Joel M. Stager

Energy balance in highly trained female endurance runners

Anecdotal and scientific reports have suggested that some female endurance athletes may have an inexplicable imbalance between energy intake and energy expenditure. We compared energy intake (EI) from food diaries (FD) with assessment of free-living energy expenditure (EE) using doubly labeled water (DLW) and a food attitude survey for 7 d in nine female distance runners. Daily EE via DLW (2990 +/- 415 kcal) was greater (P < 0.01) than daily EI via FD (2037 +/- 298 kcal): a 32% imbalance. Body weight did not change during the 7 d (day 1, 55.3 +/- 6.2 kg; day 7, 55.1 +/- 5.6 kg). A positive relationship was observed between EE and body weight (r = 0.82) while a negative correlation existed between EE vs EI (r = -0.83) and between EI vs body weight (r = -0.74). A negative correlation was observed between body weight and food attitude/body image (r = -78), i.e., the heavier women self-reported lower EI and also reported lower body image scores. These female athletes had a significant imbalance between EI and EE by our measures. Since body image and EI were related to body weight, the estimates of EI may be low due to underreporting particularly by the heavier athletes.

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.

Mood, neuromuscular function, and performance during training in female swimmers.

The effect of seasonal changes in training load on mood, neuromuscular function, and measures of physical power were examined in 12 collegiate women swimmers. These subjects were studied at three training stages during a competitive swim season: baseline (5,000 m.d-1), peak training (8,300 m.d-1), and taper (2,300 m.d-1). Mood was evaluated with the Profile of Mood States. Neuromuscular function was measured via the soleus Hoffmann-reflex (H-reflex). Anaerobic swimming power was assessed with a 30-s tethered swim test, and maximal aerobic power was determined following a maximal 378-m swim. Repeated measures ANOVA revealed that at peak training H-reflex and peak anaerobic swimming power were reduced (P < 0.05) below baseline values by 8.6% and 9.4%, respectively, and total mood disturbance was elevated above baseline (P < 0.01). These variables returned to baseline values at the taper assessment. H-reflex values were correlated with peak (r = 0.52, P < 0.01) and mean (r = 0.39, P < 0.05) anaerobic swimming power. Total mood disturbance was correlated (r = -0.34, P < 0.05) with mean swimming power. The results suggest that neurological mechanisms play a role in the adaptations that result from periodized training.

Bone mineral content and menstrual regularity in female runners.

The relationship between bone mineral content and menstrual regularity in 10 amenorrheic runners (0-3 menses during the past year), 12 runners with regular menstrual cycles (10-12 menses during the past year), and 15 non-athletic women with regular menstrual cycles was investigated. Comparisons of the two groups of runners indicated no significant differences in body fatness, average weekly running distance, or average daily intake of calcium (Ca), phosphorus (P), and Ca/P ratios. Mean bone mineral content for the three groups, measured by photon absorptiometry, was 0.508, 0.529, and 0.544 g X cm-2, respectively, at 3 cm distal radius, and 0.707, 0.700, and 0.707 g X cm-2, respectively, at one-third distal radius, indicating no significant differences among the groups (P less than 0.05). However, a significant relationship (r = 0.77) was noted between bone mineral content and body fatness only in the amenorrheic runners. Within the amenorrheic population, the five thinnest runners had significantly lower mean bone mineral content values at 3 cm distal radius (0.457 g X cm-2) than the five runners with higher relative body fatness (0.559 g X cm-2). We conclude, therefore, that amenorrhea, independent of body composition, was not related to reduced bone mineral content in female runners. However, the combination of excessive thinness and amenorrhea may, in fact, predispose female athletes to reduced bone mass.

Degree of arterial desaturation in normoxia influences VO2max decline in mild hypoxia.

PURPOSE Elite endurance athletes display varying degrees of pulmonary gas exchange limitations during maximal normoxic exercise and many demonstrate reduced arterial O2 saturations (SaO2) at VO2max--a condition referred to as exercise induced arterial hypoxemia (EIH). We asked whether mild hypoxia would cause significant declines in SaO2 and VO2max in EIH athletes while non-EIH athletes would be unaffected. METHODS Nineteen highly trained males were divided into EIH (N = 8) or Non-EIH (N = 6) groups based on SaO2 at VO2max (EIH <90%, Non-EIH >92%). Athletes with intermediate SaO2 values (N = 5) were only included in correlational analyses. Two randomized incremental treadmill tests to exhaustion were completed--one in normoxia, one in mild hypoxia (FIO2 = 0.187; approximately 1,000 m). RESULTS EIH subjects demonstrated a significant decline in VO2max from normoxia to mild hypoxia (71.1+/-5.3 vs. 68.1+/-5.0 mL x kg(-1) min(-1), P<0.01), whereas the non-EIH group did not show a significant deltaVO2max (67.2+/-7.6 vs. 66.2+/-8.4 mL x kg(-1) x min(-1)). For all 19 athletes, SaO2 during maximal exercise in normoxia correlated with the change in VO2max from normoxia to mild hypoxia (r = -0.54, P<0.05). However, the change in SaO2 and arterial O2 content from normoxia to mild hypoxia was equal for both EIH and Non-EIH (deltaSaO2 = 5.2% for both groups), bringing into question the mechanism by which changes in SaO2 affect VO2max in mild hypoxia. CONCLUSIONS We conclude that athletes who display reduced measures of SaO2 during maximal exercise in normoxia are more susceptible to declines in VO2max in mild hypoxia compared with normoxemic athletes.

