Journal of Strength and Conditioning Research最新文献

Abstract: Montalvo, S, Gonzalez, MP, Dietze-Hermosa, MS, Martinez, A, Rodriguez, S, Gomez, M, Ibarra-Mejia, G, Tan, E, and Dorgo, S. Effects of different stretching modalities on the antagonist and agonist muscles on isokinetic strength and vertical jump performance in young men. J Strength Cond Res 39(2): 173-183, 2025-Exercise warm-up may include static or dynamic stretching, impacting performance differently. This study investigated the effects of various stretching protocols on isokinetic strength, muscular activity, and vertical jump performance. Sixteen subjects, divided evenly between trained and untrained groups, underwent 8 distinct stretching conditions in random order. Outcomes measured included isokinetic knee extension and flexion torque and power, muscular activity (vastus lateralis, vastus medialis, and biceps femoris), and jump performance (jump height and modified reactive strength index [RSImod]). Responses to the stretching conditions were analyzed using a mixed-methods approach. For isokinetic knee extension, dynamic stretching of both agonist and antagonist (DY-AG-ANT) and combined dynamic agonist with static antagonist stretching (DY-AG ST-ANT) produced significant improvements. Dynamic stretching of both agonist and antagonist increased peak torque by 12.72% and average torque by 30.80%, while DY-AG ST-ANT increased peak torque by 15.61% and average torque by 41.06%. Muscular activity also improved significantly; DY-AG ST-ANT increased EMG activity of the vastus lateralis by 29.43% and vastus medialis by 70.75%. Biceps femoris saw a 33.18% increase with DY-AG and a 22.15% increase with ST-AG. Countermovement jump height improved with DY-AG-ANT (12.6%) and static antagonist (ST-ANT) conditions (11.3%) ( p < 0.05). Dynamic stretching of both agonist and antagonist also enhanced average power knee extension by 32.41%, while ST-AG DY-ANT improved it by 31.09% ( p < 0.05). Dynamic stretching, especially when combined with static stretching, optimizes isokinetic strength, muscular activity, and jump height. Coaches should incorporate dynamic stretching, alone or with static antagonist stretching, to maximize performance.

Abstract: Talpey, SW, Drake, M, Haintz, L, Belanger, A, O'Grady, MW, Young, WB, Mundy, PD, James L, Gabbett, TJ, Gardner, EC. The reliability and validity of the rebound countermovement jump in National Collegiate Athletic Association Division I American football players. J Strength Cond Res 39(2): 200-209, 2025-The purpose of this study was to investigate the reliability and validity of the rebound countermovement jump (R-CMJ), as an alternate test of leg muscle function to the CMJ and drop jumps (DJs). Because the first phase of the R-CMJ mimics that of the CMJ, it is hypothesized that variables obtained in phase I of the R-CMJ will be like those of a CMJ. Similarly, because the second phase of a R-CMJ mimics a DJ, it is believed that the variables obtained from phase II will be like those from a DJ. Collegiate male American football players ( N = 46) aged 18-24 years completed CMJs and R-CMJs on a portable force plate. Tests were completed on 3 separate days to determine the repeatability of select variables and to establish their validity. In addition, a subgroup ( N = 20) of players from the cohort completed DJs from both 30 cm (DJ30) and 45 cm (DJ45) to determine the concurrent validity of the variables obtained from the second phase of the R-CMJ. Most variables obtained from the CMJ and R-CMJ phase I were found to be reliable, except for time-to-take-off. The variables from the DJ30, DJ45, and R-CMJ phase II displayed moderate to good reliability; however, all coefficient of variations were >10%. Jump height achieved in the CMJ was significantly greater than that achieved in phase I of the R-CMJ. The reactive strength index was significantly different in the R-CMJ compared with the DJ from both 30 and 45 cm heights. Although the R-CMJ may be inviting for coaches to use owing to its ease and time efficiency, the results of this study highlight that it may not provide a valid representation of an athlete's reactive strength.

