Journal of Strength and Conditioning Research最新文献

Abstract: Yanaka, T, Imawaka, T, Kojima, C, Otomo, M, Ohnishi, T, and Hoshikawa, M. Evaluation of trunk oblique muscle activities in baseball batters using T2-weighted magnetic resonance imaging. J Strength Cond Res 39(1): 48-53, 2025-This study investigated abdominal oblique muscle activity using T2-weighted imaging in baseball batting. For this purpose, 17 baseball batters (21.6 ± 2.7 years, 173.9 ± 4.0 cm, 77.5 ± 7.6 kg) performed 100 toss-batting trials. Before and after toss-batting, 3 Tesla magnetic resonance imaging scans were performed to obtain the T2 values of the 4 abdominal external and internal oblique muscle pairs. The results showed that the T2 values of all abdominal oblique muscles were significantly increased after the 100 trials ( p < 0.05), with no differences in these increases between the muscles. The rate of change in the T2 values was 1.0 ± 3.9% and 4.2 ± 5.2% for the external and internal oblique muscles on the pitcher's side and 3.2 ± 5.1% and 0.9 ± 2.5% for the external and internal oblique muscles on the catcher's side, respectively. These findings indicate that the activity levels of all abdominal oblique muscles during baseball battings are similar and lower than those of the agonist muscles used during resistance exercise and sprinting. These findings suggest that baseball batting is a low-intensity exercise of the abdominal oblique muscles, but adequate training of each abdominal oblique muscle may improve batting performance and prevent injury.

Abstract: Yang, Y-R, Chen, C, Pan, C-H, Yen, S-Y, and Cheng, C-F. Effects of half-time re-warm-up with core strength exercises on subsequent agility and power performance in basketball players. J Strength Cond Res 39(1): 62-69, 2025-This study investigated the effects of half-time re-warm-up (RW) comprising core strength exercise (CSE) on basketball players' subsequent power and change of direction (COD) performance. Twelve male collegiate basketball players were recruited to perform 3 conditions--CSE RW on a stable platform (STA) or an unstable platform (USTA) and passive rest (control, CON)--in randomized, counter-balanced order after a modified Loughborough intermittent shuttle test (LIST). The COD and power performance tests were administered before the LIST and after the interventions. Heart rate (HR) was continuously measured during each trial. Results showed significantly lower changes in T-test time in STA compared with CON (p < 0.05). Changes in countermovement jump height in STA were significantly higher than those in CON (p < 0.05). During the isometric midthigh pull test, changes in the maximum rate of force development (RFD) (p < 0.05), RFD in the range of 0-90 milliseconds (p < 0.05), 0-150 milliseconds (p < 0.05), 0-200 milliseconds (p < 0.05), and 0-250 milliseconds (p < 0.05), in STA were significantly higher than those in CON. In addition, RFD in the range of 0-150 milliseconds (p < 0.05) and 0-250 milliseconds (p < 0.05) in USTA was significantly higher than that in CON. The mean HR during USTA was significantly higher than that in STA and CON (p < 0.05). These findings indicated that CSE RW during halftime might prevent power and COD performance decline in the second half of a game, with practical implications for coaches and players.

Abstract: Jiang, G, Tan, X, Zou, J, and Wu, X. A 24-week combined resistance and balance training program improves physical function in older adults: a randomized controlled trial. J Strength Cond Res 39(1): e62-e69, 2025-This randomized controlled trial assessed the feasibility of older adults performing combined resistance and balance training (RBT) and compared the effects of RBT on physical function with those of resistance training (RT) alone and with no exercise training in older adults. In total, 65 community-dwelling adults aged 60-74 years were randomly assigned to an RT (n = 22), RBT (n = 22), or control (n = 21) group. The exercise intervention consisted of RT or RBT for 45 minutes, 3 times per week for 24 weeks. The control group engaged in no exercise training. The compliance rates were 93% in the RT group and 92% in the RBT group. No training-related adverse effect was observed. In the RT and RBT groups, dynamic balance (p = 0.017; p < 0.001, respectively), maximum walking speed (p = 0.014; p < 0.001), upper extremity (p = 0.013; p = 0.009) and lower extremity (p = 0.009; p < 0.001) muscle strength, and spirometry (p = 0.043; p = 0.018) were significantly improved at 24 weeks compared with the control group. Only the RBT group showed significant improvement in normal walking speed (p = 0.002). Compared with the RT group, the RBT group showed additional significant improvements in dynamic balance (p = 0.001) and lower limb muscle strength (p = 0.027). The findings of this randomized controlled trial indicated that RBT was safe and feasible for older adults. Long-term RBT had better effects than either no exercise training or RT alone on improving physical function in older adults. Compared with RT, RBT additionally benefited dynamic balance and lower limb muscle function, which are clinically important factors in preventing falls, frailty, disability, and other geriatric syndromes.

