Todd A. Hagobian

Physical Activity and Hormonal Regulation of Appetite: Sex Differences and Weight Control

Todd A. Hagobian et al. — Wed, 17 Feb 2010 10:53:53 PST

Physical activity is an important contributor to regulation of energy balance and body composition. In this article, we separate the impact of exercise from the confounding influence of energy imbalance and highlight sex differences in hormonal and appetite responses to physical activity. The evolving story may influence our thinking regarding the use of physical activity to manage body composition.

Effects of Heat Removal Through the Hand on Metabolism and Performance During Cycling Exercise in the Heat

Andrew R. Hsu et al. — Wed, 03 Feb 2010 09:43:35 PST

OBJECTIVE: This two-part study tested the hypotheses that the use of a new cooling device, purported to extract heat from the body core through the palm of the hand, would (a) attenuate core temperature rise during submaximal exercise in the heat, thereby suppressing exercise-associated metabolic changes, and (b) facilitate a higher sustained workload, thus shortening the completion time of a time-trial performance test. METHODS: In Study 1, 8 male triathletes (age 27.9 ± 2.0 yrs, mass 77.2 ± 3.1 kg, VO₂peak 59.0 ± 4.1 ml x min^-1 x kg^-1) cycled for 1 hr at the same absolute workload (~60% VO₂peak) in a heated room (31.9 ± 0.1 °C, 24 ± 1% humidity) on two occasions counterbalanced for cooling (C) or noncooling (NC). In Study 2, 8 similar subjects (age 26.9 ± 2.0 yrs, mass 75.2 ± 3.7 kg, VO₂peak 54.1 ± 3.1 ml x min^-1 x kg^-1) performed two 30-km cycling time-trial performance tests under the same conditions (C_T, NC_T). RESULTS: In Study 1, cooling attenuated the rise in tympanic temperature (T_TY) (1.2 ± 0.2 vs. 1.8 ± 0.2 °C; p < 0.01) and lowered mean oxygen consumption (VO₂, 2.4 ± 0.1 vs. 2.7 ± 0.1 L x min^-1; p < 0.05) and blood lactate (1.7 ± 0.2 vs. 2.2 ± 0.2 mmol x L^-1; p < 0.01) during exercise. There were no significant differences in respiratory exchange ratio (RER), blood glucose, heart rate (HR), face temperature (T_F), or back temperature (T_B) between NC and C. In Study 2, time to complete 30 km was 6 ± 1% less with cooling than without cooling (60.9 ± 2.0 vs. 64.9 ± 2.6 min; p < 0.01). During the last 20% of C_T, subjects sustained a workload that was 14 ± 5% (p = 0.06) higher than NC_T at the same T_TY and HR. CONCLUSIONS: Heat extraction through the hand during cycle ergometer exercise in the heat can (a) lower T_TY, lactate concentration, and VO₂ during a submaximal set-workload test and (b) reduce the time it takes to complete a 30-km time-trial test.

Cytokine Response at High Altitude: Effects of Exercise and Antioxidants at 4300 m

Todd A. Hagobian et al. — Fri, 29 Jan 2010 13:27:34 PST

Purpose: This study tested the hypothesis that antioxidant supplementation would attenuate plasma cytokine (IL-6, tumor necrosis factor (TNF)-α), and C-reactive protein (CRP) concentrations at rest and in response to exercise at 4300-m elevation.
Methods: A total of 17 recreationally trained men were matched and assigned to an antioxidant (N = 9) or placebo (N = 8) group in a double-blinded fashion. At sea level (SL), energy expenditure was controlled and subjects were weight stable. Then, 3 wk before and throughout high altitude (HA), an antioxidant supplement (10,000 IU β-carotene, 200 IU α-tocopherol acetate, 250 mg ascorbic acid, 50 2g selenium, 15 mg zinc) or placebo was given twice daily. At HA, energy expenditure increased approximately 750 kcald^-1 and energy intake decreased approximately 550 kcald^-1, resulting in a caloric deficit of approximately 1200–1500 kcald^-1. At SL and HA day 1 (HA1) and day HA13, subjects exercised at 55% of VO_2peak until they expended approximately 1500 kcal. Blood samples were taken at rest, end of exercise, and 2, 4, and 20 h after exercise.
Results: No differences were seen between groups in plasma IL-6, CRP, or TNF-! at rest or in response to exercise. For both groups, plasma IL-6 concentration was significantly higher at the end of exercise, 2, 4, and 20 h after exercise at HA1 compared with SL and HA13. Plasma CRP concentration was significantly elevated 20 h postexercise for both groups on HA1 compared to SL and HA13. TNF-α did not differ at rest or in response to exercise.
Conclusion: Plasma IL-6 and CRP concentrations were elevated following exercise at high altitude on day 1, and antioxidant supplementation did not attenuate the rise in plasma IL-6 and CRP concentrations associated with hypoxia, exercise, and caloric deficit.

