It is important to understand the effects of rapid changes in weight on neuromuscular functions of combat athletes. The purpose of this case study was to investigate time-course changes in muscle ...strength, muscle size, and neural input during rapid weight loss in a professional boxer. One professional male boxer (26 yr) participated in two matches during measurements: welterweight (66.6 kg; weight loss: WL) and super welterweight (69.85 kg; control: CON). His muscle contraction properties and body composition were measured from 6 wk (baseline) before the matches to 1 wk after them. Maximal voluntary isometric knee extension torque, muscle cross-sectional area (mCSA) of the vastus lateralis using ultrasound, and high-density surface electromyography of the vastus lateralis during submaximal ramp-up contraction were measured. Individual motor units were identified, and modified discharge rates were calculated from a regression line between the recruitment threshold and discharge rates at 60%-70% of maximum torque according to the baseline value. His body weights for WL and CON decreased from 70.80 and 71.42 kg at the baseline to 68.75 and 71.36 kg immediately before the matches, respectively. Muscle strength changed little for either match. For WL, skeletal muscle mass and mCSA decreased, but there was no decrease for CON. The modified motor unit discharge rate for WL increased immediately before the match compared with other periods but did not change for CON. After rapid weight loss, neural input increased to compensate for lost muscle mass, and muscle strength was maintained.
This case study found that neural input to muscle, which was evaluated by high-density surface electrocardiography, increased to compensate for the decline of body weight and muscle mass and to maintain muscle strength during rapid weight loss, while neuromuscular characteristics were not markedly changed during no significant weight loss.
Alaska pollack protein (APP), has been reported as a protein source that can enhance muscle hypertrophy more than other protein sources in animal studies. This study aimed to examine the effects of ...APP ingestion on muscle quantity and quality in young adults. Fifty-five young college students were assigned to two groups: APP and placebo (whey protein: WP) groups, and instructed to ingest 4.5 g of each protein in addition to daily meals, and to maintain their usual daily physical activities for 3 mo. Twenty-one and 23 students completed the intervention and were analyzed in APP and WP groups, respectively. The maximum knee extension torque significantly increased in both groups during the intervention. The motor unit discharge rate, which is an indicator of activation, for a given force level significantly decreased in both groups during the intervention, but its decrease in the APP group was significantly greater than in the WP group. Echo intensity of the vastus lateralis evaluated by ultrasound images significantly decreased in both groups. The muscle thickness and skeletal muscle mass did not change. Small amount of additional APP intake induces greater effects on neural activation than WP, suggesting the greater neural economy of generation of force.
Abstract
Assessments of both neural and muscular adaptations during interventions would provide valuable information for developing countermeasures to age-related muscle dysfunctions. We investigated ...the effect of fish protein ingestion on training-induced neural and muscular adaptations in older adults. Twenty older adults participated 8 weeks of isometric knee extension training intervention. The participants were divided into two groups who took fish protein (n = 10, Alaska pollack protein, APP) or casein (n = 10, CAS). Maximal muscle strength during knee extension, lower extremity muscle mass (body impedance method), and motor unit firing pattern of knee extensor muscle (high-density surface electromyography) were measured before, during, and after the intervention. Muscle strength were significantly increased in both CAS (124.7 ± 5.8%) and APP (117.1 ± 4.4%) after intervention (p < .05), but no significant differences between the groups were observed (p > .05). Significant increases in lower extremity muscle mass from 0 to 8 weeks were demonstrated only for APP (102.0 ± 3.2, p < .05). Greater changes in motor unit firing pattern following intervention were represented in CAS more than in APP. These results suggest that nutritional supplementations could modulate neural and muscular adaptations following resistance training and fish protein ingestion preferentially induces muscular adaptation without the detectable neural adaptation in older adults.