Abstract: Dennison, L, Duthie, GM, Ehrmann, F, and Psarakis, MA. Concurrent validity and interunit reliability of 25-Hz GNSS units for profiling sprinting performance. J Strength Cond Res 39(1): 107-114, 2025-Profiling sprint performance by assessing within-race velocity or time is crucial for understanding an athlete's capabilities and identifying areas for improvement. While traditional gold standard systems provide valid and reliable measurements, they are often costly, laboratory-based, or impractical for field-based settings. New Global Navigation Satellite System (GNSS) units (25 Hz) with higher sampling rates may address some of these limitations. The purpose of the project was to evaluate the concurrent validity and interunit reliability of 25-Hz GNSS units by examining their agreement with laser devices and timing gates for velocity measurements and sprint/interval times. Concurrent validity was assessed during a real track and field training session. Thirty subjects each completed 3 to 6 maximal 40-meter sprints, for a total of 106 sprints, while being assessed simultaneously through all systems. Interunit reliability was assessed by placing 3 GNSS units on a motor vehicle and completing 60 accelerations from 0 to 60 m. Low mean bias (<1%) and typical error less than <2% for all measurements demonstrate excellent agreement between GNSS and criterion devices. The units demonstrated good reliability for the 0-10 m interval time (intraclass correlation coefficient [ICC] = 0.86), excellent reliability for all remaining 10 m to 60 m intervals (ICC = 0.91-0.99), sprint times 0-60 m (ICC = 0.97), and maximal sprint velocity (ICC = 1.0). These GNSS units provide an efficient and feasible alternative to traditional measurement devices. For coaches, this technology offers a scalable method to concurrently assess the sprint performances of multiple athletes during training and competitions, enabling evidence-based decisions to guide athletic development.

Abstract: Larsen, S, Zee, Md, and Tillaar, Rvd. The impact of stance width on kinematics and kinetics during maximum back squats. J Strength Cond Res 39(1): 1-9, 2025-This study compared the lower extremity peak net joint moments (NJMs) and muscle forces between wide and narrow stance widths defined as 1.7 and 0.7 acromion width in the last repetition of the concentric phase in 3 repetition maximum back squats. Twelve recreationally trained men (age:25.3 ± 2.9 years, height:179 ± 7.7 cm, body mass:82.8 ± 6.9 kg) volunteered for the study. The NJMs were estimated using inverse dynamics and individual muscle forces with static optimization. The main findings of interest were that the wide stance resulted in statistically smaller knee flexion angles (Cohen's d: 0.9; 95% confidence interval [CI]: -17.96 to -3.18°), knee extension NJMs [d: 1.45; 95% CI: -1.56 to -0.61 Nm·kg-1], and vastii forces [d: 1.3; 95% CI: -27.7 to -0.9.5 N·kg-1] compared with the narrow stance. Moreover, we observed significantly larger hip abduction angles [d: 3.8; 95% CI: 12.04 to 16.86°] for the wide stance. Hence, we suggest that recreationally trained men aiming to optimize muscle forces in the vastii muscles during maximum back squat training should consider adopting a narrow stance.

