Objective: To examine the absolute and relative changes in skeletal muscle (SM) size using whole body magnetic resonance imaging (MRI) in response to heavy resistance training (RT). Method: Three young men trained three days a week for 16 weeks. Results: MRI measured total SM mass and fat free mass (FFM) had increased by 4.2 kg and 2.6 kg respectively after resistance training. Conclusions: RT induces larger increases in SM mass than in FFM. RT induced muscle hypertrophy does not occur uniformly throughout each individual muscle or region of the body. Therefore the distribution of muscle hypertrophy and total SM mass are important for evaluating the effects of total body RT on muscle size.A ccurate measurements of skeletal muscle (SM) mass and distribution in humans are important for studies of SM hypertrophy response to heavy resistance training (RT). Currently, the most accurate in vivo methods of measuring SM mass are multiscan magnetic resonance imaging (MRI) and computed tomography.1 Despite its safety, most MRI studies have only evaluated regional-for example, arms, trunk, and legs-SM mass. 1 We recently reported whole body MRI using a contiguous slice by slice (no interslice gap) method to evaluate total SM mass and its distribution.2 Using this approach, the distribution of RT induced whole body SM hypertrophy can be investigated.To date, most studies 3 4 have only evaluated limb muscle hypertrophy, and very few have reported RT induced muscle hypertrophy in the trunk region.5 More importantly, the distribution of the relative increases in RT induced muscle hypertrophy has not been reported. Thus the purpose of this pilot study was to examine the absolute and relative changes in SM size using contiguous whole body MRI scans in response to RT. METHODSThree healthy young men (age 20-21 years) volunteered for the study. All were physically active, but none had participated in RT before the start of the programme. All subjects signed informed consent documents. The department's ethical commission approved the study.RT was carried out three days a week for 16 weeks. Three lower body (squat, knee extension, and knee flexion) and two upper body (bench press and latissimus dorsi pull down) exercises were performed. Workouts consisted of a warm up set followed by three sets to failure of 8-12 repetitions for each of the five exercises. The loads were progressively increased to maintain this range of repetitions per set. One repetition maximum (1RM) strength was determined by progressively increasing the weight lifted until the subject failed to lift the weight through a full rage of motion. Strength of the squat was assessed using the 3RM test.Total body SM distribution and mass were measured using an MRI 1.5-T scanner (GE Signa, Milwaukee, Wisconsin, USA) with spin echo sequence (TR, 1500 milliseconds; TE, 17 milliseconds).2 Contiguous transverse images with 1.0 cm slice thickness (no interslice gap) were obtained from the first cervical vertebra to the ankle joints for each subject. Four sets extended from the...

The aim of this study was to investigate the effects of age and recovery duration on performance during multiple treadmill sprints. Twelve boys (11.7 +/- 0.5 y) and thirteen men (22.1 +/- 2.9 y) performed ten consecutive 10-s sprints on a non-motorised treadmill separated by 15-s (R15) and 180-s (R180) passive recovery intervals. Mean power output (MPO), mean force output (MFO), running velocity, step length, and step rate were calculated for each sprint. Capillary blood samples were drawn from the fingertip at rest and 3 min after the tenth sprint to measure the lactate accumulation (Delta [La]). With R15, all mechanical parameters decreased significantly less in the boys than in the men over the ten sprints (MPO: - 28.9 vs. - 47.0 %, MFO: - 13.1 vs. - 25.6 %, running velocity: - 18.8 vs. - 29.4 %, p < 0.001, respectively). With R180, all mechanical values remained unchanged in the boys. In the men, MPO and MFO significantly decreased over the ten sprints (- 7.8 % and - 4.6 %, p < 0.05, respectively). The running velocity, however, did not decrease because the decrease in step rate (p < 0.001) was compensated by an increase in step length. For either recovery interval, Delta [La] values were higher in the men compared to the boys (R15: 12.7 vs. 7.7 mmol . L (-1), p < 0.001, R180: 10.7 vs. 7.7 mmol . L (-1), p < 0.05). To conclude, the boys maintained more easily their running performance than the men during repeated treadmill sprints with R15. Three-minute recovery periods were sufficient in the boys to repeat short running sprints without substantial fatigue. Despite the decrease in power and force outputs with R180, the young men were able to maintain their running velocity during the test.

Heart rate variability (HRV) measurements provide information on the autonomic nervous system and the balance between parasympathetic and sympathetic activity. A high HRV can be advantageous, reflecting the ability of the autonomic nervous system to adapt, whereas a low HRV can be indicative of fatigue, overtraining or health issues. There has been a surge in wearable devices that claim to measure HRV. Some of these include spot measurements, whilst others only record during periods of rest and/or sleep. Few are capable of continuously measuring HRV (≥24 h). We undertook a narrative review of the literature with the aim to determine which currently available wearable devices are capable of measuring continuous, precise HRV measures. The review also aims to evaluate which devices would be suitable in a field setting specific to military populations. The Polar H10 appears to be the most accurate wearable device when compared to criterion measures and even appears to supersede traditional methods during exercise. However, currently, the H10 must be paired with a watch to enable the raw data to be extracted for HRV analysis if users need to avoid using an app (for security or data ownership reasons) which incurs additional cost.

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15 kg, 30 kg, 40 kg or 50 kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40 kg only). FVC and FEV 1 were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breathsÁmin À1 ) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases.Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.