Journal of Strength and Conditioning Research最新文献

Abstract: Chiba, Y, Sato, K, Yoshimoto, T, Ohnuma, H, Yamanaka, R, Takahashi, K, Kobayashi, K, Matsubayashi, T, and Takai, Y. Revamping pace distribution: A case study on elevating the men's 400 m track and field Japanese national record after 32 years. J Strength Cond Res XX(X): 000-000, 2024-Many studies have investigated the 400-m sprint, and the optimal pacing strategy is subject to debate. Little information is available regarding the effects of changes in the pacing strategy on running speed and spatiotemporal variables in the official 400-m race. This case study analyzed changes in running speed and spatiotemporal variables of a Japanese elite long sprinter who set a new Japanese national record in the 400-m race by modifying his pace distribution based on the analysis of his previous races and the performances of world-class long sprinters. To revamp his pace distribution, 25 preceding races (ranging from 45.47 to 46.95 seconds) were analyzed, spanning from June 2015 to June 2023. The independent variables were the 50-m split time, average running speed, percentage of the 50-m split time relative to the 400-m record, step length, and step frequency. K.S. broke his own record by modifying the pacing distribution based on the development of his previous race and the world-class long sprinters. The modified pacing strategy increased running speed in the 200- to 300-m section. Step lengths were longer throughout the 400 m, and step frequencies were higher in the last 200 m than before the alteration in the pace distribution. Modifying the pacing strategy from leading to driving may enhance the personal records of long sprinters. This improvement is attributed to the maintenance of longer step lengths over the entire 400-m range and an increase in the step frequency in the last 200 m.

Abstract: Şentürk, D, Akyildiz, Z, Janicijevic, D, and García-Ramos, A. Sensitivity of the load-velocity relationship variables to discriminate the level of fatigue induced by multiple sets of the hexagonal barbell deadlift exercise. J Strength Cond Res XX(X): 000-000, 2024-This study aimed to evaluate changes in load-velocity (L-V) relationship variables (L0, v0, and Aline) after different fatigue protocols and to determine their correlation with changes in 1 repetition maximum (1RM). After determining the hexagonal barbell deadlift (HBD) 1RM, 27 resistance-trained men randomly completed 3 sessions that only differed in the activity performed between 2 incremental loading tests that were performed at the beginning (presession) and end (postsession) of the session: (a) control protocol: no training; (b) moderate-fatigue protocol: 5 sets of the HBD exercise at 70% 1RM performing half the maximum possible number of repetitions; and (c) high-fatigue protocol: 5 sets of the HBD exercise performed to failure against the 70% 1RM. Significance was set at an alpha level of 0.05. The reduction of 1RM (p < 0.001), v0 (p = 0.014), and Aline (p < 0.001) at postsession was greater for the high-fatigue protocol, followed by the moderate-fatigue protocol, and finally the control protocol. The changes in L0 did not differ between the fatigue protocols (p = 0.372). The percent change in the 1RM at postsession was significantly correlated with the percent change in Aline (r = 0.714) and L0 (r = 0.540), but not with the percent changes in v0 (r = 0.177). These results suggest that the L-V relationship variables offer a highly sensitive and practical solution for fatigue monitoring.

Abstract: D'Emanuele, S, Boccia, G, Zardo, V, Durigon, V, Schena, F, and Tarperi, C. Strength, rate of force development, and force control evaluations to quantify upper-limbs asymmetries agreement in professional male volleyball players. J Strength Cond Res XX(X): 000-000, 2024-Asymmetries are known to vary based on the nature of the sport and differ between individuals and the tests used. We explored interlimb asymmetries in muscle function among 13 national-level male volleyball players (24 ± 3 years; 87 ± 7 kg; 194 ± 7 cm; 19 ± 2 hours training/week), aiming to determine whether these asymmetries are muscle specific and consistent across various metrics. Subjects underwent assessments for elbow extensors and flexors in both limbs, including maximal contractions to assess the maximal voluntary force (MVF), submaximal ballistic contractions measuring Rate of Force Development (RFDpeak), Scaling Factor (RFD-SF), and evaluations of Approximate Entropy (ApEn), Coefficient of Variations, and Detrended Fluctuation Analysis (DFAα) during sustained contractions. Repeated-mixed ANOVA within and between-factors assessed each metric's differences between muscle groups and limbs. Kappa coefficients (K) were calculated to determine the levels of agreement for the direction of asymmetry among muscle groups and different metrics at the individual level. Our findings revealed that asymmetries were muscle specific, with statistical significance observed only in flexors MVF (12%, p = 0.007, d = 0.68). The asymmetry direction agreement between metrics was null for all parameters except for MVF, which resulted in slight (K = 0.022) and fair (K = 0.308) for ApEn. The agreement between RFDpeak vs MVF (K = 0.386) was fair, slight between RFDpeak vs RFD-SF (K = 0.141), and null when comparing RFDpeak with ApEn and DFAα. At the individual level, no consistent performance advantage was found for either limb, despite volleyball's partial asymmetrical nature, emphasizing the importance of creating personalized training based on the muscle/limb of interest and the parameter to be improved (i.e., maximum strength or RFD).

