David A. Tanner

Clothing fabric does not affect thermoregulation during exercise in moderate heat.

PURPOSE We investigated whether temperature regulation is improved during exercise in moderate heat by the use of clothing constructed from fabric that was purported to promote sweat evaporation compared with traditional fabrics. METHODS Eight well-trained, euhydrated males performed three exercise bouts wearing garments made from an evaporative polyester fabric (SYN), wearing garments made from traditional cotton fabric (COT), or dressed seminude (S-N) in random order. Bouts consisted of 15 min seated rest, 30 min running at 70% .VO(2max), 15 min walking at 40% .VO(2max), and 15 min seated rest, all at 30 +/- 1 degrees C and 35 +/- 5% relative humidity. COT and SYN clothing ensembles consisted of crew neck, short sleeve T-shirts, cycling shorts, and anklet socks made from their respective materials, and running shoes. The S-N condition consisted of a Lycra swim suit, polyester socks, and running shoes. RESULTS Mean skin temperature was lower for S-N during preexercise rest when compared with SYN and COT. No differences in mean body temperature, rectal temperature, or mean skin temperature were observed during or after exercise. No differences in VO2 or heart rate were observed. No differences in comfort sensations were observed. CONCLUSION In summary, before, during, or after exercise in a moderately warm environmental condition, neither the addition of a modest amount of clothing nor the fabric characteristics of this clothing alters physiological, thermoregulatory, or comfort sensation responses.

Ground contact time as an indicator of metabolic cost in elite distance runners.

UNLABELLED Differences in running economy at common speeds have been demonstrated between male and female distance runners, as well as between middle-distance (MD) and long-distance (LD) specialists. Whether measures of foot ground contact time (tc), known to be proportional to the mass-specific cost of locomotion, follows the same running economy relationships in these groups is unknown. PURPOSE This study examined if differences in tc and selected gait kinematic variables exist between elite male and female distance runners, as well as between elite MD and LD specialists, as running speed increases. METHODS Twelve male and six female elite distance runners completed multiple 30-s trials on a treadmill at common competitive racing velocities. Wireless triaxial 10-g accelerometers, sampling at 1024 Hz, were securely attached to the laces of each shoe. Values of tc, swing time, stride length, and stride frequency were determined from accelerometric output corresponding to foot strike and toe-off events obtained from a minimum of 20 consecutive steps of each foot. A proportional estimate of metabolic cost was obtained by using 1/tc. RESULTS Women displayed shorter tc, swing time, and stride length with greater stride frequency compared with men at common speeds; however, these differences were largely negated by normalizing to standing height. At common speeds, women demonstrated smaller measures of tc compared with men, suggesting an increased metabolic cost, paralleling published oxygen uptake data. MD specialists displayed smaller increases in 1/tc as speed increased, compared with LD specialists. CONCLUSIONS Elite distance runners demonstrate ground contact measures that suggest that known differences in running economy between sexes and event specialties may be a result of differences in running gait.

Expiratory flow limitation confounds ventilatory response during exercise in athletes

