Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability.

PURPOSE: Five days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise. METHODS: Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x d(-1) fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)). RESULTS: FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); RER was restored by 1 d CHO and CHO intake during cycling (0.90 +/- 0.01, 0.80 +/- 0.01, 0.91 +/- 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 +/- 0.01, 0.88 +/- 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 +/- 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 +/- 4 g vs 45 +/- 3 g, P < 0.05), whereas CHO oxidation was reduced (354 +/- 11 g vs 419 +/- 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 +/- 0.67 min vs 25.45 +/- 0.96 min, NS). CONCLUSION: Adaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting approximately 25 min undertaken after 2 h of submaximal cycling.     

Effect of short-term fat adaptation on high-intensity training

PURPOSE: To determine the effect of short-term (3-d) fat adaptation on high-intensity exercise training in seven competitive endurance athletes (maximal O2 uptake 5.0 +/- 0.5 L x min(-1), mean +/-SD). METHODS: Subjects consumed a standardized diet on d-0 then, in a randomized cross-over design, either 3-d of high-CHO (11 g x kg(-1)d(-1) CHO, 1 g x kg(-1) x d(-1) fat; HICHO) or an isoenergetic high-fat (2.6 g CHO x kg(-1) x d(-1), 4.6 g FAT x kg(-1) x d(-1); HIFAT) diet separated by an 18-d wash out. On the 1st (d-1) and 4th (d-4) day of each treatment, subjects completed a standardized laboratory training session consisting of a 20-min warm-up at 65% of VO2peak (232 +/- 23W) immediately followed by 8 x 5 min work bouts at 86 +/- 2% of VO2peak (323 +/- 32 W) with 60-s recovery. RESULTS: Respiratory exchange ratio (mean for bouts 1, 4, and 8) was similar on d-1 for HIFAT and HICHO (0.91 +/- 0.04 vs 0.92 +/- 0.03) and on d-4 after HICHO (0.92 +/- 0.03) but fell to 0.85 +/- 0.03 (P < 0.05) on d-4 after HIFAT. Accordingly, the rate of fat oxidation increased from 31 +/- 13 on d-1 to 61 +/- 25 micromol x kg(-1) x min(-1) on d-4 after HIFAT (P < 0.05). Blood lactate concentration was similar on d-1 and d-4 of HICHO and on d-1 of HIFAT (3.5 +/- 0.9 and 3.2 +/- 1.0 vs 3.7 +/- 1.2 mM) but declined to 2.4 +/- 0.5 mM on d-4 after HIFAT (P < 0.05). Ratings of perception of effort (legs) were similar on d-1 for HIFAT and HICHO (14.8 +/- 1.5 vs 14.1 +/- 1.4) and on d-4 after HICHO (13.8 +/- 1.8) but increased to 16.0 +/- 1.3 on d-4 after HIFAT (P < 0.05). CONCLUSIONS: 1) competitive endurance athletes can perform intense interval training during 3-d exposure to a high-fat diet, 2) such exercise elicited high rates of fat oxidation, but 3) compared with a high-carbohydrate diet, training sessions were associated with increased ratings of perceived exertion.     

Exercise and green tea extract stimulate fat oxidation and prevent obesity in mice

INTRODUCTION/PURPOSE: The purpose of the present study was to explore the combined effects of dietary supplementation with green tea extract (GTE) and regular exercise on the development of obesity in high fat-fed C57BL/6J mice. METHODS: Weight and age-matched male mice were divided into 5 groups of 10 mice each. Groups were treated as follows: a low-fat diet and not exercised (LF), a high-fat diet and not exercised (HF), a high-fat diet supplemented with GTE and not exercised (GTE-HF), a high-fat diet and exercised regularly (EX-HF), or a high-fat diet supplemented with GTE and exercised regularly (GTEEX-HF). The exercise modality was treadmill running. RESULTS: After 15 wk, GTE alone and regular exercise alone caused a 47 and 24% reduction in body weight gain induced by the high-fat diet, respectively, and when combined, resulted in an 89% reduction. In visceral fat accumulation, GTE alone, exercise alone, and their combination caused a 58, 37, and 87% reduction, respectively. Indirect calorimetry showed that the GTEEX-HF group had the highest energy expenditure and fat utilization in the sedentary condition after 4 wk. Furthermore, the GTEEX-HF group utilized more fat than the EX-HF group during exercise. GTE supplementation increased hepatic fatty acid oxidation both in the exercised and nonexercised groups. In addition, when combined with regular exercise, GTE supplementation also stimulated skeletal muscle fatty acid oxidation. CONCLUSION: In conclusion, dietary GTE and regular exercise, if combined, stimulate fat catabolism not only in the liver but also in skeletal muscle, and attenuate high-fat diet-induced obesity more effectively than each alone in C57BL/6J mice.     

