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.

Purpose: Contributions of neural and muscular factors to muscle strength change with growth, but such changes remain unclear in young populations. This study aimed to clarify the association between muscle strength and neural and muscular factors in youth athletes. Methods: Maximal voluntary contraction (MVC) during isometric knee extension, the motor unit firing rate (MUFR), and muscle thickness (MT) of the vastus lateralis were measured in 70 youth male soccer players (mean [SD]; chronological age = 16.3 [0.6] y, peak height velocity age = 13.1 [1.0] y). MUFR and MT were measured with high-density surface electromyography and ultrasonography, respectively. Results: For MUFR and MT, correlations with MVC were calculated and the values of different MVC groups were compared. A significant correlation between MVC and MT (r = .49, P &lt; .01) was noted, but not MUFR (r = .03, P &gt; .05). There was also no significant correlation between MT and MUFR (r = −.33, P &gt; .05). In addition, comparison among groups (higher-/middle-/lower-strength groups) revealed that MT in the lower-strength group was significantly lower than in middle-and higher-strength groups (P &lt; .01). Conclusion: In youth athletes, muscle strength is associated with muscular factors, rather than neural factors, and muscular and neural factors may independently contribute to muscle strength.

Introduction Neuromuscular electrical stimulation (NMES) induces involuntary muscle contraction, preferentially promotes anaerobic metabolism, and is applicable for increasing exercise intensity. This study aimed to assess whether superimposing NMES onto moderate-intensity voluntary exercise imitates physiological adaptations that occur in response to vigorous voluntary exercise. Methods Eight participants trained with a cycling ergometer at 100% of the ventilatory threshold (VT) (73.3% of peak oxygen consumption) (VOL), and another nine participants trained with the cycling ergometer at 75% of VT (56.2% of peak oxygen consumption) with subtetanic NMES applied to the gluteus and thigh muscles (VOLES), matched to VOL training sessions, for nine weeks. Results Rating of perceived exertion (RPE) in VOLES (12.00 +/- 1.50) was significantly lower than in VOL (14.88 +/- 1.81) (p < 0.05) during training sessions. Peak power output during the exercise tolerance test was increased in VOL and VOLES following interventions. Oxygen consumption and heart rate (HR) at VT and blood lactate concentration (BLC) at < VT were decreased from before (PRE) to after (POST) training interventions for both VOL and VOLES. There were no significant differences in absolute changes from PRE to POST for peak power output and oxygen consumption, HR, and BLC at a submaximal intensity between VOL and VOLES. Conclusion Our results suggest that both superimposing subtetanic NMES onto moderate-intensity voluntary exercise and vigorous voluntary intensity exercise induce the improvement in cardiovascular and metabolic systems, but the adaptation of former method is provided without perceived strenuous exertion.

In elite fencers, muscle strength and muscle mass of the front leg (FL) are greater than those of the back leg (BL) due to characteristic physiological and biomechanical demands placed on each leg during fencing. However, the development of laterality in their neural and muscular components is not well-understood. The present study investigated neuromuscular characteristics of FL and BL in junior fencers. Nineteen junior fencers performed neuromuscular performance tests for FL and BL, separately. There were no significant differences in the isometric knee extension strength (MVC), unilateral vertical jump (UVJ), vastus lateralis muscle thickness (MT), or motor unit firing rate of the vastus lateralis muscle (MUFR) between FL and BL (p > 0.05). In subgroup analyses, a significantly greater MUFR in FL than BL was noted only in fencers with > 3 years of fencing experience, and significantly greater UVJ in FL than BL was observed solely in fencers with < 3 years of fencing experience (p < 0.05). Strong positive correlations between FL and BL were identified in MVC, MT, and MUFR in fencers with > 3 years of fencing experience, but not in those with < 3 years of experience. These findings suggest that in junior fencers, laterality in neuromuscular performance has not manifested, whereas longer fencing experience induces fencing-dependent laterality in neural components, and laterality in dynamic muscle strength is decreased with fencing experience.

