Gender-based differences in substrate use during exercise at a self-selected pace

The aim of this study was to investigate gender-based differences in substrate use during exercise at a self-selected pace. Seventeen men and 17 women performed a maximal exercise test and a 20-minute bout of self-paced treadmill walking to determine carbohydrate and fat oxidation rates. Gas exchange measurements were performed throughout the tests, and stoichiometric equations were used to calculate substrate oxidation rates. For each individual, a best-fit polynomial curve was constructed using fat oxidation rate (g·min(-1)) vs. exercise intensity (percentage of maximal oxygen uptake, % VO(2)max). Each individual curve was used to obtain the following variables: maximal fat oxidation (MFO), the peak rate of fat oxidation measured over the entire range of exercise intensities; fat(max), the exercise intensity at which the MFO was observed; and fat(max) zone, range of exercise intensities with fat oxidation rates within 10% of fat oxidation rates at fat(max). Although the MFO was similar between genders, fat(max) was lower in men than in women. Similarly, the "low" and "high" borders of the fat(max) zone were lower in men than in women. During exercise at a self-selected pace, carbohydrate oxidation rates were greater in men than in women, despite no gender-based differences in fat oxidation rates. However, fat oxidation contribution to total energy expenditure (EE) was greater in women than in men, despite no gender-based differences in the exercise intensity. In conclusion, although both genders self-selected a similar exercise intensity, the contribution of fat oxidation to EE is greater in women than in men. Interestingly, both genders self-selected an exercise intensity that falls within the fat(max) zone.     

Gender differences in hockey players during on-ice graded exercise

The purpose of this study was to examine whether gender differences exist for ventilatory threshold (VT), lactate threshold (LT), and Vo2max during on-ice skating in college hockey players. Ten male and 10 female Division III college hockey players performed a graded exercise skating protocol until reaching volitional fatigue. The graded exercise test employed stages that were 80 seconds in duration, with 40 seconds of rest between each stage to obtain blood lactate samples. Ventilatory threshold occurred at a higher percentage of maximal heart rate (HRmax) in women than in men. The women's VT occurred at 77.3% +/- 1.6% HRmax, while the men's VT occurred at 72.6% +/- 2.0% HRmax (p < 0.02). Men and women had similar HRmax values: 191.3 +/- 2.5 b.min and 185.8 +/- 2.5 b.min, respectively. Vo2max was different between genders, with men at 52.7 +/- 1.3 mL.kg.min and women at 40.1 +/- 1.0 mL.kg.min (p < 0.01). In addition, VT was different between genders when measured as a percentage of Vo2max, with men at 52.7% +/- 3.2% and women at 67.3% +/- 4.0% (p < 0.02). In contrast, LT was similar between genders when expressed as a percentage of HRmax or Vo2max. For each gender, LT occurred at a significantly higher percentage of HRmax or Vo2max than VT did. It can be concluded that VT does not accurately predict LT in male or female hockey players. Additionally, competitive female hockey players have a lower Vo2max but a higher VT than their male counterparts. An increased VT may be a compensatory mechanism to offset the smaller Vo2max values measured in female hockey players. On-ice testing is a practical way to address specific aerobic training needs of hockey players.     

Longitudinal changes in aerobic power in older men and women.