Thermal and metabolic responses of high and low fat women to cold water immersion.

BACKGROUND: At rest during cold exposure, the amount of body fat plays an important role in the maintenance of core temperature. High fat (HF) individuals would therefore have an advantage as compared with their low fat (LF) counterparts. Since females usually have a higher amount of body fat than males they are expected to maintain core temperature at a lower energy cost. METHODS: The purpose of the present investigation was to dichotomize female subjects by percent fat (LF = 20.5 +/- 2%, n = 6 vs. HF = 30 +/- 3%, n = 6) to elucidate the thermal and metabolic responses during acute exposure to 17 degrees C water for 120 min. The following variables were measured: rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), oxygen consumption (VO2; ml x kg(-1) x min(-1)), and tissue insulation (I; degrees C x m2 x W(-1)). The experiment-wise error rate was set a priori at p = 0.05. RESULTS: Unexpectedly, only one of the variables demonstrated a main effect for fat (p < 0.05). Tre demonstrated a significant (p < 0.05) group by time interaction. However, Tsk and I demonstrated a main effect for time (p < 0.05). While VO2 demonstrated an increase across time, these changes were non-significant (p > 0.05). It appears that the HF group demonstrated a similar thermal (I and Tsk) and metabolic (VO2) response as compared with the LF counterparts. However, the LF groups maintained a lower Tre as compared with the HF subjects. Perhaps leaner subjects or colder water temperatures would elucidate the value of body fat in females, and demonstrate a differential response with respect to females varying in percent body fat.     

Short-term training is accompanied by a down regulation of ACC2 mRNA in skeletal muscle

Recently, we showed that short-term training induced a rapid increase in IMCL whilst insulin sensitivity tended to improve. Here we investigate molecular adaptations accompanying this physiological training-induced accumulation of IMCL. Nine untrained men (age: 23.3 +/- 3.2 y; maximal power output: 3.8 +/- 0.6 W/kg body weight) trained for two weeks. Before and after training, subjects cycled for three hours and biopsies were taken before and after exercise. mRNA concentrations of ACC2, HSL, LPL, Glut4 and HKII were quantified by RT-PCR and association of Glut4 with the membrane was quantified by immunohistochemical method. Endurance training resulted in a decrease of 29.1 % in ACC2 mRNA (p = 0.02). After training, ACC2 mRNA tended to decrease with acute exercise (- 24.4 % [p = 0.06]). HSL mRNA decreased with acute exercise after training (- 37.3 % [p = 0.002]). LPL mRNA concentrations increased with acute exercise before training (+ 42.4 % [p = 0.05]) and HKII mRNA increased with acute exercise before (+ 72.5 % [p = 0.025]) and after training (+ 99.3 % [p = 0.05]). After acute exercise, more Glut4 was associated with the membrane than before exercise, but it was not affected by training. We conclude that the training-induced increase in IMCL was accompanied by molecular adaptations in muscle to improve fat oxidative capacity, while markers of glucose metabolism were not yet changed. The present data are in line with the hypothesis that the fat oxidative capacity might be more important than the IMCL content in determining insulin sensitivity.     

