Background/Objectives: In this study, we aimed to examine the effect of creatine monohydrate (CrM) supplementation on recovery from eccentric exercise-induced muscle damage (EIMD) in diverse populations, including different sexes and age groups. EIMD decreases maximal voluntary contraction (MVC), restricts the range of motion (ROM), and increases muscle stiffness and delayed-onset muscle soreness, all of which negatively impact athletic performance. Therefore, developing effective recovery strategies is essential. Methods: A double-blind, randomized, placebo-controlled trial was conducted with 40 healthy male and female participants. After 33 days of supplementation with either CrM or placebo (crystalline cellulose), the participants performed eccentric exercises. Recovery indices, including MVC, muscle stiffness, subjective muscle extensive soreness, fatigue, and upper arm circumference, were measured at baseline, immediately after exercise, 48 h post-exercise, and 96 h post-exercise. Results: The creatine supplementation group (CRE) demonstrated a significantly quicker recovery of MVC than the placebo group (PLA). Furthermore, reductions in shear modulus and muscle fatigue were observed in the CRE group. Notably, females in the CRE group exhibited a significant suppression of post-exercise edema, suggesting a sex-specific response. Conclusions: These findings indicate that CrM supplementation may enhance recovery from EIMD, contributing to the maintenance of muscle function and the reduction of discomfort after exercise. CrM has the potential to serve as a practical nutritional strategy to promote recovery, not only for athletes, but also for a broader population.

Purpose: The flight-time method (FT) is used for measuring vertical jump height (JH) in the field because of its convenience; however, FT overestimates JH when the lower limb is flexed at landing. Herein, we proposed a new method (ie, flight-time method modified [FTM]) to address the problem of FT and evaluate its validity and reliability. Methods: A total of 24 men performed 6 countermovement jumps on force plates (sampling rate: 1000 Hz) while being recorded with a smartphone high-speed camera at 240 frames·s^–1. JH was calculated by the impulse–momentum method (IM), FT, and FTM. For FTM, the flight time and JH were calculated based on the displacement of the greater-trochanter marker using a smartphone application. Results: JH calculated using FT was significantly higher (P < .001) compared with JH calculated by IM; however, JH calculated by FTM showed no significant difference with JH calculated by IM. Furthermore, JH calculated by FTM, compared with JH calculated by FT (ρ = .882; 95% CI, .838–.914), exhibited a stronger, nearly perfect, and significantly positive correlation (ρ = .987; 95% CI, .982–.991) with JH calculated by IM and showed high reliability. Conclusions: The FTM proposed in this study had higher concurrent validity compared with FT and a high reliability for measuring countermovement JH because it was not affected by lower-extremity flexion at landing. Therefore, practitioners should consider using FTM as a convenient, low-cost, reliable, and more valid method for measuring JH in the field.

The study aimed to investigate the relationships between the shear modulus of the biceps brachii (BB) and brachialis muscle (BA) and the total of the two (BB+BA), and urinary titin N-terminal fragment (UTF), maximum voluntary isometric contraction (MVC), and other indirect markers. Fifteen healthy men per-formed five sets of 10 eccentric contractions using a dumbbell corresponding to 50% of MVC at 90(degrees) measured at baseline. The elbow joint of the left arm was extended from 90(degrees) to 180(degrees) (180(degrees) = full extension) in 5 s in the exercise, and was returned with sup-port from the examiner to prevent concentric contraction. Shear modulus of BB and BA were measured by ultrasound shear wave elastography, and UTF, MVC, and range of motion of the elbow joint (ROM) were recorded before; immediately after; and 1, 24, 48, 72, 96, and 168 h after the exercise. After calculating the shear modulus of BB and BA, two values were added (BB+BA). The shear modulus peaked at 48 h, UTF peaked at 96 h, MVC and ROM changed largest at immediately, and muscle soreness peaked at 48 h post-exercise. Significant (p < 0.05) relationships were found between changes in BB shear modulus and BA shear modulus (r = 0.874), BB+BA shear modulus (r = 0.977), UTF (r = 0.681), and MVC (r = -0.538). Significant (p < 0.05) relation-ships were also observed between changes in BA shear modulus and BB+BA shear modulus (r = 0.957), UTF (r = 0.682), MVC (r = -0.522), and ROM (r = -0.600). Moreover, significant (p < 0.05) relationships were observed between changes in BB+BA shear modulus and UTF (r = 0.703), MVC (r = -0.549), and ROM (r = -0.547). These results indicate that shear modulus of each muscle (i.e., BB and BA) provide more precise information about muscle damage than UTF, MVC and ROM.

Relationships between Changes in Muscle Shear Modulus, Urinary Titin N- Terminal Fragment, and Maximum Voluntary Contraction Torque after Eccentric Exercise of the Elbow Flexors

Nishioka, T, Yamaguchi, S, Hajima, D, Yabuno, N, Aoki, A, Kunita, Y, Hashimoto, Y, and Inami, T. Validity and reliability of a novel timing gate system for real-time measurement of sprint force-velocity profile. J Strength Cond Res 40(7): e670–e675, 2026—The purpose of this study was to investigate the concurrent validity and intertrial reliability of a newly developed timing gate system, VoltOnoSprint (VOS), with a mat switch and smartphone app for real-time measurement of the sprint force-velocity (F-V) profile. Twenty-four men (age: 21.1 ± 2.1 years) performed two 30-m sprints. Subjects' body center of mass velocity and position-time data were measured simultaneously by radar and VOS, respectively, and were used to calculate the sprint F-V profile variables. All sprint F-V profile variables derived from VOS had significant, positive, and nearly perfect correlations ( r = 0.905 to 0.964) with radar measurements and did not differ significantly ( d = 0.073 to 0.110) from those derived from radar. The sprint F-V profile variables calculated using both systems exhibited acceptable intertrial reliability (intraclass correlation coefficient = 0.767 to 0.985, coefficient of variation = 0.88–4.81%), except for the relative reliability of one F-V profile variable (the slope of the F-V relationship) derived from radar. Furthermore, all sprint F-V profile variables derived from VOS had higher absolute variability than those derived from radar. These results suggest that VOS is a valid and reliable method for sprint F-V profiling, and the reliability of the sprint F-V profile variables measured by VOS was superior to that measured by radar, a criterion method. Therefore, VOS can be a valuable system for practitioners seeking real-time and accurate measurement of the sprint F-V profile.

Background/Objectives: Osgood–Schlatter disease (OSD) is a common overuse condition in adolescents characterized by increased stiffness of the rectus femoris muscle, which contributes to pain and functional limitations around the knee. We investigated whether repeating 10 min passive joint movements of the hip and knee produces additional immediate reductions in elevated rectus femoris (RF) stiffness in adolescents with OSD. Methods: Fifteen patients (10–14 years of age) diagnosed with bilateral OSD were included. The legs of the participants were randomly assigned to either the intervention or the non-intervention side (control). The intervention side received two sets of 10 min of passive joint movement to the hip and knee, while the control side rested. RF stiffness was measured before the intervention and immediately after one and two sets of passive joint movements. Results: On the intervention side, RF stiffness decreased significantly from pre to post-1 and from pre to post-2; however, RF stiffness did not differ significantly between post-1 and post-2. None of the parameters changed significantly on the control side (rest condition). Conclusions: Passive joint exercise beyond one repetition (one set for 10 min) did not result in a further decrease in RF stiffness and is likely unnecessary for RF muscle stiffness due to OSD.