INTRODUCTION A significant number of highly trained endurance runners have been observed to display an inadequate hyperventilatory response to intense exercise. Two potential mechanisms include low ventilatory responsiveness to hypoxia and ventilatory limitation as a result of maximum expiratory flow rates being achieved. PURPOSE To test the hypothesis that expiratory flow limitation can complicate determination of ventilatory responsiveness during exercise the following study was performed. METHODS/MATERIALS Sixteen elite male runners were categorized based on expiratory flow limitation observed in flow volume loops collected during the final minute of progressive exercise to exhaustion. Eight flow limited (FL) (VO2max, 75.9+/-2.4 mL x kg(-1) x min(-1); expiratory flow limitation, 47.3+/-20.4%) and eight non-flow limited subjects (NFL) (VO2max, 75.6+/-4.8 mL x kg(-1) x min(-1); expiratory flow limitation, 0.3+/-0.8%) were tested for hypoxic ventilatory responsiveness (HVR). RESULTS Independent groups ANOVA revealed no significant differences between FL and NFL for VO2max, VE max (136.2+/-16.0 vs 137.5+/-21.6 L x min(-1)), VE/VO2, (28.4+/-3.2 vs 27.6+/-2.9 L x lO2(-1)), VE/VCO2 (24.8+/-3.1 vs 24.4+/-2.0 L x lCO2(-1)), HVR (0.2+/-0.2 vs 0.3+/-0.1 L x %SaO2(-1)), or SaO2 at max (89.1+/-2.4 vs 86.6+/-4.1%). A significant relationship was observed between HVR and SaO2 (r = 0.92, P < or = 0.001) in NFL that was not present in FL. Conversely, a significant relationship between VE/VO2 and SaO2 (r = 0.79, P < or = 0.019) was observed in FL but not NFL. Regression analysis indicated that the HVR-SaO2 and SaO2-VE/VO2 relationships differed between groups. DISCUSSION When flow limitation is controlled for, HVR plays a more significant role in determining SaO2 in highly trained athletes than has been previously suggested.

Impairment of 3000-m Run Time at Altitude Is Influenced by Arterial Oxyhemoglobin Saturation

UNLABELLED The decline in maximal oxygen uptake (ΔVO(2)max) with acute exposure to moderate altitude is dependent on the ability to maintain arterial oxyhemoglobin saturation (SaO2). PURPOSE This study examined if factors related to ΔVO(2)max at altitude are also related to the decline in race performance of elite athletes at altitude. METHODS Twenty-seven elite distance runners (18 men and 9 women, VO(2)max = 71.8 ± 7.2 mL·kg(-1)·min(-1)) performed a treadmill exercise at a constant speed that simulated their 3000-m race pace, both in normoxia and in 16.3% O2 (∼2100 m). Separate 3000-m time trials were completed at sea level (18 h before altitude exposure) and at 2100 m (48 h after arrival at altitude). Statistical significance was set at P ≤ 0.05. RESULTS Group 3000-m performance was significantly slower at altitude versus sea level (48.5 ± 12.7 s), and the declines were significant in men (48.4 ± 14.6 s) and women (48.6 ± 8.9 s). Athletes grouped by low SaO2 during race pace in normoxia (SaO2 < 91%, n = 7) had a significantly larger ΔVO(2) in hypoxia (-9.2 ± 2.1 mL·kg(-1)·min(-1)) and Δ3000-m time at altitude (54.0 ± 13.7 s) compared with athletes with high SaO2 in normoxia (SaO2 > 93%, n = 7, ΔVO(2) = -3.5 ± 2.0 mL·kg(-1)·min(-1), Δ3000-m time = 38.9 ± 9.7 s). For all athletes, SaO2 during normoxic race pace running was significantly correlated with both ΔVO(2) (r = -0.68) and Δ3000-m time (r = -0.38). CONCLUSIONS These results indicate that the degree of arterial oxyhemoglobin desaturation, already known to influence ΔVO(2)max at altitude, also contributes to the magnitude of decline in race performance at altitude.

Partitioned weight loss and body composition changes during a mountaineering expedition: a field study