Heart rate variability during exercise performed below and above ventilatory threshold

PURPOSE: To examine whether differences in heart rate variability (HRV) can distinguish sub- from supra-ventilatory-threshold exercise and whether the exercise duration at supra-threshold intensity alters cardiorespiratory synchronization. METHODS: Beat-to-beat RR interval, VO2, VCO2, VE, and blood lactate concentration of 11 healthy well-trained young subjects were collected during two exercise tests: 1) a moderate-intensity test: 15 min performed below the power at ventilatory threshold (pVT); and 2) a heavy-intensity test: above pVT until exhaustion. Fast Fourier transform, smoothed pseudo Wigner-Ville distribution, and complex demodulation were applied to RR time series. RESULTS: 1) Moderate exercise shows a prevalence of low-frequency (LF) spectral energy compared with the high-frequency (HF) one (LF = 80 +/- 10% vs HF = 20 +/- 10%, P < 0.001), whereas the reverse is observed during heavy exercise (LF = 11 +/- 8% vs HF = 89 +/- 8%, P < 0.001). 2) During heavy exercise, the HF amplitude and the tidal volume (Vt) remained constant, whereas the breathing frequency (BF) increased (BF: 0.70 +/- 0.18 vs 0.93 +/- 0.31, P < 0.01) and mean RR decreased (342 +/- 15 vs 317 +/- 16, P < 0.01). Despite the RR series and the breathing signal remaining synchronized, HR/BF ratio decreased and stabilized at 3 RR for one breathing cycle, whatever the initial ratio. CONCLUSION: 1) HRV allows us to differentiate sub- from supra-ventilatory-threshold exercise and 2) exercise duration at supra-threshold intensity does not alter the cardiorespiratory synchronization.     

Effect of exercise intensity and repetition on heart rate variability during training in elite trotting horse

RR intervals of ten elite trotting horses were recorded during an interval training session performed on track. This study examined two hypotheses. Firstly, like in humans, the hyperpnea combined with a decrease in cardiac autonomic control on heart rate during heavy exercise could result in a prevalence of high frequency heart rate variability. Secondly, this prevalence could increase with the heavy exercise repetition. Two exercise intensities were compared: moderate (ME) and heavy (HE). Furthermore, heavy exercise repetitions were compared between the beginning and the end of the interval training session. When comparing ME and HE periods: heart rate was significantly lower (155 +/- 12 vs. 210 +/- 9 ms, p < 0.001), LF spectral energy (0.04 - 0.2 Hz) was significantly higher (ME: 6.94 +/- 4.80 and HE: 0.24 +/- 0.14 ms(2) . Hz (-1), p < 0.001) whereas HF (0.2 - 2 Hz) was significantly lower (ME: 7.09 +/- 2.24 and HE: 10.60 +/- 3.64 ms(2) . Hz (-1), p < 0.05). In relative terms, ME showed similar results in both LFn (LF/LF+HF) and HFn (HF/LF+HF) whereas HE showed a large prevalence of HFn energy compared to LFn (p < 0.001). The difference in LF/HF ratio between the two exercise conditions was significant (1.14 +/- 0.92 vs. 0.09 +/- 0.12, p < 0.001). Exercise repetition induced a significant increase in heart rate between the beginning and the end of the interval training session (207 +/- 10 beats . min (-1) vs. 212 +/- 9 beats . min (-1), p < 0.001) whereas LF energy decreases (1.54 +/- 1.65 vs. 0.32 +/- 0.24 ms(2) . Hz (-1), p < 0.01) and HF energy remained constant (10.79 +/- 4.10 vs. 10.40 +/- 3.35 ms(2) . Hz (-1), NS). This study confirmed the results observed in humans during heavy exercise conditions with a large prevalence of HF in contrast to LF, this prevalence increasing with exercise repetitions. The observed decrease in LF/HF ratio could provide an index of hyperpnea in horses during interval training.     

Effect of dietary fat on serum and intramyocellular lipids and running performance

