Vitamin D supplementation trial in infancy: body composition effects at 3 years of age in a prospective follow-up study from Montréal.

BACKGROUND: The impact of vitamin D status on body composition is not well understood. OBJECTIVES: Evaluate how vitamin D supplementation in infancy affects body composition at 3 years of age. METHODS: Double-blind randomized trial of 132, 1-month-old healthy, breastfed infants randomly assigned to receive oral vitamin D3 supplements of 400, 800, 1200 or 1600 IU d-1 for 11 months. In the present analysis, 87 (66%) returned at 3 years of age. Body composition was measured using dual-energy x-ray absorptiometry and plasma 25-hydroxyvitamin D [25(OH)D] concentrations by liquid chromatography tandem mass spectrometry. RESULTS: Anthropometry, body composition, diet, activity and demographics were similar across dosage groups at 3 years. Mean 25(OH)D concentration from 1 month to 3 years was higher (P < 0.001) in the 1200 IU group than 800 and 400 IU groups. Children with 25(OH)D concentrations above 75 nmol L-1 had lower fat mass (~450 g; P = 0.049). In multiple linear regression, mean 25(OH)D was associated with lean mass percent (ß = 0.06; CI: 0.00, 0.12; P = 0.042), fat mass (ß = -11.29; CI: -22.06, -0.52; P = 0.048) and body fat percent (ß = -0.06; CI: -0.12, -0.01; P = 0.045). CONCLUSIONS: Higher vitamin D status from infancy through to 3 years of age associates with leaner body composition.

Effects of whole-body vibration applied to lower extremity muscles during decline bench press exercise.

OBJECTIVES: To evaluate the effects of whole-body vibration (WBV) on skeletal muscle activity and power performance of the upper body during decline bench press exercise at different loads. METHODS: Forty-seven healthy young and active male students volunteered. Each performed dynamic decline bench press repetitions with and without WBV (50 Hz, 2.2 mm) applied through a hamstring bridge exercise at three different loads of their 1-repetition maximum (1RM): 30%, 50%, and 70% 1RM. Muscle activity of the triceps brachii (TB), biceps brachii (BB), pectoralis major (PM), and biceps femoris (BF) was measured with surface electromyography electrodes and kinetic parameters of the repetitions were measured with a rotary encoder. RESULTS: WBV increased peak power (PP) output during the 70% 1RM condition (p<0.01). Muscle activity was increased with WBV in the TB and BF muscles at all loads (p<0.05). There were no effects of WBV on BB or PM muscles. CONCLUSION: WBV applied through a hamstring bridge exercise increases TB muscle activity during a decline bench press and this augmentation contributes to an increased peak power at higher loads and increased peak acceleration at lower loads.

The addition of synchronous whole-body vibration to battling rope exercise increases skeletal muscle activity.

OBJECTIVES: To evaluate the effects of performing battling rope exercise with and without the addition of whole-body vibration (WBV) on muscle activity of the leg, trunk, and upper body. METHODS: Twenty-eight recreationally active university students completed 20-s of battling rope undulation for 6 separate conditions: 1) alternating arm motion no WBV -Alt_NoWBV; 2) alternating arm motion 30 Hz low amplitude WBV -Alt_30 Hz-L; 3) alternating arm motion 50 Hz high amplitude -Alt_50 Hz-H; 4) double arm motion no WBV -Double_NoWBV; 5) double arm motion 30Hz low amplitude WBV -Double_30Hz-L; 6) double arm motion 50 'Hz high amplitude -Double_50 Hz-H. Electromyography (EMG) was measured for the gastrocnemius medialis (GM), vastus medialis oblique (VMO), vastus lateralis (VL), rectus abdominis (RA), multifidus (MF), biceps brachii (BB), and triceps brachii (TB) muscles. RESULTS: The double arm motion during undulation resulted in greater (p<0.05) muscle activity in the VMO, VL, RA, and MF muscles while the GM was more active during the alternating arm motion. WBV at 50Hz increased EMG in all muscles measured vs NoWBV and the 30 Hz condition. CONCLUSION: These results are the first to demonstrate that the exercise stimulus of performing battling rope exercise can be augmented by completing the exercise while being exposed to WBV from a ground-based platform.