Abstract: Mangine, GT, Hines, A, Grazer, J, Esmat, TA, and McLester, J. Can video annotation software with minimal standardization be used as a back-up for a marker-free motion tracking system when monitoring barbell thruster velocity during a repeated circuit? J Strength Cond Res 39(2): 147-155, 2025-This study examined the agreement between a marker-free motion tracking system (PERCH) and a free video annotation software (KINOVEA) for measuring barbell thruster velocity using minimal standardization. For a larger placebo-controlled supplement intervention, 10 men (28.7 ± 8.0 years, 175 ± 8 cm, 91.0 ± 12.0 kg) and 10 women (31.3 ± 5.2 years, 167 ± 4 cm, 70 ± 13 kg) completed a circuit of rowing, 6 barbell thrusters (men: 43.1 kg, women: 29.5 kg), and 3 box jumps for "as many repetitions as possible" (AMRAP) in either 5 or 15 minutes. Barbell velocity (m × second -1 ) was monitored by PERCH from the frontal plane, whereas all sessions were video recorded from the same view and subsequently analyzed by KINOVEA using natural barbell landmarks. Fifty repetitions were randomly and equally drawn from each participant ( n = 1,000 repetitions) across all workout and supplement conditions. Although Wilcoxon signed-rank test revealed no differences (mean difference = 0.03 m × second -1 , p = 0.332), KINOVEA only explained 2.6% of PERCH variance, and Spearman's correlation analysis of Bland-Altman plots suggested that differences between technologies were exacerbated by the magnitude of velocity ( ρ = -0.62, p < 0.001). Cross-validated, regression analysis using KINOVEA and readily available participant demographics (arm reach and biological sex) improved prediction by 13.4% but agreement remained inconsistent ( ρ = 0.73, p < 0.001). Neither KINOVEA nor KINOVEA combined with participant demographics are interchangeable with PERCH for monitoring barbell velocity during an AMRAP. Still, researchers and athletes might use this free and accessible software as back-up for whenever PERCH fails to detect repetitions, as some information is better than none.

Abstract: Roberts, TD, Smith, RW, Arnett, JE, Ortega, DG, Schmidt, RJ, and Housh, TJ. Cross-validation of equations for estimating 1 repetition maximum from repetitions to failure for the bench press and leg extension. J Strength Cond Res 39(2): e96-e105, 2025-Eighteen previously published equations (EQs) that estimate 1 repetition maximum (1RM) from repetitions to failure (RTF) were cross-validated for the bench press (BP) and leg extension (LE) movements. Forty-three recreationally active men (age: 20.58 ± 1.47 years; body mass [BM]: 81.66 ± 13.65 kg) completed a 1RM test and RTF at 80% of the 1RM test for the LE, and 39 of the 43 men (age: 20.61 ± 1.48 years; BM: 83.58 ± 12.73 kg) completed the same tests for the BP. The EQs were categorized as generic (the source did not indicate its applicability for a specific movement) or movement-specific (BP-specific and LE-specific EQs). The generic EQs were cross-validated for both movements, whereas the BP-specific and LE-specific EQs were cross-validated for their respective movements only. The cross-validation criteria included calculations of the constant error (CE) (mean differences between estimated and measured 1RM), Pearson Correlation Coefficient, standard error of the estimate, and total error. The level of significance was set at p ≤ 0.05. After the initial cross-validation analyses of the previously published EQs, the most accurate EQs were modified by subtracting their cross-validation CE from the original EQ to improve their accuracy for estimating BP and LE 1RM by eliminating systematic error. The modified EQs were then cross-validated using the same statistical procedures. Based on the cross-validation analyses, we recommend the following EQs: BP 1RM = (RTF 0.1 × weight) + 1.49 and LE 1RM = (RTF 0.1 × weight) + 1.06 using weights that result in 4-10 RTF.

