George J. Holland

Chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport

Leptin, the product of the ob gene, has been shown to reduce fat mass, food intake, hyperglycemia, and hyperinsulinemia and to increase whole-body glucose disposal. However, it is unknown if leptin improves insulin action in skeletal muscle. Therefore, the purpose of this investigation was to determine if chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport. Sixty-nine female Sprague-Dawley rats (240 to 250 g) were randomly assigned to one of three groups: (1) control, (2) pair-fed, and (3) leptin. All animals were subcutaneously implanted with miniosmotic pumps that delivered 0.5 mg leptin/kg/d to the leptin animals and vehicle to the control and pair-fed animals for 14 days. Following this 14-day period, all animals were subjected to hindlimb perfusion to determine the rates of skeletal muscle glucose uptake and 3-O-methyl-D-glucose (3-MG) transport under basal, submaximal (500 microU/mL), and maximal (10,000 microU/mL) insulin concentrations. Chronic leptin treatment significantly increased (P < .05) the rate of glucose uptake across the hindlimb by 27%, 32%, and 47% under basal, submaximal, and maximal insulin, respectively, compared with the control and pair-fed condition. However, when the submaximal rate of glucose uptake was expressed as a percentage of maximal insulin-stimulated glucose uptake, no differences existed among the groups, indicating that leptin treatment does not increase insulin sensitivity. Rates of 3-MG transport in the soleus, plantaris, and white and red portions of the gastrocnemius (WG and RG) were significantly increased (P < .05) in leptin animals under all perfusion conditions. 3-MG transport was not different between control and pair-fed animals. Collectively, these findings suggest that improvements in insulin-stimulated skeletal muscle glucose uptake and transport following chronic leptin treatment result from increased insulin responsiveness.

Effects of stairclimbing on VO2max and quadriceps strength in middle-aged females

The purpose of this study was to determine the effect of 12 wk of stairclimbing with and without an external load on aerobic capacity and quadriceps strength of sedentary (initial VO2max 25.3 +/- 0.73 ml.kg-1.min-1) (mean +/- SEM) middle aged females (50-65 yr). Three groups, LOAD (stairclimbing with external load, N = 8), STAIR (no load, N = 9), and CONTROL (N = 7) were tested. By week 4, subjects warmed up 5 min on a cycle ergometer followed by 35 min on the stairclimber at 80-85% maximum heart rate (MHR) 4 d.wk-1. In week 6, the LOAD group carried an external load of 4% of body weight increasing to 8% for weeks 7-12. STAIR and LOAD group significantly increased (P < 0.01) VO2max by 11.1% and 9.6%, respectively. Isokinetic strength tests showed increased (P < 0.05) peak torque and total work for STAIR and LOAD at 120 and 180 degrees.s-1. For total work, a significant increase (P < 0.05) of 10.5% was observed at 60 degrees.s-1 for the LOAD group. The results indicate stairclimbing is an appropriate exercise for middle-aged females improving both aerobic capacity and strength following 12 wk of training.

Effect of run vs combined cycle/run training on VO2max and running performance.

The effects of 5 wk of equivalent intensity, 85-90% maximum heart rate (MHR), run-only (N = 6) vs cycle/run (N = 5) training were evaluated in moderately fit runners, mean VO2max of 55.2 ml.kg-1.min-1, 19-35 yr old, on maximal treadmill (TM) and cycle ergometer (CE) testing, 5000-m and 1609-m run performances, and submaximal measures while treadmill running. Subjects participated in either 4 d.wk-1 of run-only or alternating run and cycle training. Both groups significantly improved TM VO2max (P < 0.05), CE VO2peak (P < 0.01), and 5000-m (P < 0.01) and 1609-m (P < 0.05) run times with no significant differences between the groups. The TM VO2max pre/post values were 55.3 +/- 3.0 to 58.2 +/- 3.0 and 55.6 +/- 3.8 to 58.9 +/- 2.4 ml.kg-1.min-1 for the run group and cross-trained group, respectively. Posttraining submaximal treadmill running showed statistically significant pace increases of 18.7 (run) and 16.1 (cycle/run) m.min-1 with similar heart rate, blood lactate, and RQ values as pretraining. Results indicate that 5 wk of either mode of training can significantly improve aerobic capacity and run performance.

Effects of stair-climbing vs run training on treadmill and track running performance

Physically active college age women were evaluated to determine the effects of 9 wk of stair-climbing (Stairmaster Gauntlet) vs run training on 2414-m run time and treadmill measured aerobic capacity (VO2max) and submaximal physiological parameters. Subjects were randomly assigned to a stair-climbing (STAIR N = 11) (43.8 +/- 1.5 ml.kg-1.min-1) (mean +/- SEM) or run training (RUN N = 12) (44.2 +/- 1.8) group, training 4 d.wk-1 at 70-80% of maximum heart rate (MHR) for 30 min progressing to 85-90% MHR for 45 min. The STAIR group significantly increased (P < 0.01) their VO2max by 12% and decreased (P < 0.01) their 2414-m run time of 12.8 min by 8%. The RUN group increased (P < 0.01) their VO2max 16% and decreased run time (P < 0.01) 11% from 13.1 min. Submaximal treadmill runs at the same speed and grade demonstrated significant decreases in %VO2max and % MHR (P < 0.01) for both groups. The data support the use of stair-climbing exercise as an alternative mode to running with similar treadmill and running performance results subsequent to 9 wk of training.

Specificity effects of run versus cycle training on ventilatory threshold

SummaryThis study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Thv) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days·week−1 at 75–80% maximum heart rate (fc,max) for 45 min. Training intensity was later increased to 80–85% fcmax and interval training (90–95% fc,max) was incorporated 2 days·week−1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption (

A physiological comparison of forward vs reverse wheelchair ergometry

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Effect of running versus cycle training on cycle ergometer, treadmill, and running performance

O2max) on both TM and CE tests (P<0.01) with no significant differences between the groups. Significant Thv increases (P<0.05) were found on TM tests for RT (n=8) and CT (n=8) groups [mean (SD); 443 (438) and 373 (568) ml O2·min−1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Thv increase (P<0.01) for the CT group [566 (663) ml O2·min−1] with no change for the RT group. The Thv improvement noted for the RT group was significantly different (P< 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Thv for runners is dependent upon mode of training and testing, and there is an apparent dissociation of