Weight loss and changes in body composition are recognized phenomena associated with high-altitude mountaineering expeditions. Attempts to partition the weight loss between fat mass (FM) and fat-free mass (FFM) have been inconclusive. Therefore, five male subjects, average age 40.0 +/- 5.5 years, were studied prior to, during, and following a 21-day expedition between 2200 m and 4300 m on Mt. McKinley, Alaska. Pre- to postexpedition body composition changes were determined by densitometry, skinfold thickness (12 sites), body girth measurements (14 sites), and cross-sectional area from magnetic resonance imaging (MRI) (three sites). Data analysis by Students t-test (p < 0.05(1) tail) indicated decreases in body weight (4.2 +/- 2.8 kg, 220 g/day, 5.4% of initial weight), total skinfold thickness (10.8%), total body girth (2.8%), and percentage of fat by densitometry (15%). Total cross-sectional area of the three MRI slices (upper arm + thigh + calf) decreased 4.7%, muscle area decreased 9.1%, and fat area decreased 3.9%. The three methods used to partition the weight loss between FM and FFM did not agree: 77% FM vs 23% FFM by densitometry, 25% FM vs 75% FFM by skinfolds, and 38% FM vs 62% FFM by MRI. Energy intake (3640 +/- 1250 kcal/day) was negatively correlated (Pearson r > 0.88(2) tail) with losses in weight (r = -0.89), skinfolds (r = -0.93), and girths (r = -0.88), ie the greater the intake the less the decline. Therefore, insufficient energy intake appeared primarily responsible for the weight loss and changes in body composition during the expedition.

Ventilatory patterns differ between maximal running and cycling

To determine the effect of exercise mode on ventilatory patterns, 22 trained men performed two maximal graded exercise tests; one running on a treadmill and one cycling on an ergometer. Tidal flow-volume (FV) loops were recorded during each minute of exercise with maximal loops measured pre and post exercise. Running resulted in a greater VO2peak than cycling (62.7±7.6 vs. 58.1±7.2mLkg(-1)min(-1)). Although maximal ventilation (VE) did not differ between modes, ventilatory equivalents for O2 and CO2 were significantly larger during maximal cycling. Arterial oxygen saturation (estimated via ear oximeter) was also greater during maximal cycling, as were end-expiratory (EELV; 3.40±0.54 vs. 3.21±0.55L) and end-inspiratory lung volumes, (EILV; 6.24±0.88 vs. 5.90±0.74L). Based on these results we conclude that ventilatory patterns differ as a function of exercise mode and these observed differences are likely due to the differences in posture adopted during exercise in these modes.

Prevalence of Exercise-Induced Arterial Hypoxemia in Distance Runners at Sea Level.

Purpose It has been reported that ~50% of endurance-trained men demonstrate exercise-induced arterial hypoxemia (EIAH) during heavy exercise. However, this often-cited prevalence rate comes from a single study using a cohort of 25 highly trained men who completed maximal cycle ergometry. As arterial oxyhemoglobin saturation (SpO2) during maximal exercise is reported to be significantly lower during treadmill versus cycle ergometry in the same subjects, we hypothesized that the prevalence of EIAH would be greater than previously reported (and commonly referenced) in a larger cohort of highly endurance-trained men during maximal treadmill running. Methods Data from 124 highly trained male distance runners (V˙O2max range = 60.3–84.7 mL·kg−1·min−1) were retrospectively examined from previously published studies completed in the Indiana University Human Performance Laboratory. Subjects completed a constant speed, progressive-grade treadmill exercise test to volitional exhaustion, and arterial oxyhemoglobin saturation (SaO2ear) in all subjects was estimated using the same oximeter (Hewlett Packard 47201A). Results Using similar inclusion criteria as previously published for highly trained (V˙O2max > 68 mL·kg−1·min−1) and for EIAH (SaO2ear ⩽ 91%), 55 of 79 subjects (70%) exhibited exercise-induced arterial desaturation. Across all 124 subjects, 104 (84%) demonstrated at least moderate EIAH (SaO2ear ⩽ 93%) during maximal treadmill exercise. SaO2ear was significantly yet weakly correlated with V˙E/V˙O2 (P < 0.01, r = 0.28) and V˙E/V˙CO2 (P < 0.001, r = 0.33) but not with V˙O2max. Conclusion These results indicate that the prevalence of EIAH in highly trained men during maximal treadmill exercise at sea level is greater compared with previously suggested data, with exercise mode perhaps playing a factor in the number of athletes who experience EIAH.