Reliability of heart rate variability measures at rest and during light exercise in children

Abstract

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...

Short-Term Heart Rate Variability in a Population-Based Sample of 10-Year-Old Children

“…Interestingly, when assessed separately, a significant association between 24-h physical activity and diminished sympathovagal imbalance in children was observed [5,48]. However, while larger BMI was not associated with HRV, larger waist circumference was related to reduced VLF, which is partly consistent with past pediatric findings of greater obesity linked to reduced HRV [16,22,33].…”

“…When all covariates were included in the models simultaneously, heart rate (β avg = −0. [19,48]. No comparisons could be made for SDANN and SDNNi, as they are infrequently reported in studies.…”

Moderate-term reproducibility of heart rate variability during rest and light to moderate exercise in children

“…Compared to previous reliability studies, the current study reported greater reproducibility (e.g., lower CV and/or lower LOA) for HRV during rest and light exercise over the 8-week period (11,18,37). Previous recommendations of greater control of external influences such as time of recording, overnight fast and restriction of tobacco or caffeine (11,18,37) were followed in the current study and may have contributed to the greater HRV reliability compared to these prior studies.…”

Effects of eight weeks of physical training on physical performance and heart rate variability in children

“…Winsley et al (2003) [16] pointed out the importance of tight control of external influences. In the present research that was not achieved at all times.…”