Introduction: Self-massage using a foam roller (foam rolling) has been used to improve joint range of motion (ROM). However, the effect of foam rolling on the morphology of a targeted muscle, tendon, and muscle-tendon unit (MTU) has not been fully clarified. This study aimed to investigate extensibility changes in the gastrocnemius muscle (GM), MTU, and the Achilles tendon (AT) in terms of maximum ankle dorsiflexion (max-DF) following a foam rolling intervention. This was an interventional study with no controls. Methods: Study participants comprised 10 male and female students (mean [standard deviation]: 22.7 [2.5] years; height, 164.2 [6.7] cm; weight, 57.9 [7.9] kg). The foam rolling intervention was performed on the right leg plantar flexor muscles for 3 min. The outcomes were max-DF with specified resistance values (ROM-SR) and non-specified resistance values (ROM-NSR) and GM, MTU, and AT extensibility. An ultrasound device was used to determine the rate of change by subtracting the value in a neutral ankle joint position (0 & DEG;) from the ankle max-DF to identify GM, MTU, and AT extensibility. All outcomes were measured pre-and post-intervention. Results: The range of ankle joint dorsiflexion increased significantly following the foam rolling intervention (D: ROM-SR, +4.35 [5.79]; ROM-NSR, +4.18 [4.43]), whereas GM extensibility increased 4.0 mm, although no significant difference was observed pre-and post-intervention. Conclusion: Foam rolling was effective in increasing ankle joint dorsiflexion ROM. Moreover, it was suggested that the GM morphology might be affected by the intervention. (C) 2022 Elsevier Ltd. All rights reserved.

ABSTRACT: Yoshimura, A, Inami, T, Schleip, R, Mineta, S, Shudo, K, and Hirose, N. Effects of self-myofascial release using a foam roller on range of motion and morphological changes in muscle: a crossover study. J Strength Cond Res 35(9): 2444-2450, 2021-Self-myofascial release using a foam roller (FR) is effective in improving range of motion (ROM) in at least some conditions. However, its mechanism is still unclear. Therefore, this study investigated potential acute muscle morphological changes after the FR intervention and aimed to clarify the mechanism of increases in ROM by the FR intervention. We hypothesized that the FR intervention may increase ROM because of changes in fascicle length (FL) and aponeurosis displacement. This crossover study, involving 22 male university students (21.5 ± 1.3 years, 170.6 ± 4.0 cm, and 64.1 ± 8.9 kg; mean ± SD), compared the FR intervention targeting the gastrocnemius muscle with the control trial. The outcome measures were maximum passive ankle ROM, morphology of the gastrocnemius muscle (FL and aponeurosis displacement) during passive ankle plantar flexor movement, degree of pain during the FR intervention, and sensation of the triceps surae muscle. Although ROM of both dorsiflexion and plantar flexion increased significantly after the FR intervention (p < 0.01), no significant differences were found in FL and aponeurosis displacement before and after the FR intervention. The mean perception of pain during the FR intervention was rated as "slightly uncomfortable," corresponding to a 2.3 ± 2.4-cm on a 9.5-cm visual analog scale. We found that the FR intervention did not influence the morphology of muscle. It is necessary to investigate other factors related to ROM as the next step of this study.

Long-distance running results in lowering of the foot medial longitudinal arch, but it is unknown whether the left and right arches decrease equally. This study aimed to determine whether foot arch asymmetry increases upon completion of a full marathon and to identify factors capable of explaining the degree of asymmetry of navicular height and navicular height displacement. The three-dimensional foot posture data of 74 collegiate runners were obtained using an optical foot scanner system before (PRE) and immediately after (POST) a full marathon. The navicular height and arch height ratio (normalised navicular height by foot length) of both feet significantly decreased from PRE to POST full marathon completion (44.3 ± 6.3 mm versus 40.8 ± 6.5 mm, 17.8 ± 2.5 versus 16.6 ± 2.7, respectively; p < 0.001, both). The asymmetry of the arch height ratio was significantly greater POST than PRE marathon. Multiple linear regression analysis indicated that the POST-race Asymmetry Index (AI) of navicular height was significantly predicted by the PRE-race AI of navicular height; navicular height displacement was predicted by PRE-race navicular height and the marathon time. Full marathon running induced increasing asymmetry and lowering of the medial longitudinal arch in runners.

