Estimation of Percent Body Fat by Hydrostatic Weighing in High Schools

Concerns with fitness have increased interest in body composition and ideal body weight. Although anthropometric (e.g. skinfold) measurements can quickly determine general body composition, hydrostatic weighings are more accurate. While most exercise physiology laboratories on university campuses have a specialized tank for performing hydrostatic weighings, adequate stations can be set up in any swimming pool for a minimal initial cost. Several scientific concepts can be demonstrated during this exercise: measurement of lung volumes, determination of body density and calculation of percent body fat

Electromyographic Data Do Not Support a Progressive Recruitment of Muscle Fibers During Exercise Exhibiting a VO2 Slow Component

The origin of the slow component (SC) of oxygen uptake kinetics, presenting during exercise above the ventilatory threshold (VT), remains unclear. Possible physiologic mechanisms include a progressive recruitment of type II muscle fibers. The purpose of this study was to examine alterations in muscle activity through electromyography (EMG) and mean power frequency (MPF) analysis during heavy cycling exercise. Eight trained cyclists (mean±S.E.; age=30±3 years, height=177±4 cm, weight=73.8±6.5 kg, VO2max=4.33±0.28lmin−1) completed transitions from 20 W to a workload equaling 50% of the difference between VT and VO2max. VO2 was monitored using a breath-by-breath measurement system, and EMG data were gathered from surface electrodes placed on the gastrocnemius lateralis and vastus lateralis oblique. Breath-by-breath data were time aligned, averaged, interpolated to 1-s intervals, and modeled with non-linear regression. Mean power frequency (MPF) and RMS EMG values were calculated for each minute during the exercise bout. Additionally, MPF was determined using both isolated EMG bursts and complete pedal revolutions. All subjects exhibited a VO2 SC (mean amplitude=0.98±0.16lmin−1), yet no significant differences were observed during the exercise bout in MPF or RMS EMG data (p\u3e0.05) using either analysis technique. While it is possible that the sensitivity of EMG may be insufficient to identify changes in muscle activity theorized to affect the VO2 SC, the data indicated no relationship between MPF/EMG and the SC during heavy cycling

Is active sweating during heat acclimation required for improvements in peripheral sweat gland function?

We investigated whether the eccrine sweat glands must actively produce sweat during heat acclimation if they are to adapt and increase their capacity to sweat. Eight volunteers received intradermal injections of BOTOX, to prevent neural stimulation and sweat production of the sweat glands during heat acclimation, and saline injections as a control in the contralateral forearm. Subjects performed 90 min of moderate-intensity exercise in the heat (35°C, 40% relative humidity) on 10 consecutive days. Heat acclimation decreased end-exercise heart rate (156 ± 22 vs. 138 ± 17 beats/min; P = 0.0001) and rectal temperature (38.2 ± 0.3 vs. 37.9 ± 0.3°C; P = 0.0003) and increased whole body sweat rate (0.70 ± 0.29 vs. 1.06 ± 0.50 l/h; P = 0.030). During heat acclimation, there was no measurable sweating in the BOTOX-treated forearm, but the control forearm sweat rate during exercise increased 40% over the 10 days (P = 0.040). Peripheral sweat gland function was assessed using pilocarpine iontophoresis before and after heat acclimation. Before heat acclimation, the pilocarpine-induced sweat rate of the control and BOTOX-injected forearms did not differ (0.65 ± 0.20 vs. 0.66 ± 0.22 mg·cm−2·min−1). However, following heat acclimation, the pilocarpine-induced sweat rate in the control arm increased 18% to 0.77 ± 0.21 mg·cm−2·min−1 (P = 0.021) but decreased 52% to 0.32 ± 0.18 mg·cm−2·min−1 (P < 0.001) in the BOTOX-treated arm. Using complete chemodenervation of the sweat glands, coupled with direct cholinergic stimulation via pilocarpine iontophoresis, we demonstrated that sweat glands must be active during heat acclimation if they are to adapt and increase their capacity to sweat

Skeletal muscle fatigue precedes the slow component of oxygen uptake kinetics during exercise in humans

During constant work rate (CWR) exercise above the lactate threshold (LT), the exponential kinetics of oxygen uptake () are supplemented by a slow component () which reduces work efficiency. This has been hypothesised to result from ‘fatigue and recruitment’, where muscle fatigue during supra-LT exercise elicits recruitment of additional, but poorly efficient, fibres to maintain power production. To test this hypothesis we characterised changes in the power–velocity relationship during sub- and supra-LT cycle ergometry in concert with kinetics. Eight healthy participants completed a randomized series of 18 experiments consisting of: (1) a CWR phase of 3 or 8 min followed immediately by; (2) a 5 s maximal isokinetic effort to characterize peak power at 60, 90 and 120 rpm. CWR bouts were: 20 W (Con); 80% LT (Mod); 20%Δ (H); 60%Δ (VH); where Δ is the difference between the work rate at LT and . The was 238 ± 128 and 686 ± 194 ml min−1 during H and VH, with no discernible during Mod. Peak power in Con was 1025 ± 400, 1219 ± 167 and 1298 ± 233 W, at 60, 90 and 120 rpm, respectively, and was not different after Mod (P > 0.05). Velocity-specific peak power was significantly reduced (P < 0.05) by 3 min of H (−103 ± 46 W) and VH (−216 ± 60 W), with no further change by 8 min. The was correlated with the reduction in peak power (R2= 0.49; P < 0.05). These results suggest that muscle fatigue is requisite for the . However, the maintenance of velocity-specific peak power between 3 and 8 min suggests that progressive muscle recruitment is not obligatory. Rather, a reduction in mechanical efficiency in fatigued fibres is implicated