PURPOSE: This study evaluated whether lowering IMCL stores via 3-d consumption of very-low-fat (LFAT) diet impairs endurance performance relative to a moderate-fat diet (MFAT), and whether such a diet unfavorably alters lipid profiles. METHODS: Twenty-one male and female endurance-trained runners followed a controlled diet and training regimen for 3 d prior to consuming either a LFAT (10% fat) or MFAT (35% fat) isoenergetic diet for another 3 d in random crossover fashion. On day 7, runners followed a glycogen normalization protocol (to equalize glycogen stores) and then underwent performance testing (90-min preload run at 62 +/- 1% VO2max followed by a 10-km time trial) on the morning of day 8. Muscle biopsies obtained from vastus lateralis before and after performance testing were analyzed for IMCL (via electron microscopy) and glycogen content (via enzymatic methodology). RESULTS: Despite approximately 30% lower IMCL (0.220 +/- 0.032% LFAT, 0.316 +/- 0.049% MFAT; P = 0.045) and approximately 22% higher muscle glycogen stores at the start of performance testing (P = 0.10), 10-km performance time was not significantly different following the two diet treatments (43.5 +/- 1.4 min LFAT vs 43.7 +/- 1.2 min MFAT). However, LFAT produced less favorable lipid profiles (P < 0.01) by increasing fasting triglycerides (baseline = 84.9 +/- 8.6; LFAT = 118.7 +/- 10.0 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.42 +/- 0.13:1; LFAT = 3.75 +/- 0.20:1), whereas MFAT lowered triglycerides (baseline = 97.5 +/- 12.2; MFAT = 70.9 +/- 7.1 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.47 +/- 0.18:1; MFAT = 3.33 +/- 0.14:1). CONCLUSION: The results suggest that reducing IMCL via 3-d consumption of a LFAT diet does not impair running performance lasting a little over 2 h (compared with 3-d consumption of a MFAT diet plus 1-d glycogen normalization), but that even short-term consumption of a LFAT diet may unfavorably alter serum lipids, even in healthy, endurance-trained runners.     

The effects of swimming exercise on high-fat-diet-induced steatohepatitis

AIM: The aim of this study was to assess the effects of swimming exercise on high-fat (HF) diet-induced steatohepatitis. METHODS: Two groups of rats were fed a HF diet (35%; kcal) for 12 weeks, with one group remained sedentary (HF-Sed) and the other group swam (HF-Tr) during this entire period. A third group was fed a standard diet and remained sedentary for 12 weeks (SD-Sed). Swimming exercise (5 days/week) was initiated at the same time as the HF diet and was progressively increased, until it reached 90 min after 4 weeks. RESULTS: At the end of the 12-week period, HF-Sed rats exhibited higher body weight (means +/- standard error [SE]: 492+/-40 vs 432+/-21 g; P<0.05), liver weight (16.21+/-2.23 vs 9.92+/-1.14 g; P<0.05), serum alanine aminotransferase (73.62+/-36.11 vs 27.16+/-4.62 U/L; P<0.05), aspartic aminotransferase (AST; 198.87+/-120.16 vs 120.16+/-19.09 U/L; P<0.05), nonesterified fatty acids (NEFA; 897.48+/-133.62 vs 437.5 micromol/L; P<0.05), triglyceride (0.92+/-0.1 vs 0.56+/-0.04 mmol/L; P<0.05), tumor necrosis factor (TNF)-a (21.74+/-2.93 vs 16.57+/-3.53 pg/mL; P < 0.05) as well as liver malondialdehyde (MDA; 5.3+/-1.45 vs 3.48+/-0.94 nmol/mg protein; P<0.05) and NEFA (305.47+/-69.23 vs 204.56+/-64.26 micromol/mg protein; P<0.05) than SD-Sed rats. All HF-Sed rats developed moderate to severe hepatic steatosis and steatohepatitis according to liver histological findings. Compared with HF-Sed, HF-Tr rats' hepatopathological manifestations of steatosis and inflammation were much attenuated, and their serum and liver parameters were all lower with the exception of serum AST. CONCLUSION: It was concluded that swimming exercise might reduce the incidence of HF-diet-induced steatohepatitis.     

