Amino acid metabolism, branched-chain amino acid feeding and brain monoamine function

Several papers in the present symposium emphasize the importance and interplay of carbohydrate and fat metabolism during exercise of varying intensities and duration. In constrast, amino acid metabolism is deemed to make only a minimal contribution to the provision of energy for the working muscle and is, with few exceptions, ignored. Equally, the mechanisms of what is termed ‘central fatigue’, i.e. fatigue associated with alterations in the functioning of the brain or central nervous system (CNS), are largely unexplored. However, several papers over the past few years have promoted an attractive role for certain amino acids as substrates for intermediary metabolism and precursors of brain neurotransmitters. The focus of the present paper is the potential interplay between peripheral substrate utilization, amino acid metabolism, brain neurotransmitter function and fatigue. For the purpose of the present symposium only experimental data obtained from human subjects will be considered

The effect of feeding a dairy-based calcium supplement on exercise-induced disturbance of bone turnover in healthy human subjects

no abstract availabl

The effect of hydration status on the measurement of lean tissue mass by dual-energy X-ray absorptiometry

Athletes cycle between exercise and recovery. Exercise invokes changes in total body water from thermal sweating, muscle and hepatic glycogen depletion and metabolic water loss. Recovery from exercise results in rehydration, substrate repletion, and possible glycogen supercompensation. Such changes may corrupt the measurement of hydrated tissues, such as lean tissue mass (LTM), by dual-energy X-ray absorptiometry (DXA). The purpose of this study was to determine the effect of exercise and thermal dehydration and subsequent glycogen supercompensation on DXA-based measurement of body composition.Twelve active adult (18-29 years) males exercised at 70% VO2max on a cycle ergometer in a thermal environment (30 A degrees C) to induce a 2.5% reduction in body mass. Participants subsequently underwent a glycogen supercompensation phase, whereby a high carbohydrate diet (8-12 g/kg body mass/day) was consumed for a 48-h period. Whole-body DXA measurement was performed at baseline, following exercise and supercompensation.Following exercise, mean body mass decreased by -1.93 kg (95% CI -2.3, -1.5), while total LTM decreased by -1.69 kg (-2.4, -1.0). Supercompensation induced a mean body mass increase of 2.53 kg (2.0, 3.1) and a total LTM increase of 2.36 kg (1.8, 2.9). No change in total fat mass or bone mineral content was observed at any timepoint.Training regimens that typically induce dehydration and nutrition regimens that involve carbohydrate loading can result in apparent changes to LTM measurement by DXA. Accurate measurement of LTM in athletes requires strict observation of hydration and glycogen status to prevent manipulation of results

The effect of whey protein supplementation on the temporal recovery of muscle function following resistance training: a systematic review and meta‐analysis

Whey protein (WP) is a widely consumed nutritional supplement, known to enhance strength and muscle mass during resistance training (RT) regimens. Muscle protein anabolism is acutely elevated following RT, which is further enhanced by WP. As a result, there is reason to suggest that WP supplementation may be an effective nutritional strategy for restoring the acute loss of contractile function that occurs following strenuous RT. This systematic review and meta analysis provides a synthesis of the literature to date, investigating the effect of WP supplementation on the recovery of contractile function in young, healthy adults. Eight studies, containing 13 randomised control trials (RCTs) were included in this review and meta‐analysis, from which individual standardised effect sizes (ESs) were calculated, and a temporal overall ES was determined using a random‐effects model. Whilst only half of the individual studies reported beneficial effects for WP, the high‐quality evidence taken from the 13 RCTs was meta‐analysed, yielding overall positive small to medium effects for WP from < 24 to 96 h (ES range = 0.4 to 0.7), for the temporal restoration of contractile function compared to the control treatment. Whilst the effects for WP were shown to be consistent over time, these results are limited to 13 RCTs, principally supporting the requirement for further comprehensive research in this area

Sex differences in the temporal recovery of neuromuscular function following resistance training in resistance trained men and women 18 to 35 Years