The purpose of this study was to describe the longitudinal (10 yr) decline in aerobic power [maximal O(2) uptake (Vo(2 max))] and anaerobic threshold [ventilatory threshold (T(Ve))] of older adults living independently in the community. Ten years after initial testing, 62 subjects (34 men, mean age 73.5 +/- 6.4 yr; 28 women, 72.1 +/- 5.3 yr) achieved Vo(2 max) criteria during treadmill walking tests to the limit of tolerance, with T(Ve) determined in a subset of 45. Vo(2 max) in men showed a rate of decline of -0.43 ml.kg(-1).min(-1).yr(-1), and the decline in Vo(2 max) was consequent to a lowered maximal heart rate with no change in the maximum O(2) pulse. The women showed a slower rate of decline of Vo(2 max) of -0.19.ml.kg(-1).min(-1).yr(-1) (P < 0.05), again with a lowered HR(max) and unchanged O(2) pulse. In this sample, lean body mass was not changed over the 10-yr period. Changes in Vo(2 max) were not significantly related to physical activity scores. T(Ve) showed a nonsignificant decline in both men and women. Groupings of young-old (65-72 yr at follow-up) vs. old-old (73-90 yr at follow-up) were examined. In men, there were no differences in the rate of Vo(2 max) decline. The young-old women showed a significant decline in Vo(2 max), whereas old-old women, initially at a Vo(2 max) of 19.4 +/- 3.1 ml.kg(-1).min(-1), showed no loss in Vo(2 max). The longitudinal data, vs. cross-sectional analysis, showed a greater decline for men but similar estimates of the rates of change in women. Thus the 10-yr longitudinal study of the cohort of community-dwelling older adults who remained healthy, ambulatory, and independent showed a 14% decline in Vo(2 max) in men, and a smaller decline of 7% in women, with the oldest women showing little change over the 10-yr period.     

Markers of inflammation are inversely associated with VO2 max in asymptomatic men.

We investigated whether markers of inflammation, including a cytokine (IL-6), acute-phase reactants [C-reactive protein (CRP) and fibrinogen], and white blood cell (WBC) count are associated with maximal O(2) consumption (Vo(2 max)) in men without coronary heart disease (CHD). In asymptomatic men (n = 172, 51 +/- 9.3 yr old), Vo(2 max) was measured during a symptom-limited graded treadmill exercise test. Physical activity level was assessed by a standardized questionnaire. IL-6 and CRP were measured by immunoassays, fibrinogen by the Clauss method, and WBC count with a Coulter counter. IL-6 and CRP were logarithmically transformed to reduce skewness. Multivariable regression was used to assess whether markers of inflammation were associated with Vo(2 max) after adjustment for age, body mass index, CHD risk factors, and lifestyle variables (physical activity level, percent body fat, and alcohol intake). Vo(2 max) was 34.5 ml.kg(-1).min(-1) (SD 6.1). Log IL-6 (r = -0.38, P < 0.001), log CRP (r = -0.40, P < 0.001), fibrinogen (r = -0.42, P < 0.001), and WBC count (r = -0.22, P = 0.004) were each correlated with Vo(2 max). In separate multivariable linear regression models that adjusted for age, body mass index, CHD risk factors, and lifestyle variables, log IL-6 [beta-coeff = -1.66 +/- 0.63 (SE), P = 0.010], log CRP [beta-coeff = -0.99 +/- 0.33 (SE), P = 0.003], fibrinogen [beta-coeff = -1.51 +/- 0.44 (SE), P = 0.001], and WBC count [beta-coeff = -0.52 +/- 0.30 (SE), P = 0.088] were each inversely associated with Vo(2 max). In conclusion, higher circulating levels of IL-6, CRP, and fibrinogen are independently associated with lower Vo(2 max) in asymptomatic men.     

Exercise and diet enhance fat oxidation and reduce insulin resistance in older obese adults.

Older, obese, and sedentary individuals are at high risk of developing diabetes and cardiovascular disease. Exercise training improves metabolic anomalies associated with such diseases, but the effects of caloric restriction in addition to exercise in such a high-risk group are not known. Changes in body composition and metabolism during a lifestyle intervention were investigated in 23 older, obese men and women (aged 66 +/- 1 yr, body mass index 33.2 +/- 1.4 kg/m(2)) with impaired glucose tolerance. All volunteers undertook 12 wk of aerobic exercise training [5 days/wk for 60 min at 75% maximal oxygen consumption (Vo(2max))] with either normal caloric intake (eucaloric group, 1,901 +/- 277 kcal/day, n = 12) or a reduced-calorie diet (hypocaloric group, 1,307 +/- 70 kcal/day, n = 11), as dictated by nutritional counseling. Body composition (decreased fat mass; maintained fat-free mass), aerobic fitness (Vo(2max)), leptinemia, insulin sensitivity, and intramyocellular lipid accumulation (IMCL) in skeletal muscle improved in both groups (P < 0.05). Improvements in body composition, leptin, and basal fat oxidation were greater in the hypocaloric group. Following the intervention, there was a correlation between the increase in basal fat oxidation and the decrease in IMCL (r = -0.53, P = 0.04). In addition, basal fat oxidation was associated with circulating leptin after (r = 0.65, P = 0.0007) but not before the intervention (r = 0.05, P = 0.84). In conclusion, these data show that exercise training improves resting substrate oxidation and creates a metabolic milieu that appears to promote lipid utilization in skeletal muscle, thus facilitating a reversal of insulin resistance. We also demonstrate that leptin sensitivity is improved but that such a trend may rely on reducing caloric intake in addition to exercise training.     