Abstract: Favro, F, Roma, E, Gobbo, S, Bullo, V, Di Blasio, A, Cugusi, L, and Bergamin, M. The influence of resistance training on joint flexibility in healthy adults: A systematic review, meta-analysis, and meta-regression. J Strength Cond Res XX(X): 000-000, 2024-Joint flexibility is a key component of physical fitness. Despite the large body of evidence regarding the effectiveness of muscle stretching exercises, little is known about the effect of resistance training on flexibility. A systematic search was conducted on 9 academic search instruments; inclusion criteria were as follows: healthy adult participants (age ≥18 years); resistance training intervention (duration ≥4 weeks); at least one flexibility outcome. Risk of bias was assessed using the RoB-2 and ROBINS-I tools. A 3-level meta-analysis was conducted, with multiple outcomes nested within each study. A moderator analysis was conducted by fitting a meta-regression model. Significance level was set at p < 0.05. We included 36 studies (1,469 participants). None of the included papers resulted at a low risk of bias. The pooled effect size for resistance training on flexibility was g = 0.6325, with 95% CI: 0.4762 to 0.7888 (p < 0.0001). There was a substantial amount of heterogeneity between studies. Exercise intensity was a significant moderator (p < 0.0225, high vs low), based on 129 and unique effect sizes, and sex (p = 0.0429). Activity level and age were nonsignificant moderators. Resistance training could be implemented as a strategy to improve joint flexibility, with high-intensity protocols resulting in a magnified effect. However, the high overall risk of bias and substantial heterogeneity limit our ability to draw definitive conclusions.

Abstract: Somma, M and Lawrence, MA. Reliability and accuracy of Stryd to detect changes in vertical displacement of the center of mass while running. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to determine if Stryd can reliably and accurately detect changes in vertical displacement of the center of mass (VCoM) that are produced when cadence was increased by 5 and 10%. A secondary purpose of this investigation was to determine the interlimb reliability of Stryd for VCoM and cadence. Twenty healthy individuals (5 males, 15 females; age: 24.5 ± 1.5 years; mass: 67.1 ± 12.2 kg; height: 1.66 ± 0.01 m) were fitted for motion capture and 2 Stryd devices. After warm-up, subjects ran at a self-selected speed on the treadmill for each condition (self-selected, +5%, and +10% cadence) while VCoM and cadence were collected simultaneously from Stryd and motion capture. Reliability between the Stryd devices on different limbs was excellent for both cadence (intraclass correlation coefficient [ICC] = 0.999, p < 0.001) and VCoM (ICC = 0.993, p < 0.001). Cadence was not significantly different between the Stryd device and motion capture (p = 0.153). Stryd produced significantly (p < 0.001) smaller values for VCoM regardless of condition, with average differences ranging between 4.4 and 4.6 cm. A linear regression revealed that Stryd predicted 50.7% of variation in motion capture VCoM (p < 0.001). Stryd can reliably measure both cadence and VCoM regardless of which limb it is placed on, as indicated by the near-perfect agreement between Stryd devices, and the Stryd device can detect and predict changes in VCoM. However, Stryd consistently underestimates VCoM, which can be corrected by using a linear regression equation.

Abstract: Lockie, RG, Young, MA, Lanham, SN, Orr, RM, Dawes, JJ, and Nagel, TR. Scenario and shooting performance in incumbent deputy sheriffs/police officers, cadets, and cadets who worked in custody/corrections facilities. J Strength Cond Res XX(X): 000-000, 2024-Job-specific fitness of law enforcement personnel can decline during their careers. Personnel could offset fitness deficiencies with greater skill and knowledge. Cadets in certain counties may work in custody/corrections before their training academy. This study used archival data to compare job-specific scenario performance of incumbent deputy sheriffs/police officers (INC; n = 15), cadets entering academy (CAD; n = 19), and cadets entering academy after working in custody/corrections facilities (CADCUST; n = 25). Subjects completed a scenario (step-ups, jumping jacks, sprawls, strikes, drags, sandbag carries, and a simulated fight) as fast as possible followed by a firearms test where they had to hit 6 steel plates. Steel time (time to hit all plates) and number of shots required were recorded. Univariate analysis of covariances, with sex and age as covariates and Bonferroni post hoc analyses, derived between-group differences in all variables (p < 0.05). The CAD group completed the scenario faster than the INC group (p = 0.011). Though not significant, the INC group did have the fastest steel time and lowest number of shots. The CADCUST group completed the scenario 10% slower than the CAD group, was 138-366% slower in steel time, and needed 61-100% more shots than the other groups. The INC group likely had fitness limitations that affected scenario performance but demonstrated better shooting skills. The CADCUST group was slower than the CAD group in the scenario and performed worst in the shooting test. Cadets who work in custody/corrections facilities before academy may require fitness and skill interventions while INC should attempt to maintain their fitness during their career.