Abstract: Gries, KJ and Witto, PE. Age and sex differences in IRONMAN world championship performance. J Strength Cond Res 39(2): 269-276, 2025-There has been an increasing number of masters athletes, particularly women, who have been competing in ultra-endurance events. With this in mind, we sought to determine the influence of age and sex on IRONMAN World Championship performances from 2014 to 2023. The final times of each component (swim, bike, and run) and overall time were collected for places 1st to 10th in each age group (18-69 years). Sex differences in performance were calculated for each age group. Depth of field (time of n th place/first place), a surrogate for participation, was also calculated for each age group and sex. Significance was set at p < 0.05. These data show a ∼12% sex difference in the performance of the swim, bike, run, and final ( p < 0.05), which increased to 20% in the 65-69 years age group ( p < 0.05). The differences appeared driven by the bike and run. Depth of field was greater in men than in women ( p < 0.05), and the sex difference increased with age. Sex differences in performance trended to be related to depth of field ( p = 0.08; R2 = 0.32), suggesting a moderate role of participation in performance sex differences. Although speculative, the performance data can give us an insight into the physiology and sociology of these elite athletes and warrants future research.

Abstract: Hsu, SM, Tseng, WC, Chiu, CH, Hsieh, TY, Weng, MC, Dai, X, and Chen, CH. Effects of preconditioning lower-extremity resistance exercises on multi directional repeated sprinting-induced muscle damage. J Strength Cond Res 39(2): e89-e95, 2025-Sprint exercise-induced muscle damage is a popular area of investigation. To examine whether preconditioning lower-extremity resistance exercises would reduce the amount of muscle damage observed after a multi-directional repeated sprinting (MDS) exercise. Thirty-six elite male athletes were randomly allocated to 1 of 3 groups: general warm-up (GW), GW with loaded jump squat (SQ), and GW with loaded hip thrust (HT). Knee flexion isometric strength (MVIC), passive hip flexion range of motion (ROM), soreness, countermovement jump (CMJ), sprint time, and plasma creatine kinase (CK) activity were measured at the pretest and post-24, -48, and -72 hours of the MDS. For SQ, the CK at post-72 hours was significantly lower than the GW group. The decrements of MVIC at post-48 and -72 hours for SQ were significantly less than the GW group. The CMJs at post-24 and -48 hours for SQ and at post-48 and -72 hours for HT were significantly higher than the GW group. The 0-10 m sprint time at post-48 hour for HT was significantly better than the GW group. Adding the SQ or HT interventions to a GW before MDS has a protective effect on the sprinting-induced muscle damage and faster recovery.

Abstract: Comstock, BA, Flanagan, SD, Denegar, CR, Newton, RU, Häkkinen, K, Volek, JS, Maresh, CM, Kraemer, WJ. Structural and functional properties of lower extremity tendons in men. J Strength Cond Res 39(2): 184-191, 2025-The purpose of this study was to understand further patellar and Achilles tendon structure and function, body composition, and serum collagen turnover biomarkers in young men who performed heavy resistance training (RT, n = 13, age: 22.2 ± 1.4 years) compared with recreationally active men who were not resistance-trained (NR, n = 13, age: 22.8 ± 2.2 years). Tendon properties were measured at rest and during maximal voluntary isometric efforts using ultrasonography and dynamometry. Lean body mass (LBM) and bone mineral density (BMD) were assessed with dual X-ray absorptiometry. Serum collagen turnover markers were analyzed and related to tendon measures. Resistance-trained men had significantly ( p ≤ 0.05) greater LBM and BMD compared with recreationally active men. Resistance-trained men also showed significantly greater patellar tendon (PT) stiffness (45%) and Young's modulus (36%), though the PT cross-sectional area (CSA) did not differ significantly between groups. Achilles tendon CSA was significantly larger in resistance-trained men. Still, other properties such as stiffness and modulus did not differ significantly between the groups. Serum collagen turnover markers showed no significant differences between groups and were not correlated to any tendon or bone biomarkers. The findings support that resistance-trained men have greater LBM and BMD. However now, it reveals that tendon adaptations differ, as not all measures were similarly affected in both tendons. The blood biomarkers did not show any obvious roles in explaining the differential changes in tendons. Heavy RT induces differential tendon changes potentially due to complex interactions of training variables.