To investigate sex differences in the temporal recovery of neuromuscular function following resistance training (RT), eleven men and eight women 18–35 years completed a single RT bout (barbell back-squats, 80 % 1RM, 5 sets × 5 reps, 25 % duty cycle, then 1 set × max reps). Measures of muscle function (isometric, concentric, eccentric knee extensor strength, and countermovement jump (CMJ) height), serum creatine kinase activity (CK) and lower-body muscle pain were assessed before RT (0 h), +4 h, +24 h, +48 h, and +72 h post-RT. Data are mean % change from PRE (SD) and effect size (ω2, d). Men and women had similar RT-experience (men, 2.1 (0.8) years vs. women 2.4 (1.0) years, P = 0.746, and d = 0.3) and 1RM strength per kg lean mass (men, 1.9 (0.2) kg⋅kg-1 vs. women, 1.8 (0.3) kg⋅kg-1, P = 0.303, and d = 0.3). A 36 (12)% increase in lower-body muscle pain was reported following RT (P 0.9). There was an absence of any overt change in CK [+24 h, 74 (41) IU⋅L-1; pooled mean (SD)]. Decrements in knee extensor strength and CMJ height were observed +4 to +72 h for both men and women (P < 0.05, ω2 = 0.19–0.69). Sex differences were apparent for CMJ height (+24 h men, -10 (6)% vs. women, -20 (11)%, P < 0.001, and d = 1.8) and isokinetic concentric strength (+24 h men, -10 (13)% vs. women -25 (14)%, P = 0.006, and d = 1.8), with a more pronounced loss and prolonged recovery in women compared to men (e.g., CMJ + 72 h men, -3 (6)% vs. women, -13 (12)%, P = 0.051, and d = 1.1). We conclude that the different temporal recovery patterns between men and women are not explicable by differences in muscle strength, RT performance, experience, muscle damage or fatigability

Age-group differences in the performance of selected tests of physical function and association with lower extremity strength

. Background and Purpose: It is not known whether short functional performance tests used in aging research are appropriate for use in healthy older adults. The purpose of this study was to investigate age-group differences (sixth decade vs seventh decade) in selected functional performance tests and the association between lower extremity strength and functional performance. Methods: One hundred fifty-nine (18.2% [n = 29] male) healthy older adults (mean (standard deviation) age 60.4 (5.3) years), adults were recruited from the University of Limerick Campus Community. Knee extensor (KE) peak torque (PT) was assessed from a maximal voluntary isometric contraction. Subsequently, participants completed 10-m maximal and habitual gait speed tests, 5 repetition and 30-second chair rise tests, and a 900-m gait speed test. Results and Discussion: There was no difference in 10-m gait speed between those in the sixth and seventh decades (P > .05). Compared with the sixth decade, those in the seventh decade required an extra 39 seconds to complete 900 m, an extra 0.6 seconds to complete 5 chair rises and performed 2 fewer chair rises in a 30-second time period (P < .05). All tests had a weak association with KE strength (r = 0.226-0.360; P < .05), except for 900-m gait speed that had a moderate association (r = −0.537; P < .001). Our findings suggest that gait speed tests of 10 m or less cannot detect age-related difference in functional capacity when used in healthy older adults. Conclusion: Extended physical performance tests should be used in aging research on healthy older adults

Temporal change in biomarkers of bone turnover following late evening ingestion of a calcium-fortified, milk-based protein matrix in postmenopausal women with osteopenia

he diurnal rhythm of bone remodeling suggests nocturnal dietary intervention to be most e ective. This study investigated the e ect of bedtime ingestion of a calcium-fortified, milk-derived protein matrix (MBPM) or maltodextrin (CON) on acute (0–4 h) blood and 24-h urinary change in biomarkers of bone remodeling in postmenopausal women with osteopenia. In CON, participants received 804 52 mg calcium, 8.2 3.2 g vitamin D and 1.3 0.2 g/kg BM protein per day. MBPM increased calcium intake to 1679 196 mg, vitamin D to 9.2 3.1 g and protein to 1.6 0.2 g/kg BM. Serum C-terminal cross-linked telopeptide of type I collagen (CTX) and procollagen type 1 amino-terminal propeptide (P1NP), and urinary N-telopeptide cross-links of type I collagen (NTX), pyridinoline (PYD) and deoxypyridinoline (DPD) was measured. Analyzed by AUC and compared to CON, a 32% lower CTX (p = 0.011, d = 0.83) and 24% (p = 0.52, d = 0.2) increase in P1NP was observed for MBPM. Mean total 24 h NTX excreted in MBPM was 10% (p = 0.035) lower than CON. Urinary PYD and DPD were una ected by treatment. This study demonstrates the acute e ects of bedtime ingestion of a calcium-fortified, milk-based protein matrix on bone remodeling

A reference base for age-related decrease in lean tissue mass: whole body and segmental lean tissue mass in healthy young Irish men and women

no abstract availabl