Exercise training increases intramyocellular lipid and oxidative capacity in older adults

Intramyocellular lipid (IMCL) has been associated with insulin resistance. However, an association between IMCL and insulin resistance might be modulated by oxidative capacity in skeletal muscle. We examined the hypothesis that 12 wk of exercise training would increase both IMCL and the oxidative capacity of skeletal muscle in older (67.3 +/- 0.7 yr), previously sedentary subjects (n = 13; 5 men and 8 women). Maximal aerobic capacity (Vo(2 max)) increased from 1.65 +/- 0.20 to 1.85 +/- 0.14 l/min (P < 0.05), and systemic fat oxidation induced by 1 h of cycle exercise at 45% of Vo(2 max) increased (P < 0.05) from 15.03 +/- 40 to 19.29 +/- 0.80 (micromol.min(-1).kg fat-free mass(-1)). IMCL, determined by quantitative histological staining in vastus lateralis biopsies, increased (P < 0.05) from 22.9 +/- 1.9 to 25.9 +/- 2.6 arbitrary units (AU). The oxidative capacity of muscle, determined by succinate dehydrogenase staining intensity, significantly increased (P < 0.05) from 75.2 +/- 5.2 to 83.9 +/- 3.6 AU. The percentage of type I fibers significantly increased (P < 0.05) from 35.4 +/- 2.1 to 40.1 +/- 2.3%. In conclusion, exercise training increases IMCL in older persons in parallel with an enhanced capacity for fat oxidation.     

Muscle fatty acid oxidative capacity is a determinant of whole body fat oxidation in elderly people

In sedentary elderly people, a reduced muscle fatty acid oxidative capacity (MFOC) may explain a decrease in whole body fat oxidation. Eleven sedentary and seven regularly exercising subjects (65.6 +/- 4. 5 yr) were characterized for their aerobic fitness [maximal O(2) uptake (VO(2 max))/kg fat free mass (FFM)] and their habitual daily physical activity level [free-living daily energy expenditure divided by sleeping metabolic rate (DEE(FLC)/SMR)]. MFOC was determined by incubating homogenates of vastus lateralis muscle with [1-(14)C]palmitate. Whole body fat oxidation was measured by indirect calorimetry over 24 h. MFOC was 40.4 +/- 14.7 and 44.3 +/- 16.3 nmol palmitate. g wet tissue(-1). min(-1) in the sedentary and regularly exercising individuals, respectively (P = nonsignificant). MFOC was positively correlated with DEE(FLC)/SMR (r = 0.58, P < 0. 05) but not with VO(2 max)/kg FFM (r = 0.35, P = nonsignificant). MFOC was the main determinant of fat oxidation during all time periods including physical activity. Indeed, MFOC explained 19.7 and 30.5% of the variance in fat oxidation during walking and during the alert period, respectively (P < 0.05). Furthermore, MFOC explained 23.0% of the variance in fat oxidation over 24 h (P < 0.05). It was concluded that, in elderly people, MFOC may be influenced more by overall daily physical activity than by regular exercising. MFOC is a major determinant of whole body fat oxidation during physical activities and, consequently, over 24 h.     

