Journal of Strength and Conditioning Research最新文献

Abstract: Tremblay, M, Anderson Sirois, S, Verville, W, Auger, M, Abboud, J, and Descarreaux, M. Acute upper-body and lower-body neuromuscular fatigue effect on baseball pitchers' velocity: A pilot study. J Strength Cond Res 38(8): 1447-1452, 2024-The purpose of this pilot study was to explore the acute effect of upper-body and lower-body neuromuscular fatigue protocols on baseball pitchers' velocity. Sixteen baseball pitchers were recruited, and a crossover design was used to meet the study purpose. Pitchers were tested twice, 7 days apart, with their upper-body and lower-body explosiveness, pitching velocity, and muscle soreness perception of their throwing arm (forearm flexors, biceps, anterior deltoid, and upper trapezius muscles) assessed before and after an upper-body and lower-body neuromuscular fatigue protocol. Two-way analysis of variances and paired t tests ( p < 0.05) were used to identify and compare prescores and postscores. Following both fatigue protocols, results revealed a significant decrease in time for pitching velocity ( p = 0.005, ηp 2 = 0.462), and increases in muscle soreness perception of the forearm flexors ( p = 0.005, ηp 2 = 0.470), anterior deltoid ( p = 0.045, ηp 2 = 0.274), and upper trapezius ( p = 0.023, ηp 2 = 0.339) muscles. Paired t test results showed a significant decrease in preneuromuscular and postneuromuscular fatigue protocol in the upper-body ( p < 0.01) and lower-body ( p < 0.01) explosiveness scores. These pilot study results show the impact of different exercise protocols on pitchers' explosiveness, velocity, and muscle soreness perception emphasizing the need for further investigation into the acute effect of exercise targeting the upper or lower-body on pitching performance, specifically at the pitcher's position.

Abstract: Dawson, L, Beato, M, Devereux, G, and McErlain-Naylor, SA. A review of the validity and reliability of accelerometer-based metrics from upper back-mounted GNSS player tracking systems for athlete training load monitoring. J Strength Cond Res 38(8): e459-e474, 2024-Athlete load monitoring using upper back-mounted global navigation satellite system (GNSS) player tracking is common within many team sports. However, accelerometer-based load monitoring may provide information that cannot be achieved with GNSS alone. This review focuses on the accelerometer-based metrics quantifying the accumulation of accelerations as an estimation of athlete training load, appraising the validity and reliability of accelerometer use in upper back-mounted GNSS player tracking systems, the accelerometer-based metrics, and their potential for application within athlete monitoring. Reliability of GNSS-housed accelerometers and accelerometer-based metrics are dependent on the equipment model, signal processing methods, and the activity being monitored. Furthermore, GNSS unit placement on the upper back may be suboptimal for accelerometer-based estimation of mechanical load. Because there are currently no feasible gold standard comparisons for field-based whole-body biomechanical load, the validity of accelerometer-based load metrics has largely been considered in relation to other measures of training load and exercise intensity. In terms of convergent validity, accelerometer-based metrics (e.g., PlayerLoad, Dynamic Stress Load, Body Load) have correlated, albeit with varying magnitudes and certainty, with measures of internal physiological load, exercise intensity, total distance, collisions and impacts, fatigue, and injury risk and incidence. Currently, comparisons of these metrics should not be made between athletes because of mass or technique differences or between manufacturers because of processing variations. Notable areas for further study include the associations between accelerometer-based metrics and other parts of biomechanical load-adaptation pathways of interest, such as internal biomechanical loads or methods of manipulating these metrics through effective training design.

Abstract: Yeargin, SW, Meyer, CM, Hirschhorn, RM, Lane, AD, Arent, SM, and Haggard, CR. Characterization of health and safety resources for athletes with sickle cell trait at NCAA institutions. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to report the prevalence of student-athletes with sickle cell trait (SCT), determine which screening practices are most commonly used, describe the health and human performance services provided to athletes, and ascertain if differences between National Collegiate Athletic Association (NCAA) designations or divisions exist. A cross-sectional survey design was used to query healthcare administrators regarding SCT resources at their institution. The independent variables were designation (historically Black colleges or universities [HBCUs] or non-HBCU) and Division (DI, DII, and DIII). The dependent variables were SCT prevalence, and the health and human performance services provided to athletes. Of the 60 respondents, HBCU ( n = 16) reported 4.9 ± 2.7% of athletes with SCT, which was higher than non-HBCU (1.1 ± 0.8%; p = 0.022). Historically Black colleges or university reported a higher percentage of student-athletes supplying their own screening results than non-HBCU (52.5 ± 39.2 vs. 12.9 ± 24.0%; p = 0.022). Division III reported higher proportions of waivers than DI (68.3 ± 38.4 vs. 16.9 ± 31.0%; p = 0.010). Most schools ( n = 42, 70.0%) reported having policy and procedures regarding exertional sickling, but none ( n = 60, 100.0%) involved strength and conditioning coaches (SCCs) during development. Practically, a greater proportion of DII and DIII institutions do not have supplemental oxygen available compared with DI but not statistically ( p = 0.058). Pragmatically, the prevalence should be considered when ordering and preparing resources annually. NCAA institutions need to create policy and procedure sections beyond screening. Athletic trainers and SCCs need to have a strong collaborative relationship to optimize health and human performance services.

