sodium bicarbonate produced a possibly moderate performance enhancement of 1.7% (90% CL± 2.0%) with a typical dose of 3.5mmoL/kg/BM (~0.3 g/kg/BM) in a single 1-minute sprint, following blinded consumption by male athletes. In the 16 studies and 45 estimates for sodium citrate, a typical dose of 1.5mmoL/kg/BM (~0.5 g/kg/BM) had an unclear effect on performance of 0.0% (±1.3%), while the five studies and six estimates for ammonium chloride produced a possibly moderate impairment of 1.6% (±1.9%) with a typical dose of 5.5mmoL/kg/BM (~0.3 g/kg/BM). Study and subject characteristics had the following modifying small effects on the enhancement of performance with sodium bicarbonate: an increase of 0.5% (±0.6%) with a 1mmoL/kg/BM increase in dose; an increase of 0.6% (±0.4%) with five extra sprint bouts; a reduction of 0.6% (±0.9%) for each 10-fold increase in test duration (e.g. 1–10 minutes); reductions of 1.1%(±1.1%) with nonathletes and 0.7% (±1.4%) with females. Unexplained variation in effects between research settings was typically ±1.2%. The only noteworthy effects involving physiological variables were a small correlation between performance and pre-exercise increase in blood bicarbonate with sodium bicarbonate ingestion, and a very large correlation between the increase in blood bicarbonate and time between sodium citrate ingestion and exercise. The approximate equal and opposite effects of sodium bicarbonate and ammonium chloride are consistent with direct performance effects of pH, but sodium citrate appears to have some additional metabolic inhibitory effect. Important future research includes studies of sodium citrate ingestion several hours before exercise and quantification of gastrointestinal symptoms with sodium bicarbonate and citrate. Although individual responses may vary, we recommend ingestion of 0.3–0.5 g/kg/BM sodium bicarbonate to improve mean power by 1.7% (±2.0%) in high-intensity races of short duration.

Simulated moderate altitude elevates serum erythropoietin but does not increase reticulocyte production in well-trained runners

Abstract The purpose of this study was to investigate whether the modest increases in serum erythropoietin (sEpo) experienced after brief sojourns at simulated altitude are sufficient to stimulate reticulocyte production. Six well-trained middle-distance runners (HIGH, mean maximum oxygen uptake, V˙O2max = 70.2 ml · kg−1 · min−1) spent 8–11 h per night for 5 nights in a nitrogen house that simulated an altitude of 2650 m. Five squad members (CONTROL, mean V˙O2max = 68.9 ml · kg−1 · min−1) undertook the same training, which was conducted under near-sea-level conditions (600 m altitude), and slept in dormitory-style accommodation also at 600 m altitude. For both groups, this 5-night protocol was undertaken on three occasions, with a 3-night interim between successive exposures. Venous blood samples were measured for sEpo after 1 and 5 nights of hypoxia on each occasion. The percentage of reticulocytes was measured, along with a range of reticulocyte parameters that are sensitive to changes in erythropoiesis. Mean serum erythropoietin levels increased significantly (P < 0.01) above baseline values [mean (SD) 7.9 (2.4) mU · ml−1] in the HIGH group after the 1st night [11.8 (1.9) mU · ml−1, 57%], and were also higher on the 5th night [10.7 (2.2) mU · ml−1, 42%] compared with the CONTROL group, whose erythropoietin levels did not change. After athletes spent 3 nights at near sea level, the change in sEpo during subsequent hypoxic exposures was markedly attenuated (13% and −4% change during the second exposure; 26% and 14% change during the third exposure; 1st and 5th nights of each block, respectively). The increase in sEpo was insufficient to stimulate reticulocyte production at any time point. We conclude that when daily training loads are controlled, the modest increases in sEpo known to occur following brief exposure to a simulated altitude of 2650 m are insufficient to stimulate reticulocyte production.

The effect of altitude on cycling performance: a challenge to traditional concepts.

Acute exposure to moderate altitude is likely to enhance cycling performance on flat terrain because the benefit of reduced aerodynamic drag outweighs the decrease in maximum aerobic power [maximal oxygen uptake (V̇O2max)]. In contrast, when the course is mountainous, cycling performance will be reduced at moderate altitude.Living and training at altitude, or living in an hypoxic environment (~2500m) but training near sea level, are popular practices among elite cyclists seeking enhanced performance at sea level. In an attempt to confirm or refute the efficacy of these practices, we reviewed studies conducted on highly-trained athletes and, where possible, on elite cyclists. To ensure relevance of the information to the conditions likely to be encountered by cyclists, we concentrated our literature survey on studies that have used 2- to 4-week exposures to moderate altitude (1500 to 3000m). With acclimatisation there is strong evidence of decreased production or increased clearance of lactate in the muscle, moderate evidence of enhanced muscle buffering capacity (βm) and tenuous evidence of improved mechanical efficiency (ME) of cycling.Our analysis of the relevant literature indicates that, in contrast to the existing paradigm, adaptation to natural or simulated moderate altitude does not stimulate red cell production sufficiently to increase red cell volume (RCV) and haemoglobin mass (Hbmass). Hypoxia does increase serum erthyropoietin levels but the next step in the erythropoietic cascade is not clearly established; there is only weak evidence of an increase in young red blood cells (reticulocytes).Moreover, the collective evidence from studies of highly-trained athletes indicates that adaptation to hypoxia is unlikely to enhance sea level V̇O2max. Such enhancement would be expected if RCV and Hbmass were elevated.The accumulated results of 5 different research groups that have used controlled study designs indicate that continuous living and training at moderate altitude does not improve sea level performance of high level athletes. However, recent studies from 3 independent laboratories have consistently shown small improvements after living in hypoxia and training near sea level. While other research groups have attributed the improved performance to increased RCV and V̇O2max, we cite evidence that changes at the muscle level (βm and ME) could be the fundamental mechanism. While living at altitude but training near sea level may be optimal for enhancing the performance of competitive cyclists, much further research is required to confirm its benefit. If this benefit does exist, it probably varies between individuals and averages little more than 1%.