Abstract: Salter, J, Forsdyke, D, Dawson, Z, Rymer, J, Walsh, L, and Mundy, P. Reliability and sensitivity of using isometric strength and sprint speed measures in adolescent female athletes. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to establish the reliability and sensitivity of isometric mid-thigh pull (IMTP) and sprint speed (5 m, 40 m, and maximal sprint speed) in adolescent women, before exploring the stability of this across maturation to provide maturity-specific benchmarks. A total of 147 female athletes (age: 13.8 ± 2.8 years; stature: 157.1 ± 13.1 cm; body mass: 51.2 ± 15.3 kg; percentage of predicated adult height: 94.3 ± 6.6) performed IMTP and sprint trials on 2 occasions, separated by 7-days. Within- and between-session reliability was determined using intraclass correlation coefficient (ICC), coefficient of variation, and Bland-Altman limits of agreement, with sensitivity detected by signal-to-noise ratios for small (SWC0.2) and moderate (SWC0.5) worthwhile change. A between-group analysis of variance and Cohen's d-effect sizes determined differences between biological maturity groups (pre-, mid-, and post-peak height velocity [PHV]). All isometric strength and sprint performance markers demonstrated either "moderate" or "acceptable" within-session reliability, except for time to peak force (PF) and 40 m sprint. Despite metrics all having "high" or above ICC (0.55-0.98), only PF offered a "good" sensitivity when using SWC0.2, with most offering better sensitivity with SWC0.5. Noise was higher between sessions, resulting in "poor" signal-noise ratios, likely associated with the bias favoring retest trials. Reliability and sensitivity findings were consistent across maturational stages, demonstrating either "moderate" or "acceptable" reliability. There were clear differences between maturity groups for all measures, particularly between mid-PHV and post-PHV. Practitioners can be assured that IMTP and sprint performance measures are reliable within this population but require thorough familiarization processes before confidence in interpreting meaningful changes.

Abstract: Martin, BJ, Wright, M, Patel, V, Susmarski, A, Lovalekar, M, Forse, JN, Beckner, ME, Ledford, AK, and Nindl, BC. Physiological, physical, and psychological determinants of success during the naval special warfare screener selection course. J Strength Cond Res XX(X): 000-000, 2024-The Naval Special Warfare (NSW) screener is an arduous, 24-h course conducted at the Naval Academy in Midshipmen aspiring to enter the Navy's Sea, Air, and Land program. The purpose was to assess and characterize the physiological stress imposed during the 24-hour screener and identify physical, physiological, and psychological differences between finishers and nonfinishers. Forty-eight male Midshipmen between the ages of 18 and 26 years (height = 177.5 ± 6.8 cm, mass = 77.0 ± 5.3 kg, percent body fat = 7.54 ± 2.7%) participated. Before 4-6 weeks of the screener, subjects performed a battery of physical measures, questionnaires, and a cold pressor test (CPT). Blood was collected at baseline, post-CPT, and pre- and postscreener to assess the effects of the screener and differences between finishers and nonfinishers. A total of 48 Midshipmen started the screener, 37 finishers and 11 nonfinishers. Logistic regression revealed that 4 measures significantly increased the likelihood of finishing. A higher likelihood of finishing the screener was observed with Midshipmen with greater height (∼5 cm, p = 0.036), higher anaerobic power (∼0.5 W·kg-1, p = 0.036), greater low-back endurance (∼17 s, p = 0.039), and faster swim times (∼1 minute, p = 0.001). Dehydroepiandrosterone (DHEA) and serum cortisol were both lower after the CPT in finishers (p = 0.042 and 0.004, respectively) but were not different in nonfinishers. Dehydroepiandrosterone and the DHEA:salivary cortisol ratio were lower postscreener in finishers vs. nonfinishers (-70% and -133%, p = 0.008 and 0.001, respectively). In conclusion, this study presents novel findings regarding differences between finishers and nonfinishers of the NSW screener and how a 24-h event of particularly intense stressors affects biomarkers in a select group of Naval Academy Midshipmen.