Effect of repeated caffeine ingestion on repeated exhaustive exercise endurance

PURPOSE: The purpose of this study was to examine the effect of repeated doses of caffeine on repeated exercise endurance.METHODS Nine male caffeine users performed exercise rides (ER) to exhaustion at 80% VO(2max) after ingesting a placebo, 5 mg x kg-1 of caffeine, or 2.5 mg x kg-1 of caffeine 1 h before the ER. Two ER were performed weekly on the same day once in the morning (AM) and 5 h later in the afternoon (PM). There were four treatments containing either caffeine or placebo, i.e., trial A representing 5-mg x kg-1 caffeine in the AM and 2.5-mg x kg-1 caffeine in the PM; trial B, which was placebo in both AM and PM; trial C representing 5-mg x kg-1 caffeine in the AM and placebo in the PM; and trial D representing a placebo in the AM and 5-mg x kg-1 caffeine in the PM. The order of the treatment trials was double blind and randomized. RESULTS: Caffeine ingestion significantly increased exercise time to exhaustion in the AM (trial A 24.9 +/- 10.2 min and trial C 21.8 +/- 4.9 vs trial B 18.0 +/- 6.4 min and D 17.7 +/- 4.3 min). This effect was maintained in the PM and greater than placebo (B 18.3 +/- 4.8 min) regardless of whether redosing (trial A 21.5 +/- 8.6 min) or placebo (trial C 21.0 +/- 6.8) followed the initial morning dose. Caffeine dosing in the PM (trial D 22.4 +/- 7.2 min) also increased ER after placebo trial D in the AM. CONCLUSIONS: It was concluded that redosing with caffeine after exhaustive exercise in the AM was not necessary to maintain the ergogenic effect of the drug during subsequent exercise 6 h later.     

Heart rate variability during recovery from a Wingate test in adolescent males

PURPOSE: To evaluate the effect of maturity status on the autonomic nervous system at rest and recovery after short-term, high-intensity exercise in adolescents. METHODS: A biological maturity age was estimated in 27 males by calculating the years from peak height velocity (PHV) using a multiple regression equation. Subjects were divided into two groups: pre-PHV (years from PHV < 0.49), N = 14, mean age = 12.29 +/- 0.91 yr; post-PHV (years from PHV > 0.5, N = 13, mean age = 15.12 +/-0.76 yr). HR variability was used to evaluate autonomic function. ECG tracings were collected during 5 min at rest and recovery after a Wingate test and were analyzed in the frequency domain (low-frequency (LF), high-frequency (HF), LF/HF, total power (TP)). Data are presented as natural logarithms (LN). RESULTS: Changes in HR from HR(peak) during exercise to HR measured at minute 4 after exercise ([DELTA]HR4) were significantly greater in the pre-PHV group (84.31 +/-17.58 bpm) compared with the post-PHV group (69.42 +/-17.63 bpm). There were no significant differences in resting HR variability between pre- and post-PHV groups (P > 0.05). Significant group x time interactions were found for LF(LN) (ms(2)) and TP(LN) (ms(2)) measured during recovery (P < 0.05). Post hoc tests showed that the pre-PHV group had significantly higher postexercise LF(LN) (5.02 +/- 0.97 vs 4.19 +/- 0.79) and TP(LN) (6.36 +/- 1.02 vs 5.62 +/- 0.65) compared with the post-PHV group. When postexercise LF(LN) (ms(2)) was normalized for TP(LN) (ms(2)), there were no significant differences between groups (P > 0.05). CONCLUSION: The pre-PHV group had higher total HR variability than the post-PHV group after a Wingate test, suggesting that maturity status significantly affects total HR variability during recovery after high-intensity exercise.     

Normalization of diastolic dysfunction in type 2 diabetics after exercise training

PURPOSE: The purpose of this study was to evaluate the impact of aerobic exercise training on left ventricular diastolic dysfunction (LVDD) and exercise capacity in subjects with type 2 diabetes. METHODS: Twenty-three sedentary subjects with well-controlled type 2 diabetes, free of coronary disease and having different degrees of LVDD, participated in the study. Subjects were treated with oral hypoglycemic agents and/or diet. Eleven subjects (EX) (age: 58 +/- 5 yr; mean +/- SD) underwent a 3-month aerobic exercise training program using a cycle ergometer, whereas a control group (CONT) of 12 subjects (57 +/- 6 yr) maintained their activities of daily living. Exercise capacity and LVDD, using echocardiography, were evaluated before and after the 3-month exercise program. RESULTS: At baseline, anthropometric data were similar between the groups, except for body mass index (BMI), which was higher in CONT (31 +/- 3 vs 28+/- 3 kg x m(-2); P < 0.05). There were no significant differences in glycemic control (HbA1c: 6.4 +/- 1.2 vs 5.8 +/- 1.3%; P = 0.2) or maximal oxygen uptake (26.7 +/- 5.9 vs 28.6 +/- 3.9 mL x kg(-1) x min(-1); P = 0.4) between groups. Normalization of LVDD was observed in 5 of 11 EX subjects, (P < 0.0001) of whom four had grade 1 LVDD before exercise training. No change in diastolic function was observed in the CONT group. After exercise training, maximal oxygen uptake increased in the EX group (28.6 +/- 3.9 vs 32.7 +/- 5.7 mL x kg(-1) x min(-1); P < 0.05), whereas there was no change in the CONT group (26.7 +/- 5.9 vs 27.3 +/- 6.2 mL x kg(-1) x min(-1); P = 0.58). In both groups, there was no significant change in BMI. CONCLUSIONS: Along with an improvement in exercise capacity, aerobic exercise training has the potential to reverse LVDD in patients with well-controlled, uncomplicated type 2 diabetes.     