We investigated the effect of resistance training and fish protein intake on the motor unit firing pattern and motor function in elderly. Fifty healthy elderly males and females (69.2 ± 4.7 years) ...underwent 6 weeks of intervention. We applied the leg-press exercise as resistance training and fish protein including Alaska pollack protein (APP) as nutritional supplementation. Subjects were divided into four groups: fish protein intake without resistance training (APP-CN,
= 13), placebo intake without resistance training (PLA-CN,
= 12), fish protein intake with resistance training (APP-RT,
= 12), and placebo intake with resistance training (PLA-RT,
= 13). Motor unit firing rates were calculated from multi-channel surface electromyography by the Convolution Kernel. For the chair-stand test, while significant increases were observed at 6 weeks compared with 0 week in all groups (
< 0.05), significant increases from 0 to 3 weeks and 6 weeks were observed in APP-RT (18.2 ± 1.9 at 0 week to 19.8 ± 2.2 at 3 weeks and 21.2 ± 1.9 at 6 weeks) (
< 0.05). Increase and/or decrease in the motor unit firing rate were mainly noted within motor units with a low-recruitment threshold in APP-RT and PLA-RT at 3 and 6 weeks (12.3 pps at 0 week to 13.6 pps at 3 weeks and 12.1 pps at 6 weeks for APP-RT and 12.9 pps at 0 week to 13.9 pps at 3 weeks and 14.1 pps at 6 weeks for PLA-RT at 50% of MVC) (
< 0.05), but not in APP-CN or PLA-CN (
> 0.05). Time courses of changes in the results of the chair-stand test and motor unit firing rate were different between APP-RT and PLA-RT. These findings suggest that, in the elderly, the effect of resistance training on the motor unit firing rate is observed in motor units with a low-recruitment threshold, and additional fish protein intake modifies these adaptations in motor unit firing patterns and the motor function following resistance training.
This study aimed to investigate the effect of milk fat globule membrane (MFGM) supplementation on motor unit adaptation following resistance training in older adults. Twenty‐five older males and ...females took MFGM (n = 12) or a placebo (PLA; n = 12) while performing 8 weeks of isometric knee extension training. During the training, the motor unit firing pattern during submaximal contractions, muscle thickness, and maximal muscle strength of knee extensor muscles were measured every 2 weeks. None of the measurements showed significant differences in muscle thickness or maximal muscle strength (MVC) between the two groups (p > .05). Significant decreases in motor unit firing rate following the intervention were observed in PLA, that is, 14.1 ± 2.7 pps at 0 weeks to 13.0 ± 2.4 pps at 4 weeks (p = .003), but not in MFGM (14.4 ± 2.5 pps to 13.8 ± 1.9 pps). Motor unit firing rates in MFGM were significantly higher than those in PLA at 2, 4, 6, and 8 weeks of the intervention, that is, 15.1 ± 2.3 pps in MFGM and 14.5 ± 3.3 pps in PLA at 70% of MVC for motor units recruited at 40% of MVC at 6 weeks (p = .034). Significant differences in firing rates among motor units with different recruitment thresholds were newly observed following the resistance training intervention in MFGM, indicating that motor unit firing pattern is changed in this group. These results suggest that motor unit adaptation following resistance training is modulated by MFGM supplementation in older adults.
The positive effect of milk fat globule membrane (MFGM) supplementation with exercise on age‐related dysfunctions in neuromuscular system had been reported in animal and human studies. This study found that MFGM supplementation with exercise can modify adaptations in motor unit firing pattern in older adults. Whereas the same exercise regimen was applied, different neural adaptation may be able to induce by ingestion of MFGM in older adults.
Nutritional supplementation in conjunction with exercise is of interest for the prevention or improvement of declines in motor performances in older adults. An understanding of the effects on both ...young and older adults contributes to its effective application. We investigated the effect of fish protein ingestion with resistance training on neural and muscular adaptations in young adults using interventions and assessments that have already been tested in older adults.
Eighteen young adults underwent 8 weeks of isometric knee extension training. During the intervention, nine participants ingested 5 g of fish protein (
= 9, Alaska pollack protein, APP), and the other nine participants ingested casein as a control (
= 9, CAS) in addition to daily meals. Before, during, and after the intervention, the isometric knee extension force, lower extremity muscle mass, and motor unit firing pattern of knee extensor muscles were measured.
Maximum voluntary contraction (MVC) was significantly increased in both APP and CAS groups from 0 weeks to 4, 6, and 8 weeks of intervention (
< 0.001), but there were no significant differences between the groups (
= 0.546-0.931). Muscle mass was not significantly changed during the intervention in either group (
= 0.250-0.698). Significant changes in motor unit firing rates (
= 0.02 and 0.029 for motor units recruited at 20-40% of MVC and at 40-60%) were observed following the intervention in the APP but not CAS (
= 0.120-0.751) group.