Impact of Metformin on Peak Aerobic Capacity

Barry Braun et al. — Fri, 29 Jan 2010 13:27:33 PST

Individually, exercise and the drug metformin have been shown to prevent or delay type 2 diabetes. Metformin mildly inhibits complex I of the electron transport system and may impact aerobic capacity in people exercising while taking metformin. The purpose of the study was to evaluate the effects of metformin on maximal aerobic capacity in healthy individuals without mitochondrial dysfunction. Seventeen healthy, normal-weight men (n=11) and women (n=6) participated in a double-blind, placebo-controlled, cross-over design. Peak aerobic capacity was measured twice using a continuous, incrementally graded protocol; once after 7-9 d of metformin (final dose=2000 mg/d) and once with placebo, with 1 week between tests. The order of the conditions was counterbalanced. Peak oxygen uptake (VO2 peak), heart rate (HR), ventilation (VE), respiratory exchange ratio (RER), rating of perceived exertion (RPE), and test duration were compared across conditions using paired t tests with the R statistical program. VO2 peak (-2.7%), peak heart rate (-2.0%), peak ventilation (-6.2%), peak RER (-3.0%), and exercise duration (-4.1%) were all reduced slightly, but significantly, with metformin (all p<0.05). There was no effect of metformin on RPE or ventilatory breakpoint. Correlations between the decrement in VO2 peak and any of the other outcome variables were weak (r2<0.20) and not significant. Short-term treatment with metformin has statistically significant, but physiologically subtle, effects that reduce key outcomes related to maximal exercise capacity. Whether this small but consistent effect is manifested in people with insulin resistance or diabetes who already have some degree of mitochondrial dysfunction remains to be determined.

Foot Cooling Reduces Exercise-Induced Hyperthermia in Men with Spinal Cord Injury

Todd A. Hagobian et al. — Fri, 29 Jan 2010 13:27:33 PST

The number of individuals with spinal cord injury (SCI) participating in sports at recreational and elite levels is on the rise. However, loss of autonomic nervous system function below the lesion can compromise thermoregulatory capacity and increase the risk of heat stress relative to able-bodied (AB) individuals.
Purpose: To test the hypotheses that exercise in a heated environment would increase tympanic temperature (TTY) more in individuals with SCI than AB individuals, and that foot cooling using a new device would attenuate the rise in TTY during exercise in both groups.
Methods: Six subjects with SCI (lesions C5–T5) and six AB controls were tested in a heated environment (means ± SEM, temperature ± 31.8 ± 0.2°C, humidity ± 26 ± 1%) for 45 min at 66% ± 5 of arm cranking V˙ O2peak and 30 min of recovery on two separate occasions with foot cooling (FC) or no foot cooling (NC) in randomized order.
Results: During exercise and recovery in both trials, SCI TTY was elevated above baseline (P < 0.001) but more so in the NC versus FC trial (1.6 ± 0.2°C vs 1.0 ± 0.2°C, respectively, P < 0.005). Within the AB group, TTY was elevated above baseline for both trials (P < 0.001) with peak increases of 0.5 ± 0.2°C and 0.3 ± 0.2°C for NC and FC, respectively. TTY, face, and back temperature were higher in both SCI trials compared with AB trials (P < 0.05). Heart rate during exercise and recovery was lower in the SCI FC versus SCI NC (P < 0.05).
Conclusion: These results suggest that extraction of heat through the foot may provide an effective way to manipulate tympanic temperature in individuals with SCI, especially during exercise in the heat.