Plasma FFA responses to prolonged walking in untrained men and women

Gender differences in plasma FFA responses to 90 min of treadmill walking at 35% VO2max were investigated in six men and six women following an overnight fast. The subjects represented average values for maximal oxygen uptake and body fat percentage for age and gender. Mean plasma FFA concentration at 45 and 90 min of exercise were significantly (P less than 0.05) higher for women (0.82 mmol X 1(-1), 0.88 mmol X 1(-1)) than men (0.42 mmol X 1(-1), 0.59 mmol X 1(-1)). Lower R values for women throughout the exercise period indicated a greater percentage fat in total metabolism than for men while the FFA/glycerol results supported greater lipolytic activity for women. The uniformity of percent fat in metabolism for women from rest to exercise showed that FFA release from adipose tissue increased rapidly with the onset of exercise which was not the case for men. Comparison of metabolic data as well as a statistical analysis (ANCOVA) controlling for the influence of VO2max and percentage body fat on FFA plasma concentration suggested that gender differences in FFA responses to prolonged submaximal exercise can be expected to occur in untrained subjects.     

Determinants of insulin-stimulated glucose disposal in middle-aged, premenopausal women

Controversy exists regarding the relative importance of adiposity, physical fitness, and physical activity in the regulation of insulin-stimulated glucose disposal. To address this issue, we measured insulin-stimulated glucose disposal [mg. kg fat-free mass (FFM)(-1). min(-1); oxidative and nonoxidative components] in 45 nondiabetic, nonobese, premenopausal women (mean +/- SD; 47 +/- 3 yr) by use of hyperinsulinemic euglycemic clamp (40 mU. m(-2). min(-1)) and [6,6-2H2]glucose dilution techniques. We also measured body composition, abdominal fat distribution, thigh muscle fat content, maximal oxygen consumption (VO2 max), and physical activity energy expenditure ((2)H(2)(18)O kinetics) as possible correlates of glucose disposal. VO2 max was the strongest correlate of glucose disposal (r = 0.63, P < 0.01), whereas whole body and abdominal adiposity showed modest associations (range of r values from -0.32 to -0.46, P < 0.05 to P < 0.01). A similar pattern of correlations was observed for nonoxidative glucose disposal. None of the variables measured correlated with oxidative glucose disposal. The relationship of VO2 max to glucose disposal persisted after statistical control for FFM, percent body fat, and intra-abdominal fat (r = 0.40, P < 0.01). In contrast, correlations of total and regional adiposity measures to insulin sensitivity were no longer significant after statistical adjustment for VO2 max. VO2 max was the only variable to enter stepwise regression models as a significant predictor of total and nonoxidative glucose disposal. Our results highlight the importance of VO2 max as a determinant of glucose disposal and suggest that it may be a stronger determinant of variation in glucose disposal than total and regional adiposity in nonobese, nondiabetic, premenopausal women.     

Gender differences in the decline in aerobic capacity and its physiological determinants during the later decades of life.

We investigated the hemodynamic determinants of the age-associated decline in maximal oxygen uptake (V(O2 max)) and the influence of gender on the decline in V(O2 max) and its determinants in old and very old men and women. Sedentary, 60- to 92-yr-old women (n = 71) and men (n = 29), with no evidence of cardiovascular disease, underwent maximal treadmill exercise tests during which V(O2 max) and maximal cardiac output (Q(max)) were determined. V(O2 max) and age were inversely related in both women (-23 +/- 2 ml.min(-1).yr(-1); P < 0.0001) and men (-57 +/- 5 ml.min(-1).yr(-1); P < 0.0001). The absolute slope of the V(O2 max) vs. age relationship was twofold steeper in men than in women (P < 0.0001). Q(max) was also inversely related to age in a gender-specific manner (women = -87 +/- 25 ml.min(-1).yr(-1), P = 0.0009; men = -215 +/- 50 ml.min(-1).yr(-1), P = 0.0002; P = 0.01 women vs. men). Age-related changes in maximal exercise arteriovenous oxygen content difference (a-vD(O2)) were marginally different (P = 0.08) between women (-0.12 +/- 0.03 ml.dl(-1).yr(-1), P = 0.0003) and men (-0.22 +/- 0.04 ml.dl(-1).yr(-1), P < 0.0001). Age-associated decreases in Q(max) and a-vD(O2) contributed equally to the declines in V(O2 max) in both men and women. In the later stages of life, V(O2 max), Q(max), and a-vD(O2) decrease with age more rapidly in older men than they do in older women. As a result, the gender differences dissipate in the later decades of life. Declines in Q(max) and a-vD(O2) contribute equally to the age-related decrease in V(O2 max) in men and women.     