The relationship between body mass index and waist circumference: implications for estimates of the population prevalence of overweight.

OBJECTIVE: Body mass index (BMI) based on self‐reported height and weight is a systematically biased, but acceptable measure of adiposity and is commonly used in population surveys. Recent studies indicate that abdominal obesity is more strongly associated with obesity‐related health problems than is adiposity measured by BMI. The purpose of this study was to determine the relationships of both measured and self‐reported BMI with measured waist circumference in a randomly selected sample of Australian adults.DESIGN: Cross‐sectional survey with self‐reported and laboratory‐based measures of adiposity.SUBJECTS: 1140 randomly‐selected Australian adults aged 18–78 y resident in the city of Adelaide, South Australia.MEASUREMENTS: Data on self‐reported and measured height and weight as well as measured waist circumference were drawn from the Pilot Survey of the Fitness of Australians database. The proportion of men and women with acceptable BMI (BMI≤25 kg/m2) and with excess abdominal adiposity (≥94 cm for men and ≥80 cm for women) was determined. Differences in the prevalence of overweight based on BMI alone or BMI and waist circumference were also determined.RESULTS: Compared with the prevalence based on self‐reported BMI alone, the prevalence of overweight among men based on self‐reported BMI and waist circumference combined was 2.4%, 5.3%, 19.1% and 7.5% greater for men aged 18–39 y, 40–59 y, 60–78 y and for all men, respectively. Among women, compared with the prevalence based on self‐reported BMI alone, the prevalence of overweight based on the combined measures was 9.9%, 24.0%, 33.3% and 20.6% greater for women aged 18–39 y, 40–59 y, 60–78 y and for all women, respectively.CONCLUSIONS: If waist circumference is used as the criterion, then the prevalence of overweight among Australian adults, and probably other Caucasian populations, may be significantly greater than indicated by surveys relying on self‐reported height and weight. The development of valid self‐reported measures of waist circumference for use in population surveys may allow more accurate epidemiological monitoring of overweight and obesity.

Effects of a 12-day live high, train low camp on reticulocyte production and haemoglobin mass in elite female road cyclists

Abstract The aim of this study was to document the effect of “living high, training low” on the red blood cell production of elite female cyclists. Six members of the Australian National Womens road cycling squad slept for 12 nights at a simulated altitude of 2650 m in normobaric hypoxia (HIGH), while 6 team-mates slept at an altitude of 600 m (CONTROL). HIGH and CONTROL subjects trained and raced as a group throughout the 70-day study. Baseline levels of reticulocyte parameters sensitive to changes in erythropoeisis were measured 21 days and 1 day prior to sleeping in hypoxia (D1 and D20, respectively). These measures were repeated after 7 nights (D27) and 12 nights (D34) of simulated altitude exposure, and again 15 days (D48) and 33 days (D67) after leaving the altitude house. There was no increase in reticulocyte production, nor any change in reticulocyte parameters in either the HIGH or CONTROL groups. This lack of haematological response was substantiated by total haemoglobin mass measures (CO-rebreathing), which did not change when measured on D1, D20, D34 or D67. We conclude that in elite female road cyclists, 12 nights of exposure to normobaric hypoxia (2650 m) is not sufficient to either stimulate reticulocyte production or increase haemoglobin mass.

Reduced performance of male and female athletes at 580 m altitude

Abstract This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O2peak) and performance of ten trained male athletes [ (SEM); O2peak = 72.4 (2.2) ml · kg−1 · min−1] and ten trained female athletes [O2peak = 60.8 (2.1) ml · kg−1 · min−1]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33 kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ) at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (SaO2) at O2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus 92.1 (3.0)%]. While SaO2 at O2peak was not different between men and women, it was concluded that relative, rather than absolute, O2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the decrease in O2peak could be accounted for by a decrease in O2 delivery, which indicates that reduced O2 tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min.

Relationship between a 14-Day Recall Measure of Leisure-Time Physical Activity and a Submaximal Test of Physical Work Capacity in a Population Sample of Australian Adults

This paper reports on the validity of a 14-day recall measure of leisure time physical activity (LTPA) in a sample of Australian adults (N = 986). Submaximal cycle ergometry was used to assess physical work capacity per kilogram of body mass (pwc75/kg). The self-report energy expenditure estimates were used to categorize respondents as vigorously active, moderately active, and low active/sedentary. Multiple regression analyses showed that pwc75/kg increased significantly across energy expenditure categories for adults aged less than 40 years; that the vigorous and moderate activity categories had greater mean pwc75/kg values than the low/sedentary category for 40 to 59-year-olds; and, that there were no differences in pwc75/kg between activity categories for those aged 60 years or older.