Abstract: Geneau, MC, Carey, DL, Gastin, PB, Robertson, S, and James, LP. Replicability of strength domains in Australian rules football athletes. J Strength Cond Res XX(X): 000-000, 2024-Maximal lower body strength is a multidimensional construct defined as the maximum force application under specific task constraints. It is crucial for many athletic tasks and is frequently assessed in strength and conditioning environments. Recent technological advancements have increased the number of measurement options for lower body strength, making data interpretation and translation challenging. Principal component analyses (PCA) methods have been proposed to inform strength test and metric selection in field sport athletes, but these methods are limited to cross-sectional designs. This study aimed to investigated the replicability of a PCA method for metric reduction and selection at 2 time points. Thirty-three Australian rules football athletes completed 7 lower body extensor strength tests during preseason (T1) and end of season (T2), each resulting in 280 force-time metrics. At each time point, 9 PCA components were required to explain at least 70% of the variance in the data set, and 7 components demonstrated similar metric loadings onto the components. However, the variable selection procedure did not return the exact same set of variables at both time points. These results suggest that while the number and loading of strength domains are consistent in Australian rules football athletes, the variable selection procedure was not fully replicable. Overall, practitioners can use this information to select tests and metrics within the domains and subdomains identified in this study to capture a range of lower body strength information from their athletes.

Abstract: Miras-Moreno, S, García-Ramos, A, Sašek, M, Cvjetičanin, O, Šarabon, N, Kavčič, I, and Smajla, D. Individual acceleration-speed profile variables: comparison and reliability between linear and curvilinear sprints. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to compare linear sprint (LS) and curvilinear sprint (CS) to provide (a) the goodness-of-fit of individual acceleration-speed profile (ASP) and (b) the magnitude and within- and between-session reliability of the ASP variables (A0 [theoretical maximal acceleration], S0 [theoretical maximal velocity], and ASslope [slope of the linear ASP]). Twenty-one sports science students performed 2 identical experimental sessions composed of 3 LS trials and 6 CS trials (3 for each testing side). The individual ASP was modeled considering only the fastest or combining the 3 trials of each sprint type. The individual ASP presented a very high goodness-of-fit for the 3 sprint types, but slightly higher for best (range r2 = 0.98 [0.75-1.00]) compared with combined trials (range r2 = 0.95 [0.84-0.99]). Linear sprints revealed higher S0 (effect size [ES] ≥ -1.88; p < 0.001) and ASslope (ES ≥ -2.80; p < 0.001) but lower A0 (ES ≥ 1.15; p < 0.001) compared with CS. The ASP variables generally showed an acceptable within-session absolute reliability (range coefficient of variation [CV] = 4.5% [2.4-6.9%]) but an overall poor relative reliability for ASslope (range intraclass correlation coefficient = 0.44 [0.24-0.69]). The between-session reliability was greater for the combined trials (range CV = 4.7% [1.9-8.6%]) compared with the best trial (range CV = 6.1% [2.9-8.7%]). This study opens the possibility of using the ASP to monitor CS, preferably by combining multiple trials to increase its between-session reliability.