INTRODUCTION: Maintaining flexibility, often defined as range of motion (ROM), is important. Recently, self-massage using a foam roller (FR) has been used in clinical and/or sports settings to effectively and immediately improve ROM. Many studies have found significant increases in ROM following the FR intervention; however, the mechanism of the effect is unclear. We aimed to clarify this mechanism regarding the ROM effects following the FR intervention by evaluating local tissue and autonomic nervous system responses. METHOD: The study employed a crossover design that included a comparison between non-intervention (CON trial: left leg) and intervention (FR trial: right leg) groups. Fourteen volunteers participated. Nine outcomes (passive maximum ankle ROM [ROM with a specified and non-specified passive strength], tissue hardness, skin temperature, water contents, circumference, blood flow velocity, pressure pain threshold, autonomic nervous system, and heart rate) were investigated before (PRE) and 0 min (POST0), 20 min (POST20), 40 min (POST40), and 60 min (POST60) post intervention. RESULTS: Skin temperature, impedance, and circumference changed significantly following the intervention, and increased ROM with non-specified strength was observed. DISCUSSION: Although we found that the FR intervention influenced skin temperature, impedance, circumference, and ROM, adaptability to the intervention may differ depending on an individual's characteristics. Females and/or individuals with a high body water content could obtain greater positive ROM effects than males and/or individuals with a low body water content. CONCLUSION: These findings suggest that the FR intervention may be an effective method to improve ROM, with alterations of skin temperature, impedance, and circumference.

Although a 3- to 7-min re-warm up (RW) elicits performance and physiological benefits after half-time (HT), a time-efficient and feasible RW protocol is required for the use of an RW in the athletic setting. This study aimed to investigate the effect of a 1-min RW at high-intensity on the performance and physiological responses during the Loughborough Intermittent Shuttle Test (LIST). In a randomized and counterbalanced cross-over design, 12 male amateur intermittent team sports players (soccer, basketball, handball, and lacrosse; age, 22 ± 2 years; height, 1.70 ± 0.08 m; body mass, 65.1 ± 8.3 kg; body mass index, 22.4 ± 1.9 kg m-2; VO2max, 53.5 ± 4.5 ml kg-1 min-1) performed the LIST. The LIST comprised two 45-min halves separated by a 15-min HT. Each half comprised repetitions of exercise cycles consisting of 3 × 20-m walking, 1 × 20-m maximal sprint, 3 × 20-m jogging, and 3 × 20-m running. During the HT, the participants were assigned to a control trial (CON; 15-min seated rest) or an RW trial (1-min running at 90% of the maximal oxygen uptake after a 14-min seated rest). Compared to the CON, the RW prevents reductions in sprint performance at the fourth and sixth periods of the LIST (fourth: 2.4%, p = 0.002, d = 1.68, sixth: 3.6%, p = 0.012, d = 1.74) and a decrement of gastrointestinal temperature during HT (0.5°C, p = 0.010, d = 1.41). Moreover, the RW decreased the electromyogram amplitude of maximal voluntary contraction (MVC) after HT (12%, p = 0.017, d = 1.12) without a decrease of maximal voluntary contraction force, suggesting an increased neuromuscular efficiency (9%, p = 0.048, d = 0.58). The RW also increased the mean heart rate in the initial part of the second half (4 bpm, p = 0.016, d = 0.38). In conclusion, the RW improved sprint performance, core temperature, muscle activation, and heart rate in the second half of the LIST. The findings suggest that the RW should be recommended for intermittent team sports players when longer RWs are not possible.