Exercise attenuates the weight-loss-induced reduction in muscle mass in frail obese older adults

PURPOSE: To evaluate the effect of adding exercise to a hypocaloric diet on changes in appendicular lean mass and strength in frail obese older adults undergoing voluntary weight loss. METHODS: Thirty frail older (age, 70 +/- 5 yr) obese (body mass index, 37 +/- 5 kg.m) adults were randomly assigned to 6 months of diet/behavioral therapy (diet group, n = 15) or diet or behavioral therapy plus exercise that incorporated progressive resistance training (PRT; diet + exercise group; n = 15). Body composition was assessed using dual-energy x-ray absorptiometry, and muscle strength was assessed using one-repetition maximum. The volume of upper extremity (UE) and lower extremity (LE) exercise training was determined by multiplying the average number of repetitions performed by the average weight lifted during the first three exercise sessions and during the last three exercise sessions of the study. RESULTS: The diet and the diet + exercise groups had similar (P > 0.05) decreases in weight (10.7 +/- 4.5 vs 9.7 +/- 4.0 kg) and fat mass (6.8 +/- 3.7 vs 7.7 +/- 2.9 kg). However, the diet + exercise group lost less fat-free mass (FFM; 1.8 +/- 1.5 vs 3.5 +/- 2.1 kg), LE lean mass (0.9 +/- 0.8 vs 2.0 +/- 0.9 kg), and UE lean mass (0.1 +/- 0.2 vs 0.2 +/- 0.2 kg) than the diet group (P < 0.05). The diet + exercise group had greater increases in percent of weight as FFM (FFM / weight x 100) than the diet group (7.9 +/- 3.3 vs 5.4 +/- 3.7%; P < 0.05). Despite lean mass losses, the diet + exercise group increased UE and LE strength in response to exercise (17-43%), whereas the diet group maintained strength. The volume of UE and LE exercises correlated with the amount of UE and LE lean mass (r = 0.64-0.84; P < 0.05). CONCLUSION: Exercise added to diet reduces muscle mass loss during voluntary weight loss and increases muscle strength in frail obese older adults. Regular exercise that incorporates PRT should be used to attenuate muscle mass loss in frail obese older adults on weight-loss therapy.     

Recovery of muscle glycogen concentrations in sled dogs during prolonged exercise

PURPOSE: To determine the depletion of muscle glycogen during five consecutive days of endurance exercise in Alaskan sled dogs consuming a high-fat, low-carbohydrate diet. METHODS: Forty-two fit Alaskan sled dogs were used in the study, of which six dogs served as nonexercising control animals. The remaining 36 dogs ran 160 km x d(-1) for up to 5 d while consuming a diet providing approximately 50% of calories as fat and 15% as carbohydrate. Muscle biopsies were performed on six randomly selected dogs before feeding and within 4 h after each 160-km run was completed. Muscle samples were prepared for analysis of glycogen content and myosin ATPase staining. Serum creatine kinase (CK) activity was measured once before exercise and after each 160-km run. RESULTS: Thirty-three of 36 dogs completed the runs. Muscle glycogen concentration was highest in sedentary dogs (340 +/- 102 mmol x kg(-1) dry weight), declined to 73 +/- 16 after 160 km and subsequently increased to similar levels between 320 and 800 km (320 km: 177 +/- 34; 800 km: 213 +/- 44). Postexercise serum CK activity was significantly elevated throughout the study. CONCLUSION: Skeletal muscle in Alaskan sled dogs has remarkable glyconeogenic ability as demonstrated by repletion to greater than 50% of resting muscle glycogen concentrations after the second of five consecutive 160-km runs even when fed a low-carbohydrate, high-fat diet. Whether this finding is attributable to rapid repletion of muscle glycogen during brief recovery periods versus progressive utilization of alternative substrates remains to be investigated.     