These results suggest that dietary fish protein ingestion changes motor unit adaptations following resistance training in young adults.
A previously developed current swimming pool for mice has been used to evaluate many food components that enhance endurance exercise performance. In this article, to improve reproducibility, ...reliability and sensitivity of this assay system, we improved the spout part to generate a uniform current and divided the pool into six lanes to avoid physical interference between swimming mice. The stability of the current flow was assessed by measuring the surface current speed and water volume from the spout part. Maximum swimming times of ddY and BALB/c mice were measured to assess the reproducibility of the maximum swimming time. The improvement in sensitivity compared to the original equipment was estimated under three physiological conditions: low carbohydrate diet feeding, low blood hemoglobin level, and carbohydrate supplementation during exercise. The new spout part improved uniformity and quick adjustment of surface current, yielding an increase of workload in a stepwise manner during swimming. Exercise workload was increased in proportion to surface current speed, as evidenced by cadence of kicks and serum lactic acid levels. The improved swimming pool showed higher reproducibility of swimming time until fatigue (p0.0001). Correspondence between blood hemoglobin concentration and swimming time was improved in the swimming pool. The improved swimming pool yielded higher sensitivity for low carbohydrate diet feeding (p0.0001) and carbohydrate supplementation during exercise (p0.01) compared to the original swimming pool. The improvement of the Swimming pool achieved higher sensitivity and reproducibility in assessing various diet and food components compared to the original swimming pool.
Neural and morphological adaptations determine gains of muscle strength. For youth athletes, the importance of morphological adaptation is typically highlighted based on the change in maturity ...status. However, the long-term development of neural components in youth athletes remains unclear. The present study investigated the longitudinal development of muscle strength, muscle thickness (MT), and motor unit firing activity of the knee extensor and their relationships in youth athletes. Seventy male youth soccer players (mean ± SD age = 16.3 ± 0.6 years) performed neuromuscular, maximal voluntary isometric contraction (MVC), and submaximal ramp contraction (at 30 and 50% MVC) tests with knee extensors, two times with a 10-month measurement interval. High-density surface electromyography was recorded from the vastus lateralis and decomposed to identify each individual motor unit activity. MT was evaluated by the sum of the vastus lateralis and vastus intermedius thicknesses. Finally, sixty-four participants were employed to compare MVC and MT, and 26 participants were employed to analyze motor unit activity. MVC and MT were increased from pre to post (
p
< 0.05, 6.9 and 1.7% for MVC and MT, respectively). Y-intercept of the regression line between median firing rate vs. recruitment threshold was also increased (
p
< 0.05, 13.3%). Multiple regression analysis demonstrated that the gains of both MT and Y-intercept were explanatory variables for the gain of strength. These findings suggest that the neural adaptation could also make the important contribution to the strength gain for the youth athletes over a 10-month training period.
Chromium (Cr) is an essential trace element and is important for normal carbohydrate metabolism, and its deficiency in animals can cause a diabetic-like state. Human and experimental animal studies ...suggest that urinary Cr excretion is increased in diabetic populations. To investigate whether hyperglycemia-induced elevation of urinary Cr excretion reduces tissue Cr storage conditions, we assessed total Cr balance and Cr distribution in streptozotocin (STZ)-induced diabetic mice. Male C57BL mice were randomly assigned to STZ or control groups and their urine was collected 7, 14, 21 and 28 d after STZ injection. An inductively coupled plasma mass spectrometry instrument equipped with a dynamic reaction cell was used for determination of Cr in urine, plasma and tissues samples. The urinary excretions of Cr were 15.4+-3.0 and 356+-62 ng/d, and the renal Cr concentrations were 0.85+-0.12 and 0.17+-0.03 ng/mg for the control and diabetes groups, respectively (p0.01), after 28 d. The Cr balance in STZ-treated mice was distinctly negative due to the increase in urinary Cr loss (p0.01). These results suggest that in mice, STZ induces a reduction in renal Cr concentration and total negative Cr balance caused by an increase in urinary Cr output.
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