Sprint interval exercise elicits near maximal peak VO2 during repeated bouts with a rapid recovery within 2 minutes.

AIM: We investigated the cardiorespiratory response during acute sprint interval exercise (SIE; 4 x 30 sec maximal efforts, each separated by 4 min recovery) vs. continuous endurance exercise (CEE; 30 min) at 70% VO2max. METHODS: Oxygen consumption (VO2) and heart rate were measured in 8 males (age: 23±2.3 y, height: 181±6.4 cm, body mass: 78±8.6 kg, VO2max: 52±3.1 ml·kg-1·min-1, mean±SD). Pre-exercise diet was controlled. RESULTS AND CONCLUSION: Total VO2 was greater with CEE vs. SIE (87.6±13.1 vs. 35.1±4.4 L O2) with small differences (P=0.06) in average heart rates (CEE: 157±10 bpm vs. SIE: 149±6 bpm) and peak heart rates (CEE: 166±10 vs. SIE: 173±6; P=0.14). VO2 increased during the sprint bouts (53-72% of VO2max) and attained near maximal values (84-96%) in the immediate recovery period (within 20 sec). Thereafter a rapid decrease occurred so that at 2 min of recovery VO2 was ~1.5 L/min (~38% VO2max). During the remaining 2 min of recovery VO2 declined more slowly to ~1.3 L/min or ~33% of VO2max. Similar heart rate responses with CEE and SIE and a greater VO2 during SIE suggest increased muscle oxygen extraction with SIE, which might explain the greater peripheral adaptations, observed previously with sprint vs. continuous training. The potential value of shorter recovery durations to SIE needs to be examined.

Effects of whole-body vibration with an unstable surface on muscle activation.

The current study examined the effects of using an unstable surface during whole-body vibration (WBV) exercise on leg and trunk muscle activity during a static semi-squat. Twenty-eight recreationally active university students completed 4 different test conditions: 1) stable surface with no WBV; 2) unstable surface with no WBV; 3) unstable surface with 30 Hz WBV low amplitude; and 4) unstable surface with 50 Hz WBV low amplitude. Surface electromyography (sEMG) was measured for the gastrocnemius medialis (GM), vastus medialis oblique (VMO), vastus lateralis (VL), rectus abdominis (RA), and multifidus (MF) muscles. Normalized to the stable condition, WBV at 30 Hz and an unstable surface increased EMG in the GM vs the unstable and stable surfaces (~35%; p<0.05). VMO EMG decreased in the unstable vs stable condition (~20%), WBV at 30 Hz and an unstable surface increased EMG vs all other conditions (~20-40%; p<0.05). MF EMG increased with WBV at 30 Hz (25%; p<0.05) vs the stable condition but not vs all other conditions. Using an unstable surface during WBV exposure increases EMG of muscles in the lower extremities and trunk suggesting the combination of an unstable surface combined with WBV may be an effective modality to further increase EMG.

Acute unilateral leg vibration exercise improves contralateral neuromuscular performance.

OBJECTIVES: To examine the post-exercise cross-transfer effects of acute whole body vibration (WBV). METHODS: Seventeen healthy male volunteers (20.8 ± 1.2 y) performed three unilateral vibration conditions in a randomized order: 1) WBV-50 Hz [high amplitude]; 2) WBV-30 Hz [low amplitude]; and 3) a control no WBV condition (Sham) applied to the dominant leg. Each condition involved maximal voluntary isometric contractions (MVC) followed by three leg press explosive repetitions (40% MVC) with non-dominant and dominant legs; which were conducted prior to and post vibration (immediately; 2 min and 5 min). Surface electromygraphy (sEMG) of the vastus lateralis (VL) and medial gastrocnemius (MG) were measured throughout each condition. RESULTS: A condition x leg x time interaction effect was detected (p=0.001) where 50 Hz-High in the stimulated leg enhanced mean velocity at post-2 min compared to 30 Hz-Low and Sham, remaining elevated at post-5 min. Similarly, 50 Hz-High in the non-stimulated leg increased mean velocity at post-immediately and post-2 min compared to 30 Hz-Low and Sham. There were no changes in sEMG of VL and GM in the stimulated and non-stimulated post-conditions. CONCLUSION: WBV (50 Hz) can augment cross-transfer in neuromuscular performance. WBV could provide an alternate method of unilateral training to promote cross education explosive strength.