Aerobic influence on neuromuscular function and tolerance during passive hyperthermia

PURPOSE: To determine the role of aerobic fitness on central neuromuscular activation and maximal voluntary contractile force during hyperthermia. METHODS: Thirty-seven healthy males in three distinct groups based on aerobic fitness and training history were passively heated using a liquid conditioning garment in a hot (35 degrees C, 50% RH) environment with the intention of testing neuromuscular function with whole-body hyperthermia. Of these initial participants, 11 of the 13 highly fit (HF; VO2max = 71.2 +/- 5.9 mL x kg(-1) x min(-1), body fat = 5.6 +/- 1.9%), 11 of the 13 moderately fit (MF; 57.2 +/- 4.2 mL x kg(-1) x min(-1), 11 +/- 3.4%), and 4 of the 11 lower-fit (LF; 49.6 +/- 1.1 mL x kg(-1) x min(-1), 19.4 +/- 2.6%) individuals tolerated heating to 39.0 degrees C, with the remainder terminating the experimental protocol early. Maximal force output and voluntary activation were examined during a 10-s maximal isometric knee extension. RESULTS: Passive heating attenuated force production (-61.7 +/- 69.6 N change from initial values) and decreased voluntary activation (8.6 (12.6), 18.1 (12.4), and 6.1 (3.1)% for HF, MF, and LF training groups, respectively). Cardiovascular strain moderately increased to 60 +/- 14% (P < 0.001), whereas HF and MF had significantly higher MAP than LF at the end of heating (98 +/- 15, 99 +/- 7, and 79 +/- 5 mm Hg for HF, MF, and LF, respectively; P < 0.05). However, the ability to tolerate passive heating to 39.0 degrees C (and above) differed between the HF and MF compared with LF, despite no difference in their psychophysical rankings of thermal sensations and/or (dis)comfort. CONCLUSION: Low aerobic fitness and activity level are associated with a decreased tolerance to passive hyperthermia. However, at high body temperatures, maximum force production and voluntary activation were impaired to an equal level regardless of training status.     

Lifelong physical training prevents the age-related impairment of heart rate variability and exercise capacity in elderly people

AIM: Aging is associated with a reduction on heart rate variability (HRV) and working capacity. Aim of this study was to evaluate in a group of elite master athletes the effect of a lifelong history of endurance running on HRV and exercise working capacity. METHODS: Twenty athletes (males, age 68.5+/-4.5 years) who practiced endurance running for at least 40 years, and 20 age-sex-matched control subjects with sedentary lifestyle were studied. All the participants underwent a maximal stepwise electrocardiogram (ECG) on effort (work-rate increments of 25 Watts every 2 min) and a 24-hour ECG monitoring. RESULTS: All the time domain measures of HRV and the LF and HF powers were significantly higher in elderly athletes than in sedentary subjects (P<0.001), while the LF/HF ratio was comparable between the 2 groups. Athletes exhibited significantly higher workload than controls (1610+/-489 vs 687+/-236 W, P<0.0001). Both the groups achieved, at maximum workload, similar heart rate (142+/-10 vs 138+/-18 bpm, ns), systolic blood pressure (226+/-18 vs 220+/-16 mmHg, ns), and rate-pressure product (32,596+/-2952 vs 30,838+/-3675, ns). Maximum work-rate attained in athletes was 225 W. By contrast, none of the controls reached a work-rate higher than 150 W. In the whole group we also showed a positive correlation between the time domain HRV parameter SDNN and maximum workload (r=0.58, P<0.001). CONCLUSION: Long-term endurance training induces in elderly subjects an increased HRV and a higher exercise working capacity, which are well-established predictors of cardiovascular and overall mortality.     