Abstract: Campbell, P, Maupin, D, Lockie, RG, Dawes, JJ, Simas, V, Canetti, E, Schram, B, and Orr, R. The development of normative fitness data and analyzing the relationships between 20MSFT and 2.4-km run performance in Australian police recruits. J Strength Cond Res XX(X): 000-000, 2024-Aerobic fitness testing plays a significant role in the academy training of law enforcement recruits. There is a lack of normative data for law enforcement recruits and substantial interchangeability for choice of field-based aerobic tests. Therefore, this study aimed to develop normative percentile rankings for the 20-m multistage fitness tests (20MSFT) and 2.4-km run specific to law enforcement recruits; and to analyze the relationship between the 2 tests by linear regression. Data from 5 cohorts of law enforcement recruits completing 20MSFT (n = 1,536) and 2.4-km run (n = 1,499) testing during basic training at an Australian Police Academy were retrospectively analyzed. Percentile ranks were calculated (20th, 40th, 50th, 60th, 80th, and 99th) based on the number of shuttles completed and time (seconds) to complete the 2.4-km run. Results were split by sex and age (i.e., <20 years, 20-29 years, 30-39 years, and 40-49 years). Linear regression analyzed the relationship between the 20MSFT to the 2.4-km run (using both seconds and km·h-1), producing predictive equations to translate scores between the 2 assessments. These data presented the first detailed normative values by age and sex for Australian law enforcement recruits. Furthermore, the results demonstrated regression models could explain 65-74% of the variance observed (r2 = 0.649-0.741) between 20MSFT performance and 2.4-km run performance. This study's findings allow for normative performance for the purpose of benchmarking fitness, setting performance goal, and rehabilitation from injury. In addition, a valid conversion through a linear regression affords cross-agency comparisons and temporal changes in test selection/recruit cohorts.

Abstract: Desai, I, Wewege, MA, Jones, MD, Clifford, BK, Pandit, A, Kaakoush, NO, Simar, D, and Hagstrom, AD. The effect of creatine supplementation on resistance training-based changes to body composition: A systematic review and meta-analysis. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this review was to determine the added effect of creatine supplementation on changes in body composition with resistance training in adults younger than 50 years. The review protocol was preregistered on the Open Science Framework (osf.io/x48a6/). Our primary outcome was lean body mass (LBM); secondary outcomes were body fat percentage (%) and body fat mass (kg). We performed a random-effects meta-analysis in R using the metafor package. Subgroup analyses were conducted to examine the effects of training status and use of a carbohydrate drink with creatine. We conducted a meta-regression to examine the moderating effect of total training volume. Statistical significance was set at p < 0.05. One thousand six hundred ninety-four records were screened, and 67 full-text articles were assessed for eligibility. Twelve studies were included in the meta-analysis. Fifty-two percentages of the studies had low risk, 41% some concerns, and 7% high risk of bias. Compared with resistance training (RT) alone, creatine supplementation increased LBM by 1.14 kg (95% CI 0.69 to 1.59), and reduced body fat percentage by -0.88% (95% CI -1.66 to -0.11) and body fat mass by -0.73 kg (95% CI -1.34 to -0.11). There were no differences between training status or carbohydrate subgroups. Training volume was not associated with effect size in all outcomes; 7 g or 0.3 g/kg of body mass of creatine per day is likely to increase LBM by 1 kg and reduce fat mass by 0.7 kg more than RT alone. Concurrent carbohydrate ingestion did not enhance the hypertrophy benefits of creatine.