Abstract: Cornejo-Daza, PJ, Sánchez-Valdepeñas, J, Páez-Maldonado, J, Rodiles-Guerrero, L, Sánchez-Moreno, M, Gómez-Guerrero, G, León-Prados, JA, and Pareja-Blanco, F. Acute responses to different lifting velocities during squat training with and without blood flow restriction. J Strength Cond Res XX(X): 000-000, 2024-The aims of the research were to compare the acute mechanical, metabolic, neuromuscular, and muscle mechanical responses to different lifting velocities (maximal vs. half-maximal) under distinct blood flow conditions (free [FF] vs. restricted [BFR]) in full-squat (SQ). Twenty resistance-trained males performed 4 protocols that differed in the velocity at which loads were lifted (MaxV: maximal velocity vs. HalfV: half-maximal velocity) and in the blood flow condition (FF: free-flow vs. BFR: 50% of arterial occlusion pressure). The relative intensity (60% 1 repetition maximum), volume (3 sets of 8 repetitions), and resting time (2 minutes) were matched between protocols. Mean propulsive force (MPF), mean propulsive velocity (MPV), mean propulsive power (MPP), and electromyography (EMG) values were recorded for each repetition. Tensiomyography (TMG), blood lactate, countermovement jump (CMJ), maximal voluntary isometric contraction in 90° SQ, and performance with the load that elicited a 1-m·s-1 velocity at baseline measurements (V1-load) in SQ were assessed at pre-exercise and postexercise. The MaxV protocols showed significantly greater MPF, MPV, MPP, and EMG amplitude during the exercise than the HalfV protocols (velocity effect, p < 0.05). The FF protocols achieved higher MPF and MPP during exercise than BFR (BFR effect, p < 0.05). The BFR protocols induced greater blood lactate after exercise (BFR × time interaction, p = 0.02), along with higher postexercise impairments in mechanical performance (BFR × time interaction, p < 0.05). The MaxV protocols elicited superior performance and greater muscle activation during exercise. The BFR protocols resulted in lower force and power production during exercise and exhibited higher performance impairments and increased metabolic stress postexercise.

Abstract: Rebelo, A, Loturco, I, Pereira, JR, Martinho, DV, Valente-dos-Santos, J, and Broek, GV. Impact of congested match schedules on countermovement jump metrics in elite volleyball players. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to assess the impact of a congested match schedule on various countermovement jump (CMJ) metrics recorded across the braking, transfer, propulsive, and flight phases of the CMJ. Fourteen male elite volleyball players were monitored across 7 microcycles, with CMJ assessments conducted at 14 time points using portable force plates. Repeated measures analysis of variance with Bonferroni post hoc tests and coefficient of variation (CV) analysis were used to analyze the data. The CVs for all metrics indicated a moderate variability between microcycles and low variability between the beginning and end of the weeks. Significant variability was observed in key performance metrics, including peak propulsive power (p < 0.001, partial eta squared [ηp2] = 0.336), peak propulsive velocity (p = 0.005, ηp2 = 0.207), propulsive phase duration (p = 0.008, ηp2 = 0.197), and jump momentum (p = 0.019, ηp2 = 0.225), across microcycles. These findings indicate that these CMJ metrics may be used as sensitive indicators of fatigue and performance changes during intense training and competitive periods. The total score of athleticism, calculated by averaging a set of standardized scores from multiple tests or repeated measures of the same test, for the propulsive and flight phases, proved to be particularly useful in providing a comprehensive view of the neuromuscular status. This emphasizes the importance of recording and analyzing a range of CMJ metrics to optimize training and recovery strategies in elite volleyball players.