Effects of basic training in the British Army on regular and reserve army personnel

The aim of this study was to compare changes in aerobic fitness and body composition in response to British Army (regular) and Territorial Army (reserve) basic training. Eleven regular recruits, 14 reserve recruits, and 20 controls completed the study (all males). Initially, reserve recruits were significantly older and heavier and had greater fat-free mass (FFM; 64.6 vs. 59.3 kg) and lower maximal oxygen uptake (Vo(2)max; 39.1 vs. 43.9 ml.kg(-1).min(-1)) than regular recruits. Both regular and reserve training significantly increased FFM and Vo(2)max and decreased percentage body fat. Regular training produced a greater increase in Vo(2)max than reserve training (13.1 vs. 7.6%, p < 0.0005). Reserve training produced a greater increase in body mass (2.2 vs. 0.9 kg, p = 0.019) and tended to produce a greater increase in FFM (2.6 vs. 1.6 kg, p = 0.062). Although both training programs improve aerobic fitness and body composition, increasing the volume of physical training in the reserve training program would probably enhance the training adaptations achieved.     

Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation.

The aim of this study was to determine the effects of exercise at different intensities on 24-h energy expenditure (EE) and substrate oxidation. Sixteen adults (8 men and 8 women) were studied on three occasions [sedentary day (Con), a low-intensity exercise day (LI; 400 kcal at 40% of maximal oxygen consumption) and a high-intensity exercise day (HI; 400 kcal at 70% of maximal oxygen consumption)] by using whole room indirect calorimetry. Both 24-h EE and carbohydrate oxidation were significantly elevated on the exercise days (Con < LI = HI), but 24-h fat oxidation was not different across conditions. Muscle enzymatic profile was not consistently related to 24-h fat or carbohydrate oxidation. With further analysis, it was found that, compared with men, women sustained slightly higher rates of 24-h fat oxidation (mg x kg FFM(-1) x min(-1)) and had a muscle enzymatic profile favoring fat oxidation. It is concluded that exercise intensity has no effect on 24-h EE or nutrient oxidation. Additionally, it appears that women may sustain slightly greater 24-h fat oxidation rates during waking and active periods of the day.     

The potential for mitochondrial fat oxidation in human skeletal muscle influences whole body fat oxidation during low-intensity exercise

The purpose of this study was to investigate fatty acid (FA) oxidation in isolated mitochondrial vesicles (mit) and its relation to training status, fiber type composition, and whole body FA oxidation. Trained (Vo(2 peak) 60.7 +/- 1.6, n = 8) and untrained subjects (39.5 +/- 2.0 ml.min(-1).kg(-1), n = 5) cycled at 40, 80, and 120 W, and whole body relative FA oxidation was assessed from respiratory exchange ratio (RER). Mit were isolated from muscle biopsies, and maximal ADP stimulated respiration was measured with carbohydrate-derived substrate [pyruvate + malate (Pyr)] and FA-derived substrate [palmitoyl-l-carnitine + malate (PC)]. Fiber type composition was determined from analysis of myosin heavy-chain (MHC) composition. The rate of mit oxidation was lower with PC than with Pyr, and the ratio between PC and Pyr oxidation (MFO) varied greatly between subjects (49-93%). MFO was significantly correlated to muscle fiber type distribution, i.e., %MHC I (r = 0.62, P = 0.03), but was not different between trained (62 +/- 5%) and untrained subjects (72 +/- 2%). MFO was correlated to RER during submaximal exercise at 80 (r = -0.62, P = 0.02) and 120 W (r = -0.71, P = 0.007) and interpolated 35% Vo(2 peak) (r = -0.74, P = 0.004). ADP sensitivity of mit respiration was significantly higher with PC than with Pyr. It is concluded that MFO is influenced by fiber type composition but not by training status. The inverse correlation between RER and MFO implies that intrinsic mit characteristics are of importance for whole body FA oxidation during low-intensity exercise. The higher ADP sensitivity with PC than that with Pyr may influence fuel utilization at low rate of respiration.     