Abstract: Riboli, A, Nardi, F, Osti, M, Cefis, M, Tesoro, G, and Mazzoni, S. Training load, official match locomotor demand, and their association in top-class soccer players during a full competitive season. J Strength Cond Res 39(2): 249-259, 2025-To examine training load and official match locomotor demands of top-class soccer players during a full competitive season and to evaluate their association. Twenty-five top-class soccer players competing in UEFA international competitions were included. The season was divided into 2 different categories: 2 matches (M2) or 3 matches (M3) in 8 days. Starters and nonstarters were classified. Total distance (TD), high-speed running (HSR, 15-20 km·h-1), very high-speed running (VHSR, 20.1-24 km·h-1), sprint (SPR, >24.1 km·h-1), and accelerations/decelerations (Acc + Dec, >3 m·s2) were recorded. Trivial to moderate differences (p < 0.05) in training load between M2 and M3 were found: HSR, VHSR, and SPR were higher in M2 than M3, whereas TD and Acc + Dec were higher in M3 than M2. Week-by-week variability in training load ranged from ∼16 to ∼59% depending on metrics. Official match locomotor demands were similar (p > 0.05) in M2 and M3 with ∼5 to ∼29% match-to-match variability depending on metrics. Total load (i.e., training plus match loads) was higher (p < 0.05, ES: 0.75/1.61) in starters than nonstarters, because of a higher match load and no difference in the training load. Very high-speed running and SPR accumulated during training sessions were largely to very largely (r = 0.60 to 0.72) associated with TD, HSR, VHSR, and Acc + Dec covered during official match; VHSR and TD during training were largely to very largely (r = 0.57 and 0.71) associated with SPR and Acc + Dec during official match. In conclusion, (a) congested periods seemed to not affect official match locomotor performance; (b) practitioners may consider high week-by-week workload variability for individualizing training prescriptions, especially for nonstarters; and (c) the VHSR and SPR accumulated during training were associated with the official match locomotor demands, and it may be considered for maximizing performance.

Russell, JL, Baker, BS, Mercer, RA, and McLean, BD. Examining the influence of season phase, age, and anthropometrics on body composition trends in NBA athletes. J Strength Cond Res 39(2): 227-233, 2025-This study aimed to describe seasonal body composition changes in NBA athletes using Dual-energy X-ray Absorptiometry (DXA) and to explore the relationship between these changes and factors such as age and anthropometrics. A retrospective analysis was conducted using 402 DXA scans from 62 professional male basketball players, obtained from one NBA team between 2012 and 2023. Seasonal phases were defined as preseason, pre all-star, post all-star, and offseason. A custom region of interest (ROI) method was used to ensure consistent scan areas for taller athletes who exceeded the DXA bed length. Linear mixed models analyzed the influence of seasonal phases, age, and height on lean mass (LM), fat mass (FM), and bone mineral content (BMC). In-season phases (pre all-star and post all-star) showed small increases in LM and decreases in FM compared with the preseason, with no significant BMC changes. Chronological age was associated with increases in LM but not FM. Taller athletes exhibited increases in LM, FM, and BMC. Significant random variance across players and seasons indicated that additional unmeasured factors might influence body composition. NBA athletes generally gain LM and lose FM during the season, with older players showing increased LM gain. The study's novel ROI method provide reliable data for athletes exceeding standard DXA limits, highlighting the importance of tailored body composition assessments in professional basketball. These findings can inform strength and conditioning, nutrition, and player development strategies across different seasonal phases and ages.