OBJECTIVE: This study aimed to compare the effect of different density foam rollers on range of motion recovery. METHOD: Ten active men completed two, 3-day trials in random order. During the experimental trials, all participants performed 2 min of foam rolling (FR) using a medium-density (medium trial) or hard-density (hard trial) foam roller on the right posterior thigh after completing the 90-min Loughborough Intermittent Shuttle Test (LIST). The hip joint range of motion (ROM), muscle hardness, and muscle soreness were assessed before and after the LIST and at 0 min, 20 min, 60 min, 24 h, and 48 h after FR intervention. Serum creatine kinase (CK) concentrations were assessed before the LIST and at 60 min, 24 h, and 48 h after FR intervention. The contralateral leg in each trial was used as a control. RESULTS: The ROM at 0 min, 20 min, 60 min, 24 h, and 48 h after FR intervention were higher in the right leg (the massage leg) than in the left leg (the contralateral leg) (p < 0.05). In the right leg, the ROM at 0 min after FR intervention was higher than after the LIST (p < 0.05). There were no significant differences between the medium and hard trials for ROM. Muscle hardness, muscle soreness, and serum CK concentration were not affected by FR. CONCLUSION: FR has a positive effect on ROM recovery. Moreover, the two roller densities provided similar ROM recovery.

CONTEXT: Several studies have reported that self-massage using a foam roller (FR) increased joint range of motion (ROM) immediately. However, the mechanism of increasing ROM by the FR intervention has not been elucidated. OBJECTIVE: To clarify the mechanism by investigating properties and morphological changes of muscles targeted by the FR intervention. DESIGN: An interventional study. SETTING: An athletic training laboratory. PARTICIPANTS: Ten male college volunteers with no injuries in their lower limbs (mean [SD]: age 23.8 [3.2] y, height 173.2 [4.9] cm, weight 69.5 [8.6] kg). INTERVENTION: The FR intervention on the right plantar flexors for 3 minutes. MAIN OUTCOME MEASURES: Maximum ankle ROM, muscle hardness, and fascicle length of the gastrocnemius muscle at the neutral (0°), maximum dorsiflexion, and maximum plantar flexion positions. All measurements were conducted before (PRE) and after (POST) the FR intervention. RESULTS: Dorsiflexion ROM increased significantly at POST (PRE: 13.6° [8.0°], POST: 16.6° [8.4°]; P < .001), although plantar flexion ROM did not change significantly between PRE and POST (PRE: 40.0° [6.1°], POST: 41.1° [4.9°]). There was no significant difference in muscle hardness and fascicle length between PRE and POST in any of the angles. CONCLUSIONS: Dorsiflexion ROM increased significantly by the FR intervention in the present study; however, muscle hardness and fascicle length did not change. FR may affect not only the muscle but also the fascia, tendon, and muscle-tendon unit. The FR protocol of the present study can be applied in clinical situations, because it was found to be effective to increase ROM.

OBJECTIVE: To assess the discriminability as well as the reliability, and internal consistency of the Identification of Functional Ankle Instability questionnaire translated into Japanese (IdFAI-J). DESIGN: Cross-sectional study. SETTING: Collegiate athletic training/sports medicine clinic. PARTICIPANTS: Twenty bilingual and sixty-five collegiate athletes including participants with and without functional instability (FI). MAIN OUTCOME MEASURES: The sensitivity, specificity, test retest reliability, and internal consistency of IdFAI-J. RESULTS: The optimal cutoff score between the FI and non-FI participants was >10, with an area under the curve of 0.92. We calculated high sensitivity (0.94) and specificity (0.77) at the cutoff point. For the test-retest reliability, the intraclass correlation coefficient value of the IdFAI-J was 0.96; the standard error of measurement and minimal detectable change value was 1.69 and 3.60, respectively. Cronbach's α was 0.87; there was no improvement when a particular item was deleted from the scale. CONCLUSIONS: The IdFAI-J has excellent discriminability, test-retest reliability, and internal consistency. Hence, the IdFAI-J significantly contribute to clinical practice and future research related to ankle instability in Japan.