Physical fitness profile of Army ROTC cadets

One role of Army Reserved Officer's Training Corps (ROTC) programs is to physically prepare cadets for the demands of a military career. Cadets participate in physical training 3 days per week as part of their military science curriculum. Limited research has been conducted on the fitness level of ROTC cadets; therefore, the purpose of this study was to profile the physical fitness status of a cadre of ROTC cadets. Forty-three cadets (30 men and 13 women) performed Army Physical Fitness Test (APFT) assessments (2-mile run, 2-minute maximum push-ups and sit-ups) and clinical assessments of fitness (Bruce protocol Vo(2)max, underwater weighing, and 1 repetition maximum [1RM] bench press tests). Mean +/- standard deviations were calculated to provide the physical fitness profile for each parameter. Male cadets (21 +/- 2.2 years; height 177.4 +/- 6.6 cm; mass 79.2 +/- 9.4 kg) scored 49.6 +/- 6.1 ml.kg(-1).min(-1) for Vo(2)max, 14.8 +/- 4.2% fat, 86.5 +/- 24.9 kg 1RM bench press, 2-mile run of 13.97 +/- 1.4 minutes, 70.5 +/- 12.8 sit-ups, and 60.2 +/- 13.2 push-ups. Female cadets (20 +/- 2.4 years; height 165.1 +/- 8.0 cm; mass 63.5 +/- 10.0 kg) scored 40.8 +/- 3.9 ml.kg(-1).min(-1) for Vo(2) max, 23.9 +/- 3.8% fat, 35.3 +/- 8.2 kg 1RM bench press, 2-mile run of 17.0 +/- 1.6 minutes, 65.0 +/- 12.9 sit-ups, and 33.3 +/- 11.2 push-ups. The mean scores were above the 83rd percentile on all APFT items and average (percent fat) to above average (Vo(2)max and men's bench press scores) when compared with peer-age and sex-corrected norms. Only the women's bench press score was below average. With the exception of the women's bench press, these ROTC cadets possessed average to above average levels of fitness.     

Greater rate of decline in maximal aerobic capacity with age in endurance-trained than in sedentary men.

To determine the relation between habitual endurance exercise status and the age-associated decline in maximal aerobic capacity [i.e., maximal O(2) consumption (Vo(2 max))] in men, we performed a well-controlled cross-sectional laboratory study on 153 healthy men aged 20-75 yr: 64 sedentary and 89 endurance trained. Vo(2 max) (ml. kg(-1). min(-1)), measured by maximal treadmill exercise, was inversely related to age in the endurance-trained (r = -0.80) and sedentary (r = -0.74) men but was higher in the endurance-trained men at any age. The rate of decline in Vo(2 max) with age (ml. kg(-1). min(-1)) was greater (P < 0.001) in the endurance-trained than in the sedentary men. Whereas the relative rate of decline in Vo(2 max) (percent decrease per decade from baseline levels in young adulthood) was similar in the two groups, the absolute rate of decline in Vo(2 max) was -5.4 and -3.9 ml. kg(-1). min(-). decade(-1) in the endurance-trained and sedentary men, respectively. Vo(2 max) declined linearly across the age range in the sedentary men but was maintained in the endurance-trained men until approximately 50 yr of age. The accelerated decline in Vo(2 max) after 50 yr of age in the endurance-trained men was related to a decline in training volume (r = 0.46, P < 0.0001) and was associated with an increase in 10-km running time (r = -0.84, P < 0.0001). We conclude that the rate of decline in maximal aerobic capacity during middle and older age is greater in endurance-trained men than in their sedentary peers and is associated with a marked decline in O(2) pulse.     

Relation of heart rate to percent VO2 peak during submaximal exercise in the heat.