Abstract: Bouguezzi, R, Negra, Y, Sammoud, S, Uthoff, A, Moran, J, Behrens, M, and Chaabene, H. The effects of volume-matched 1- and 2-day repeated backward sprint training formats on physical performance in youth male soccer players. J Strength Cond Res XX(X): 000-000, 2024-This study examined the effects of a 6-week, 1 vs. 2 sessions of volume-matched weekly repeated backward sprint training (RBST) on measures of physical fitness in youth male soccer players. Thirty male youth soccer players from a regional soccer team were randomly assigned to a 2-day group (n = 15; age = 16.40 ± 0.64 years; Maturity-offset = 2.19 ± 0.65 years) or a 1-day group (n = 15; age = 16.27 ± 0.51 years; Maturity-offset = 1.91 ± 0.40 years). Measures of jumping ability, linear sprint speed, change-of-direction (CoD) speed, aerobic endurance (AE), and repeated sprint ability (RSA) were measured before and after 6 weeks of training. The training interventions involved 1 to 2 sets, each comprising 7 repetitions over a 20-m distance of RBST in the 2-day group, and 2 to 4 sets, also with 7 repetitions each over the same distance, in the 1-day group. Statistical analyses were conducted using the analysis of covariance model with baseline measurements entered as covariates. Results indicated that RBST over 2 days generated greater benefits compared with a single day for improving CoD speed (∆4.91 vs. 0.04%; effect size [d] = 0.78 vs. 0.00, respectively), linear sprint speed (10-m: ∆4.74 vs. 0.36%; d = 0.96 vs. 0.00, respectively; 20 m: ∆3.34 vs. 0.82%; d = 1.00 vs. 0.49, respectively), and RSA performances (RSAbest: ∆2.61 vs. 0.29%; d = 0.71 vs. 0.16, respectively; RSAmean: ∆2.86 vs. 0.89%; d = 0.59 vs. 0.16, respectively; RSAtotal: ∆2.86 vs. 0.89%; d = 0.62 vs. 0.41, respectively). However, similar improvements in the 2 RBST formats were observed on jumping (2-day group: ∆6.9%; d = 0.75; 1-day group: ∆10.6%, d = 1.26) and AE performance (2-day group: ∆17.24%, d = 1.04; 1-day group: ∆27.25%, d = 2.25). In summary, the findings suggest that, when volume is matched, spreading the RBST regimen over 2 days may result in greater improvements compared with a single-day approach for enhancing CoD speed, linear sprint speed, and RSA performance.

Abstract: Rabal-Pelay, J, Gutiérrez, H, Bascuas, P-J, Pareja-Blanco, F, and Marco-Contreras, LA. Load-velocity relationship in the Bulgarian split-squat exercise. J Strength Cond Res XX(X): 000-000, 2024-The objective of the current research was to analyze the load-velocity relationship in the Bulgarian split-squat (BSS) exercise and to compare these relationships between the dominant and nondominant legs. Twenty-one strength-trained men (age: 27.3 ± 7.3 years) performed a progressive loading test in the BSS exercise using a Smith machine for each leg. The protocol began with a load of 30 kg, incrementally adding 10 kg until the mean propulsive velocity (MPV) fell below 0.4 m·s-1. At that point, 5 kg increments were employed, with a final addition of 2.5 kg for the last estimated attempt one-repetition maximum (1RM). A total of 324 lifts were analyzed. Subjects exhibited a relative strength ratio of 1.23 ± 0.10, a 1RM of 91.3 ± 14.2 kg, and a mean range of motion of 44.7 ± 3.7 cm. Polynomial regression analysis showed a robust relationship with an R2 value of 0.945 (ρ ≤ 0.001) between the relative load (%1RM) and MPV. Despite the differences in 1RM between the dominant and nondominant legs, there were no significant differences in MPV at the %1RM between both legs. These findings suggest that training intensity can be prescribed via the MPV during the BSS exercise. Moreover, the load-velocity relationship is stable between limbs despite the potential differences in absolute strength levels.