Changes in Ventilatory Threshold at High Altitude: Effect of Antioxidants

Andrew W. Subudi et al. — Fri, 29 Jan 2010 13:27:32 PST

Purpose: To investigate the effects of prolonged hypoxia and antioxidant supplementation on ventilatory threshold (VT) during high-altitude (HA) exposure (4300 m).
Methods: Sixteen physically fit males (25 ± 5 yr; 77.8 ± 8.5 kg) performed an incremental test to maximal exertion on a cycle ergometer at sea level (SL). Subjects were then matched on VO2peak, ventilatory chemosensitivity, and body mass and assigned to either a placebo (PL) or antioxidant (AO) supplement group in a randomized, double-blind manner. PL or AO (12 mg of β-carotene, 180 mg of α-tocopherol acetate, 500 mg of ascorbic acid, 100 μg of selenium, and 30 mg of zinc daily) were taken 21 d prior to and for 14 d at HA. During HA, subjects participated in an exercise program designed to achieve an energy deficit of approximately 1400 kcald^-1. VT was reassessed on the second and ninth days at HA (HA2, HA9).
Results: Peak power output (W_2peak) and VO_2peak decreased (28%) in both groups upon acute altitude exposure (HA2) and were unchanged with acclimatization and exercise (HA9). Power output at VT (W_VT) decreased from SL to HA2 by 41% in PL, but only 32% in AO (P < 0.05). W_VT increased in PL only during acclimatization (P < 0.05) and matched AO at HA9. Similar results were found when VT was expressed in terms of % W_peak and % VO_2peak.
Conclusions: VT decreases upon acute HA exposure but improves with acclimatization. Prior AO supplementation improves VT upon acute, but not chronic altitude exposure.

Interactions between energy surplus and short-term exercise on glucose and insulin responses in healthy people with induced, mild insulin insensitivity

Todd A. Hagobian et al. — Fri, 29 Jan 2010 13:27:31 PST

Short-term exercise can enhance insulin action, but the effect may be negated by the opposing action of energy surplus. The purpose of this investigation was to test the hypothesis that a single exercise bout would increase insulin action, even when opposed by a concurrent energy surplus. After 2 days in energy balance without exercise, baseline glucose and insulin areas under the curve and the insulin sensitivity index (C-ISI) were measured during an oral glucose tolerance test in 9 healthy, habitually active subjects (6 males, 3 females). A state of relative insulin insensitivity was then induced by systematic overfeeding (OF) to generate a daily energy surplus of 768 ± 203 kcal/d for 3 days, and the oral glucose tolerance test was repeated. In the following 24 hours, the OF was increased ∼2-fold (+6284 ± 1669 kJ/d) and subjects performed a single bout of exercise (expenditure = 3063 ± 803 kJ) to maintain the same energy surplus (+3125 ± 933 kJ/d; OF and exercise) as OF. After OF, fasting insulin tended to be higher (+36%, P = .099), insulin AUC rose by 38% (P = .002), and C-ISI declined from 6.6 ± 3.1 to 4.6 ± 1.8 (P = .007) compared with baseline. After OF and exercise, fasting insulin remained elevated (+43% compared with baseline; P = .043) and C-ISI rose only slightly (4.6 ± 1.8 to 5.2 ± 2.3; P = .058), but insulin AUC declined by 20% (P = .048) compared with OF. A single exercise bout, opposed by a concurrent energy surplus, decreased the insulin response to a glucose challenge, but only partially restored the insulin AUC to baseline and had no impact on C-ISI or fasting insulin concentrations.

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

Todd A. Hagobian et al. — Wed, 27 Jan 2010 12:19:40 PST

Energy surplus raises circulating concentrations of leptin and insulin while lowering plasma ghrelin. Exercise has the opposite effects. The purpose of this study was to determine whether exercise counters the hormonal effects of energy surplus independent of changes in energy balance. To do that, we assessed plasma concentrations of leptin, insulin, and ghrelin at baseline, after overfeeding, and after overfeeding plus exercise. Baseline (B) leptin and insulin concentrations and ghrelin area under the curve were measured during an oral glucose challenge in 9 healthy, active subjects (6 male, 3 female) after 2 days in energy balance without exercise. Measurements were repeated after subjects were overfed by +3213 ± 849 kJ/d for 3 more sedentary days (OF). In the third condition, the same net energy surplus (+3125 ± 933 kJ/d) was generated for 24 hours by doubling the overfeeding (+6284 ± 1669 kJ/d) and countering it with a bout of exercise (expenditure = 3063 ± 803 kJ); and measurements were made the next day (OF + EX). Compared with B, leptin went up (5.8 ± 8.2 to 7.6 ± 10.6 ng/mL) after OF, but was not significantly higher after OF + EX (7.1 ± 10.2 ng/mL). Compared with B, insulin was +36% and +43% higher after OF and OF + EX, respectively. In contrast, ghrelin area under the curve did not change after OF but was significantly lower (−14%) than B or OF after OF + EX (indicating greater suppression). These data suggest that the effect of short-term exercise on fasting leptin and insulin depends on energy balance but the ghrelin response may be partially mediated by effects of exercise independent of energy balance.