We tested the hypothesis that elevation in heart rate (HR) during submaximal exercise in the heat is related, in part, to increased percentage of maximal O(2) uptake (%Vo(2 max)) utilized due to reduced maximal O(2) uptake (Vo(2 max)) measured after exercise under the same thermal conditions. Peak O(2) uptake (Vo(2 peak)), O(2) uptake, and HR during submaximal exercise were measured in 22 male and female runners under four environmental conditions designed to manipulate HR during submaximal exercise and Vo(2 peak). The conditions involved walking for 20 min at approximately 33% of control Vo(2 max) in 25, 35, 40, and 45 degrees C followed immediately by measurement of Vo(2 peak) in the same thermal environment. Vo(2 peak) decreased progressively (3.77 +/- 0.19, 3.61 +/- 0.18, 3.44 +/- 0.17, and 3.13 +/- 0.16 l/min) and HR at the end of the submaximal exercise increased progressively (107 +/- 2, 112 +/- 2, 120 +/- 2, and 137 +/- 2 beats/min) with increasing ambient temperature (T(a)). HR and %Vo(2 peak) increased in an identical fashion with increasing T(a). We conclude that elevation in HR during submaximal exercise in the heat is related, in part, to the increase in %Vo(2 peak) utilized, which is caused by reduced Vo(2 peak) measured during exercise in the heat. At high T(a), the dissociation of HR from %Vo(2 peak) measured after sustained submaximal exercise is less than if Vo(2 max) is assumed to be unchanged during exercise in the heat.     

Single bouts of exercise affect albumin redox state and carbonyl groups on plasma protein of trained men in a workload-dependent manner.

The purpose of this study was to investigate the effect of single bouts of exercise at three different intensities on the redox state of human serum albumin (HSA) and on carbonyl groups on protein (CP) concentrations in plasma. Trained men [n = 44, maximal oxygen consumption (Vo(2max)): 55 +/- 5 ml.kg(-1).min(-1), nonsmokers, 34 +/- 5 years of age] from a homogenous population, volunteers from a police special forces unit, were randomly assigned to perform on a cycle ergometer either at 70% (n = 14), 75% (n = 14), or 80% (n = 16) of Vo(2max) for 40 min. Blood was collected before exercise, immediately after the exercise test (IE), and 30 min after each test (30M) and 30 h after each test (30H). The reduced fraction of HSA, human mercaptalbumin (HMA), decreased at all three exercise intensities IE and 30M, returning to preexercise values by 30H (P < 0.05). HMA was primarily oxidized to its reversible fraction human nonmercaptalbumin 1 (HNA1). CP concentrations increased at 75% of Vo(2max) IE and 30M with a tendency (P < 0.1) and at 80% Vo(2max) IE and 30M significantly, returning to preexercise concentrations by 30H (P < 0.01). These results indicate that the HSA redox system in plasma is activated after a single bout of cycle ergometer exercise at 70% Vo(2max) and 40 min duration. The extent of the HSA modification increased with exercise intensity. Oxidative protein damage, as indicated by CP, was only significantly increased at 80% Vo(2max) intensity in this homogenous cohort of trained men.     

Oxidation of nonplasma fatty acids during exercise is increased in women with abdominal obesity.

We evaluated plasma fatty acid availability and plasma and whole body fatty acid oxidation during exercise in five lean and five abdominally obese women (body mass index = 21 +/- 1 vs. 38 +/- 1 kg/m(2)), who were matched on aerobic fitness, to test the hypothesis that obesity alters the relative contribution of plasma and nonplasma fatty acids to total energy production during exercise. Subjects exercised on a recumbent cycle ergometer for 90 min at 54% of their peak oxygen consumption. Stable isotope tracer methods ([(13)C]palmitate) were used to measure fatty acid rate of appearance in plasma and the rate of plasma fatty acid oxidation, and indirect calorimetry was used to measure whole body substrate oxidation. During exercise, palmitate rate of appearance increased progressively and was similar in obese and lean groups between 60 and 90 min of exercise [3.9 +/- 0.4 vs. 4.0 +/- 0.3 micromol. kg fat free mass (FFM)(-1). min(-1)]. The rate of plasma fatty acid oxidation was also similar in obese and lean subjects (12.8 +/- 1.7 vs. 14.5 +/- 1.8 micromol. kg FFM(-1). min(-1); P = not significant). However, whole body fatty acid oxidation during exercise was 25% greater in obese than in lean subjects (21.9 +/- 1.2 vs. 17.5 +/- 1.6 micromol. kg FFM(-1). min(-1); P < 0.05). These results demonstrate that, although plasma fatty acid availability and oxidation are similar during exercise in lean and obese women, women with abdominal obesity use more fat as a fuel by oxidizing more nonplasma fatty acids.     