Physical activity assessment tools for use in overweight and obese children.

The prevalence of excess weight in children and adults worldwide has increased rapidly in the last 25 years. Obesity is positively associated with increased risk for many health issues such as type 2 diabetes, cardiovascular disease and psychosocial problems. This review focuses on child populations, as it is known that the sedentary behaviors of overweight/obese youth often endure into adulthood. Assessment of physical activity (PA), among other factors such as diet and socio-economic status, is important in understanding weight variation and in designing interventions. This review highlights common subjective and objective PA assessment tools, the validity of these methods and acceptable ways of collecting and interpreting PA data. The aim is to provide an update on PA assessment in overweight/obese children, highlighting current knowledge and any gaps in the literature, in order to facilitate the use of PA assessments and interventions by health-care professionals as well as suggest future research in this area.

Transmission of acceleration from a synchronous vibration exercise platform to the head.

Exercise vibration platforms are becoming commonplace in homes and fitness centers. However, excessive mechanical energy transferred to the head and eye can cause injury. The purpose of this study was to evaluate how changes in platform frequency and knee flexion angle affect acceleration transmission to the head. Participants (N=12) stood on a whole-body vibration platform with knee flexion angles of 0°, 20°, and 40° to evaluate how changes in knee flexion affected head acceleration. 7 specific platform frequencies were tested between 20-50 Hz at 2 peak-to-peak displacement settings (1 and 2 mm nominal). Accelerations were measured with triaxial accelerometers at the platform and head to generate transmissibility ratios. Platform-to-head transmissibility was not significantly different between the 2 platform peak-to-peak amplitudes (P>0.05). Transmissibility measures varied depending on platform frequency and knee angle (P < 0.05). Flexing the knees resulted in reduced head transmissibility at all frequencies (P<0.05). Platform-to-head transmissibility values exceeded 1.0 at both 20 and 25 Hz platform vibration frequencies with the knees in full extension. To reduce the risk of injury to structures of the head during vibration exercise, using platforms frequencies below 30 Hz with small knee flexion angles (< 40°) should be avoided.

Impaired superficial femoral artery vasodilation and leg blood flow in young obese women following an oral glucose tolerance test.

This study was designed to test the hypothesis that glucose ingestion following an overnight fast increases leg vascular conductance (LVCd) and superficial femoral artery (SFA) vasodilation in lean but not obese young women. Obese (23.5 ± 4.0 years, 84.7 ± 14.7 kg, 37.2% ± 6.4% fat; mean ± SD, n = 8) and lean (23.8 ± 2.4 years, 60.6 ± 4.0 kg, 22.3% ± 2.8% fat; n = 8) women arrived in the laboratory at 0830 h after a 12-h overnight fast for body composition (densitometry) assessment. Then, capillary blood glucose (BGlu), plasma insulin, heart rate, cardiac output, mean arterial pressure, leg blood flow (Doppler ultrasound), and LVCd were measured (after 15 min in the supine position), and at 30-min intervals for 2 h following glucose ingestion (75 g glucose load, 12.5% solution). Fasting BGlu concentration was not different between groups (obese = 5.1 ± 0.47 vs. lean = 4.9 ± 0.37 mmol·L(-1), p = 0.71) but 60, 90, and 120 min post ingestion BGlu was elevated (p ≤ 0.03) in the obese women. Insulin differences were not significant. Fasting LVCd was not different between groups (lean = 0.72 ± 0.49 vs. obese = 0.70 ± 0.19 mL·min(-1)·mm Hg(-1); p = 0.48); however, LVCd, as well as Δ in SFA diameter were significantly elevated (p ≤ 0.04) in the lean compared with the obese group at 60, 90, and 120 min postglucose ingestion (LVCd, peak lean = 1.4 ± 0.5 vs. peak obese = 0.8 ± 0.1 mL·min(-1)·mm Hg(-1); Δ in SFA, peak lean = 0.51 ± 0.30 vs. peak obese = 0.09 ± 0.45 mm). The reduced LVCd following glucose ingestion could contribute to impaired glucose tolerance. Further, the lack of SFA dilation may be evidence of impaired vascular insulin responsiveness in these obese young women.