Abstract: Gundersen, AH, van den Tillaar, R, Falch, HN, Fredriksen, AB, and Larsen, S. A biomechanical comparison between conventional, sumo, and hex-bar deadlifts among resistance trained women. J Strength Cond Res XX(X): 000-000, 2024-The deadlift is a multijoint exercise frequently used to strengthen the lower extremities and spinal erectors. Despite variations, such as the conventional, sumo, and hex-bar deadlifts, little is known about how these techniques affect the concentric phase of maximal deadlifts among strength trained women. Therefore, this study used statistical parametric mapping to compare kinematics, net joint moments (NJMs), and surface electromyography amplitude between these deadlift variations during the last repetition of a 3 repetition maximum (3RM) in strength trained women. Eleven women (body mass: 67.64 ± 7.27 kg, height: 161.91 ± 3.05 cm, age: 23.18 ± 3.46 years) performed 3RM deadlifts in conventional, sumo, and hex-bar deadlifts, lifting 103.18 ± 18.47, 101.54 ± 15.01, and 99.70 ± 15.94 kg, respectively. The main findings showed that deadlifting with conventional and sumo techniques resulted in larger hip NJMs near the lockout. Conversely, deadlifting with the hex-bar technique resulted in greater barbell velocity, knee NJMs, and increased hip and knee flexion angles. Therefore, when training maximal 3RM deadlifts, we suggest that hex-bar deadlifts may be beneficial for targeting knee extensors and enhancing barbell velocity among strength trained women. Conversely, sumo and conventional deadlifts may be more effective for targeting the hip extensors near the lockout during the last repetition of 3RM deadlifts.

Abstract: Sanders, GJ, Skodinski, S, Cabarkapa, DV, Howard, M, Cabarkapa, D, Kollock, RO, and Peacock, CA. Countermovement jumps and acute to chronic workload ratios in low, moderate, and high jump load groups throughout a Division I volleyball season. J Strength Cond Res XX(X): 000-000, 2024-The purpose of the study was to evaluate the effects of low, moderate, and high jump loads on the acute to chronic workload ratio (ACWR) and neuromuscular fatigue throughout a Division I volleyball season. Twelve female volleyball athletes were monitored throughout a competitive season to track daily jump loads and measure neuromuscular fatigue based on twice-weekly countermovement jumps (CMJs) using a dual force plate. Jump loads were categorized into thirds (low, moderate, high-volume) to assess changes in neuromuscular fatigue, and a secondary evaluation examined differences in the ACWR. The results of this study were statistically significant with a p ≤ 0.05. The Wilks Lambda test in the multivariate analysis of variance found there were main effects for low, moderate, and high jump load groups (F = 50.498, p < 0.001), weeks (F = 3.136, p < 0.001), and significant group by week interactions (F = 1.751, p < 0.001) for jump loads and CMJ test results. There was no main effect of week for ACWR (F = 0.634, p = 0.849), and although statistically different, there were minimal changes in the ACWR between groups. There were significant variations in jump loads and CMJ performance between low, moderate, and high jump load groups across a 16-week season, most notably after week 5. In addition, the data highlight the limitations of the ACWR when detecting changes in athlete fatigue throughout the season.

Abstract: Chen, Z, Xiao, F, Mao, Y, Zhang, X, and García-Ramos, A. An efficient and accurate approach for estimating the free-weight back squat 1-repetition maximum based on the 2-point method and optimal minimal velocity threshold. J Strength Cond Res XX(X): 000-000, 2024-This study aimed to compare the accuracy of nine 1-repetition maximum (1RM) estimation methods based on velocity recordings during the free-weight back squat. In a counterbalanced order, 39 resistance-trained male subjects performed 2 sessions against 6 loads (∼40, 50, 60, 70, 80, and 90% of 1RM) and 2 sessions against only 2 loads (∼40 and 90% of 1RM) followed by the actual 1RM attempts. The first session of each procedure was used for obtaining minimal velocity thresholds (MVTs) and the second session was used for 1RM estimation. Predicted 1RMs were calculated by entering 3 MVTs (i.e., actual MVT [i.e., the MVT associated with the actual 1RM], general MVT [i.e., 0.30 m·second-1], and optimal MVT [i.e., the MVT that minimizes the differences between the actual and predicted 1RMs]) into 3 load-velocity relationship (LVR) regression equations (multiple-point [i.e., using data of 6 loads from the multiple-point test], extracted 2-point [i.e., using data of the lightest and heaviest loads from the multiple-point test], and 2-point [i.e., using data of 2 loads from the 2-point test]). Alpha was set at 0.05. The main findings revealed that only the 1RMs predicted by the optimal MVT showed acceptable accuracy (raw errors ≤0.8 kg, absolute errors ≤4.0%) compared with the actual 1RM. The analysis of variance failed to reveal a significant main effect of the "type of LVR model" (p = 0.079). Therefore, we recommend using the 2-point method combined with the optimal MVT to obtain an efficient and accurate 1RM estimation during the free-weight back squat.