A new non-exercise-based Vo2max prediction equation for aerobically trained men

The purposes of the present study were to (a) modify previously published Vo(2)max equations using the constant error (CE = mean difference between actual and predicted Vo(2)max) values from Malek et al. (28); (b) cross-validate the modified equations to determine their accuracy for estimating Vo(2)max in aerobically trained men; (c) derive a new non- exercise-based equation for estimating Vo(2)max in aerobically trained men if the modified equations are not found to be accurate; and (d) cross-validate the new Vo(2)max equation using the predicted residual sum of squares (PRESS) statistic and an independent sample of aerobically trained men. One hundred and fifty-two aerobically trained men (Vo(2)max mean +/- SD = 4,154 +/- 629 ml.min(-1)) performed a maximal incremental test on a cycle ergometer to determine actual Vo(2)max. An aerobically trained man was defined as someone who had participated in continuous aerobic exercise 3 or more sessions per week for a minimum of 1 hour per session for at least the past 18 months. Nine previously published Vo(2)max equations were modified for use with aerobically trained men. The predicted Vo(2)max values from the 9 modified equations were compared to actual Vo(2)max by examining the CE, standard error of estimate (SEE), validity coefficient (r), and total error (TE). Cross-validation of the modified non-exercise-based equations on a random subsample of 50 subjects resulted in a %TE > or = 13% of the mean of actual Vo(2)max. Therefore, the following non-exercise-based Vo(2)max equation was derived from a random subsample of 112 subjects: Vo(2)max (ml.min(-1)) = 27.387(weight in kg) + 26.634(height in cm) - 27.572(age in years) + 26.161(h.wk(-1) of training) + 114.904(intensity of training using the Borg 6-20 scale) + 506.752(natural log of years of training) - 4,609.791 (R = 0.82, R(2) adjusted = 0.65, and SEE = 378 ml.min(-1)). Cross-validation of this equation on the remaining sample of 40 subjects resulted in a %TE of 10%. Therefore, the non-exercise-based equation derived in the present study is recommended for estimating Vo(2)max in aerobically trained men.     

Relationship between resting ventilatory chemosensitivity and maximal oxygen uptake in moderate hypobaric hypoxia.

This study tested the hypothesis that the extent of the decrement in (.)Vo(2max) and the respiratory response seen during maximal exercise in moderate hypobaric hypoxia (H; simulated 2,500 m) is affected by the hypoxia ventilatory and hypercapnia ventilatory responses (HVR and HCVR, respectively). Twenty men (5 untrained subjects, 7 long distance runners, 8 middle distance runners) performed incremental exhaustive running tests in H and normobaric normoxia (N) condition. During the running test, (.)Vo(2), pulmonary ventilation (Ve) and arterial oxyhemoglobin saturation (Sa(O(2))) were measured, and in two ventilatory response tests performed during N, a rebreathing method was used to evaluate HVR and HCVR. Mean HVR and HCVR were 0.36 +/- 0.04 and 2.11 +/- 0.2 l.min(-1).mmHg(-1), respectively. HVR correlated significantly with the percent decrements in (.)Vo(2max) (%d(.)Vo(2max)), Sa(O(2)) [%dSa(O(2)) = (N-H).N(-1).100], and (.)Ve/(.)Vo(2) seen during H condition. By contrast, HCVR did not correlate with any of the variables tested. The increment in maximal Ve between H and N significantly correlated with %d(.)Vo(2max). Our findings suggest that O(2) chemosensitivity plays a significant role in determining the level of exercise hyperventilation during moderate hypoxia; thus, a higher O(2) chemosensitivity was associated with a smaller drop in (.)Vo(2max) and Sa(O(2)) under those conditions.