Abstract: Leonhardt, TPM, Chilibeck, PD, Ko, J, and Zello, GA. Nutrition knowledge and dietary adequacy in powerlifters. J Strength Cond Res XX(X): 000-000, 2024-Athletes competing in weight categories (e.g., powerlifters) often restrict food intake approaching competition, which may be detrimental to health and performance. Our purpose was to assess the effect of nutrition knowledge, sex, and time (off-season versus precompetition, when athletes often cut weight) on dietary adequacy in powerlifters. Twenty-three powerlifters (10 females; 30.7 ± 11.2 years) completed questionnaires to assess nutrition knowledge and dietary adequacy. Athletes with higher nutrition knowledge consumed more fruits and nuts and less vitamin B2, B3 across all time points (p < 0.05) and a greater number (73%) were above the recommended dietary allowance for vitamin D compared with athletes with lower nutrition knowledge (50%) (p < 0.05). Male powerlifters with higher nutrition knowledge consumed less alcohol and vitamin A than male powerlifters with lower nutrition knowledge (p < 0.05). Female powerlifters with higher nutrition knowledge consumed less sugar and beverage calories than female powerlifters with lower nutrition knowledge (p < 0.05). Intake of alcohol and carbohydrate decreased, and meat calories increased from off-season to precompetition (p < 0.05). Male powerlifters increased B-vitamins, whereas female powerlifters decreased B-vitamin and sugar consumption approaching competition (p < 0.05). Male powerlifters increased water consumption versus female powerlifters approaching competition (sex × time, p < 0.05). There was no effect of nutrition knowledge on dietary changes approaching competition. Nutrition knowledge, sex, and competitive season affect dietary intake of powerlifters. A higher nutrition knowledge predicts a higher intake of some foods and nutrients important for health and performance. Female powerlifters should pay close attention to the intake of B-vitamins and water before competitions when many are trying to cut weight.

Abstract: Calaway, CC, Martinez, KJ, Calzada Bichili, AR, Caplan, JH, Milgrim, WP, Mann, JB, Haq, I, and Signorile, JF. Velocity-based training affects function, strength, and power in persons with Parkinson's disease. J Strength Cond Res XX(X): 000-000, 2024-Velocity-based training (VBT) is commonly associated with high-level athletes. No study has examined the effects of VBT on performance in persons with Parkinson's disease (PD). The objective of the study was to compare the effects of 10 and 30% velocity-loss threshold protocols on changes in functional performance, strength, and power in persons with PD after 12 weeks of supervised VBT, 3 days per week. Twenty-one subjects with PD (72.9 ± 5.9 y) were randomly assigned to the 10% or 30% velocity-loss threshold group and performed the 6-m walk test at habitual and maximal gait speed (6MWTMax), the 5 time sit-to-stand test (5 × STS), 1 repetition maximum (1RM), and peak power (PP) testing for the chest press (CP) and leg press (LP) exercise. A mixed ANOVA with significance was set a priori at 0.05 revealed that significant time effects were seen for the 6MWT at maximal speed (MDiff ± SD = 0.22 ± 0.04 m·s-1, p < 0.001), 5-time sit-to-stand time (-1.48 ± 0.45 seconds, p = 0.005) and power (75.5 ± 22.7 W, p = 0.005), 1RM for CP (5.1 ± 1.1 kg, p < 0.001) and LP (12.6 ± 3.7 kg, p = 0.005), and LP-PP (43.6 ± 13.2 W, p = 0.006). Secondary analyses revealed time effects for the load at which PP was achieved for the CP exercise. A Wilcoxon signed-rank test revealed no significant differences in the percentage of 1RM at which PP was achieved for either condition. Results indicate that VBT is an effective training modality for improving functional capacity, strength, and power in persons with PD; however, shifts in force-velocity relationships were not evidenced.

Abstract: Skratek, J, Kadlubowski, B, and Keiner, M. The effect of traditional strength training on sprint and jump performance in 12- to 15-year-old elite soccer players: a 12-month controlled trial. J Strength Cond Res XX(X): 000-000, 2024-The aim of the study was to evaluate the effect of traditional strength training on maximum strength (1 repetition maximum in front squat [FS] and back squat [BS]), jump (squat and countermovement jump), and linear sprint (LS) performance (5, 10, and 30 m) in elite young soccer players. A 12-month longitudinal design was chosen, and 48 elite male youth soccer players (age: 12-15 years) were included. The subjects were divided in 2 groups (a strength training group [STG] and a control group [CG]). The intervention group trained for 1 year over a competitive soccer season with additional sessions to their regular soccer practice (4 sessions per week), while the CG did not complete any additional sessions to the regular soccer training (4 sessions per week). The additional strength training (2 sessions per week [each approximately 30 minutes]) consisted of either parallel FS or BS. The squat variants switched in each session. Data were analyzed using a 2 × 3 (group × time) repeated-measures analysis of variance. The main findings of this study were that the STG resulted in significant pretest and post-test improvements in maximum strength (d = 3.75-5.58), jump (d = 0.84-1.14), and LS performance (d = -0.25 to 0.44), while for the CG, smaller increases or performance decreases were measured (maximum strength: d = 1.64-2.7; jump: d = 0.12-0.31; sprint: d = 0.00-025). A significant interaction effect in all variables indicated significant (p < 0.05) stronger performance improvements compared with the CG. Traditional strength training in elite youth soccer players is recommended to increase strength and speed-strength (jump and sprint performance) and should be considered in long-term athletic development programs.