A comparison of dual-energy X-ray absorptiometry, air displacement plethysmography and A-mode ultrasound to assess body composition in college-age adults.

BACKGROUND: There is currently a dearth of scientific literature exploring the agreement of A-mode ultrasound (US) body composition analysis with dual-energy X-ray absorptiometry (DXA) and air displacement plethysmography (ADP). OBJECTIVE: To investigate the agreement of US with DXA and ADP for estimating fat mass (FM) and fat-free mass (FFM). METHODS: College-age men (n = 33) and women (n = 41) volunteered to participate in this study. Participants were instructed to adhere to the following pretest protocol: refrain from food and drink 12 h prior to testing and wear tight fitting clothing. Body composition (BCA) was assessed using US, DXA and ADP in accordance with the respective manufacturer's guidelines. Two-way mixed-model AVOVA and Bland and Altman techniques were applied to explore agreement for FM and FFM among the three methods: US, ADP and DXA and by sex. RESULTS: There was no statistically significant effect by sex for either FM or FFM across all BCA comparisons (P = 0·504 and 0·510, respectively). US was not statistically different from ADP for FM and FFM (P ≈ 1·00). However, for FM and FFM, there were significant differences between DXA and both US and ADP (P≤0·001). The Bland and Altman analyses revealed large individual differences for all BCA. CONCLUSION: There was statistical agreement between US and ADP for FM and FFM but lack of agreement for US and ADP when compared to DXA. However, the large limits of agreement between methods warrant caution in generalizing these findings.

The effect of 10 days of heat acclimation on exercise performance in acute hypobaric hypoxia (4350 m).

To examine the effect ("cross-tolerance") of heat acclimation (HA) on exercise performance upon exposure to acute hypobaric hypoxia (4350 m). Eight male cyclists residing at 1600 m performed tests of maximal aerobic capacity (VO2max) at 1600 m and 4350 m, a 16 km time-trial at 4350 m, and a heat tolerance test at 1600 m before and after 10 d HA at 40°C, 20% RH. Resting blood samples were obtained pre-and post- HA to estimate changes in plasma volume (ΔPV). Successful HA was indicated by significantly lower exercise heart rate and rectal temperature on day 10 vs. day 1 of HA and during the heat tolerance tests. Heat acclimation caused a 1.9% ΔPV, however VO2max was not significantly different at 1600 m or 4350 m. Time-trial cycling performance improved 28 sec after HA (p = 0.07), suggesting a possible benefit for exercise performance at acute altitude and that cross-tolerance between these variables may exist in humans. These findings do not clearly support the use of HA to improve exercise capacity and performance upon acute hypobaric hypoxia, however they do indicate that HA is not detrimental to either exercise capacity or performance.

Muscle activation of the quadriceps and hamstrings during incremental running.

INTRODUCTION: The aim of this study was to determine the patterns of responses for the electromyographic (EMG) amplitude vs. oxygen uptake ( V̇O2 ) relationships from muscles of the quadriceps femoris and hamstrings during incremental treadmill running. METHODS: Twelve men volunteered to perform an incremental test to exhaustion while EMG signals were recorded from the vastus lateralis, vastus medialis, biceps femoris, and semitendinosus muscles. Polynomial regression analyses were used to determine the best model fit for the EMG amplitude vs. V̇O2 relationships. RESULTS: There were significant (P < 0.05) increases in EMG amplitude across V̇O2 for the vastus lateralis (quadratic, R = 0.995), vastus medialis (quadratic, R = 0.997), biceps femoris (cubic, R = 0.999), and semitendinosus (linear, R = 0.992) muscles as well as the hamstrings-to-quadriceps ratio (cubic, R = 0.999). CONCLUSION: These findings indicate that the patterns of responses for muscle activation vs. exercise intensity appear to be unique among muscles of the thigh.

Development of an Anaerobic Sprint Running Test Using a Nonmotorized Treadmill.

The purpose of this study was to determine the test-retest reliability of a newly developed anaerobic sprint running test (ASRT) on a nonmotorized treadmill (NMT). Twenty-six collegiate male athletes (21.2 ± 2.1 years; 181.3 ± 6.5 cm; 79.0 ± 9.3 kg) completed 3 trials of a 25-second maximal effort sprint on an NMT against a workload set to 18% of their individual body mass. Anaerobic power was determined by relative peak power output (PP) and anaerobic capacity was determined by relative mean power output (MP) during the test. Blood lactate (BLa) responses and fatigue index (FI) were also determined. Test-retest reliability was assessed by intraclass correlation coefficients (ICCs) and coefficients of variation (CV%). Results indicated no significant difference between the 3 trials for PP (T1 = 29.95 ± 6.51 W·kg(-1), T2 = 28.57 ± 5.55 W·kg(-1), T3 = 29.47 ± 5.94 W·kg(-1)), MP (T1 = 20.97 ± 3.64 W·kg(-1), T2 = 20.50 ± 3.46 W·kg(-1), T3 = 21.17 ± 3.79 W·kg(-1), and FI (T1 = 55 ± 8%, T2 = 51 ± 8%, T3 = 52 ± 9%). Reliability between the 3 trials for PP (ICC: r = 0.96, CV: 7%) and MP (ICC: r = 0.97, CV: 6%) was considered high. Reliability for FI exhibited an ICC of r = 0.83 (CV: 6%). Postsprint BLa values were not significantly different (p = 0.49) between the 3 trials. Test-retest reliability for postsprint BLa was found to be good (r = 0.68, CV = 8.8%). The results of the study indicate that the ASRT is reliable for assessing PP and MP in highly motivated subjects. In addition, anaerobic testing using the ASRT may be a more sport-specific test to assess anaerobic performance for many coaches and athletes.