Characteristics of the control of human thermoregulatory behavior

The aim of this study was to characterize several of the thermal input(s) that influence thermo-behavior in humans. Eight male subjects completed two trials in which they were free to initiate an exit from a hot chamber (45 degrees C) to a cold chamber (10 degrees C; H-->C) or from a cold chamber to a hot chamber (C-->H). Upon initiating an exit from the chamber, mean skin temperature (T(Sk)), rectal temperature (T(Rectal)), subjective thermal comfort, and time in the climate chambers prior to exit were recorded. Thermo-behavior was defined as the initiation of exit. All variables were similar (P> or =0.05) between the two trials. T(Sk) and thermal comfort at H-->C were significantly (P</=0.05) higher (34.0+/-1.1 degrees C, and 7.3+/-0.6, respectively) than at C-->H (29.4+/-0.9 degrees C, and 3.0+/-0.6, respectively). No significant differences (P> or =0.05) were found between H-->C and C-->H for T(Rectal) (H-->C: 37.0+/-0.2 degrees C vs. C-->H: 37.0+/-0.2 degrees C) or time prior to exit (H-->C: 3.9+/-2.3 min vs. C-->H: 3.9+/-1.7 min). The frequency distributions and the probability of the initiation of exit curves at H-->C and C-->H for both T(Sk) and thermal comfort were significantly negatively skewed (P< or =0.05) and normally distributed, respectively (P>/=0.05). Skin temperature appears to be an important thermal input mediating thermo-behavioral responses. This behavioral response appears to be more precise when exposed to hot temperatures compared to cold temperatures.

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.

The effect of exercise modality on exercise-induced hypoxemia

To investigate the effect of exercise mode on arterial oxyhemoglobin saturation (SaO2), 13 healthy, actively training men who displayed exercise-induced hypoxemia (EIH) performed two incremental maximal exercise tests: uphill treadmill running and cycle ergometry. At maximum, treadmill running resulted in a lower SaO2 (88.6+/-2% versus 92.6+/-2.0%) a lower ventilatory equivalent for carbon dioxide (VE/VCO2; 28.8+/-0.6 versus 31.2+/-0.9), and a higher maximal oxygen consumption (VO2, MAX; 4.83+/-0.11 l x min(-1) versus 4.61+/-0.14 l x min(-1) when compared to cycle ergometry. When data were combined from maximal running and cycling. SaO2 was correlated to VE/VCO2 (r = 0.54). However, there was no relationship between the differences in SaO2 and ventilation between exercise modes. This suggests that ventilation is important in the maintenance of SaO2, but that the difference observed in SaO2 between treadmill running and cycle ergometry cannot be explained by differences in ventilation and must be due to differences in diffusion limitation or ventilation-perfusion inequality.

Lung Volumes and Maximal Respiratory Pressures in Collegiate Swimmers and Runners

To determine whether respiratory muscle strength is related to pulmonary volume differences in athletes and nonathletes, 11 intercollegiate female swimmers, 11 female cross-country runners, and two nonathletic control groups, matched to the athletes in height and age, were evaluated for pulmonary parameters including maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax). Swimmers exhibited larger (p less than .05) vital capacities (VC), residual lung volumes (RV), inspiratory capacities (IC), and functional residual capacities (FRC) than both the runners or the controls but no difference (p greater than .05) in either PImax or inspiratory flow (FIV 25%-75%). Timed expiratory volumes (FEV 0.5 and FEV 1.0) were significantly (p less than .05) lower in the swimmers than in the controls. These data suggest that an adaptational growth may be responsible, in part, for the augmented static lung volumes demonstrated in swimmers.

Ventilation's role in the decline in VO2max and SaO2 in acute hypoxic exercise

The role of ventilation in the response in aerobic capacity and arterial oxygen saturation (SaO2) to acute hypoxic exercise was studied in 13 healthy active men divided into two groups based on their normoxic maximal exercise VE/VO2 (LOW < or =27.7; HIGH > or = 30.2) and PAO2 estimates (LOW < or = 107 mm Hg; HIGH > or = 110 mm Hg). Groups performed two incremental progressive maximal cycle exercise (VO2max) tests: normoxia (FIO2 = 20.9%) and acute hypoxia (FIO2 = 13.3%). To evaluate the influence of hypoxic ventilatory drive on ventilation, resting hypoxic ventilatory response (rHVR) was measured. LOW demonstrated lower ventilatory responses (VE, VE/VO2, and VE/VCO2) during both normoxic and hypoxic exercise (P < or = 0.05). During maximal hypoxic exercise, LOW had a greater decline in both VO2max (21.6 mL x kg(-1) x min(-1) vs 16.6 mL x kg(-1) x min[-1]) and SaO2 (31.9% vs 22.1%). Modest but significant correlations were identified between normoxic VE/VO2 and the decline in both VO2max (r = -0.62) and SaO2 (r = -0.60). No correlations were identified between rHVR and any ventilatory response or SaO2. In summary, the results from this study suggest that a low exercise-induced hyperventilatory response is a significant mechanism in the arterial desaturation observed during hypoxic exercise and the decline in aerobic capacity associated with this desaturation. However, the ventilatory response to hypoxic exercise is not dependent upon hypoxic ventilatory drive.