Physiological and thermal responses of males with varying body compositions during immersion in moderately cold water.

The effect of body composition on the thermal and metabolic responses of 24 male volunteers (20 to 35 years) was examined during 90 min of moderately cold (18, 22, or 26 degrees C) water immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to body fat (high fat (HF) = 18-22%, n = 12; Low fat (LF) = 8-12%, n = 12) and randomly assigned to one of three water temperatures. Rectal temperature (degree C) after 90 min of immersion did not differ in LF and HF at 18 degrees C (35.9 vs. 36.2), 22 degrees C (36.0 vs. 36.0), and 26 degrees C (36.0 vs. 36.3). Oxygen uptake (VO2, ml-kg-1.min-1) was greater in LF than in HF in all water temperatures. Oxygen uptake at 90 min was greater for LF than HF in 18 degrees C (11.48 vs. 9.19), 22 degrees C (9.79 vs. 4.70), and 26 degrees C (6.21 vs. 5.44). Mean skin temperature in LF and HF approached water temperature within the first 5 min. Despite the thermal strain of cold water immersion, the LF subjects were able to maintain a similar Tre compared to the HF due to a significantly greater shivering thermogenesis.     

Effects of short-term fat adaptation on metabolism and performance of prolonged exercise

The concept of manipulating an individuals habitual diet before an exercise bout in an attempt to modify patterns of fuel substrate utilization and enhance subsequent exercise capacity is not new. Modern studies have focused on nutritional and training strategies aimed to optimize endogenous carbohydrate (CHO) stores while simultaneously maximizing the capacity for fat oxidation during continuous, submaximal (60-70% of maximal O(2) uptake [(.)VO(2max)] exercise. Such "nutritional periodization" typically encompasses 5-6 d of a high-fat diet (60-70% E) followed by 1-2 d of high-CHO intake (70-80% E; CHO restoration). Despite the brevity of the adaptation period, ingestion of a high-fat diet by endurance-trained athletes results in substantially higher rates of fat oxidation and concomitant muscle glycogen sparing during submaximal exercise compared with an isoenergetic high-CHO diet. Higher rates of fat oxidation during exercise persist even under conditions in which CHO availability is increased, either by having athletes consume a high-CHO meal before exercise and/or ingest glucose solutions during exercise. Yet, despite marked changes in the patterns of fuel utilization that favor fat oxidation, fat-adaptation/CHO restoration strategies do not provide clear benefits to the performance of prolonged endurance exercise.     

Physiological responses to weight-loss intervention in inactive obese African-American and Caucasian women

BACKGROUND: The physiological responses of inactive obese premenopausal African-American and Caucasian women to the identical exercise training and behavior modification program were compared. METHODS: Inactive obese (96.1+/- 2.9 kg, BMI=34.8 +/- 0.7 kg/m2, % body fat=46.0 +/- 0.8; mean +/- SEM) premenopausal (36 +/- 2 yrs) African-American (n=10) and Caucasian (n=19) women were included. Resting metabolic rate (RMR), respiratory exchange ratio (RER), and maximal aerobic power (VO2max) were measured by indirect calorimetry, and body composition by plethysmography. Resting and maximal heart rates, blood glucose and lipids, and blood pressure were also measured. Treatment consisted of a 13-week diet and exercise behavior modification program. Group mean comparisons were made with a Student's "t"-test or an ANCOVA, which controlled for individual differences in body mass and lean body mass (LBM). Significance was set at p<0.05. RESULTS: Initially, the groups were not significantly different in height, mass, BMI, age, % body fat, fat mass, LBM, girth measurements, RMR, RER, VO2max, blood pressure, or cholesterol profile. The number of weeks completed, number of exercise sessions completed, total minutes of exercise for the entire intervention, average minutes of daily exercise, and total estimated exercise energy expenditure were all similar between groups. Furthermore, both groups reported similar dietary compliance. Both groups reduced body mass, BMI, LBM, girth measurements, and increased VO2max (mlO2 x kg-1 x min-1) significantly and similarly. CONCLUSIONS: African-American and Caucasian women respond the same physiologically to weight loss intervention. The higher prevalence in obesity for African-American women is not due to a different physiological response to diet and exercise.