Journal of Strength and Conditioning Research最新文献

Abstract: Haynes, H, Tinsley, GM, Swafford, SH, Compton, AT, Moore, J, Donahue, PT, and Graybeal, AJ. Mobile anthropometry in Division I baseball athletes: evaluation of an existing application and the development of new equations. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to evaluate the agreement between mobile application and dual-energy x-ray absorptiometry (DXA)-derived body composition parameters in a group of Division I (DI) collegiate baseball athletes and to develop new equations for this population using this mobile technique. A total of 41 (age: 20.5 ± 1.5 years; DXA %fat: 18.9 ± 4.6%) DI collegiate baseball athletes underwent body composition assessments using DXA and a mobile anthropometric application. Total and appendicular body composition estimates were produced from this mobile application using previously developed equations and evaluated against the reference (DXA) in the complete sample of athletes. Least absolute shrinkage and selection operator regressions were then used to develop new equations using the mobile application in a portion of the athletes (n = 34) and subsequently tested in the remaining athletes (n = 7). In the complete sample, no body composition estimate using the mobile application's existing equations (R2: 0.00-0.68) demonstrated equivalence with DXA, including estimates of %fat (R2: 0.37; root-mean-squared error [RMSE]: 3.74%), fat mass (FM), and total (appendicular lean mass [ALM]) and leg lean mass ([ALMlegs] R2: 0.67-0.68; RMSE: 3.43-4.86 kg). In the testing sample, estimates produced from the newly developed equations demonstrated acceptable performance when compared to DXA, most notably %fat (R2: 0.80; RMSE: 3.66%), FM, ALM, and ALMlegs (R2: 0.55-0.87; RMSE: 0.74-3.46 kg). Previously developed equations using mobile anthropometrics may not demonstrate acceptable agreement with DXA in DI collegiate baseball athletes, and newly developed equations specific to this group may be more suitable. Those employing these newly developed equations should use caution until further external cross-validation is performed.

Abstract: Rivera-Köfler, T, Varela-Sanz, A, Padrón-Cabo, A, Giráldez-García, MA, and Muñoz-Pérez, I. Effects of polarized training vs. other training intensity distribution models on physiological variables and endurance performance in different-level endurance athletes: a scoping review. J Strength Cond Res XX(X): 000-000, 2024-This scoping review aimed to analyze the long-term effects of polarized training (POL) on key endurance physiological- and performance-related variables and to systematically compare them with other training intensity distribution (TID) models in endurance athletes of different performance levels. Four TID models were analyzed: POL, pyramidal (PYR), threshold (THR), and block (BT) training models. The literature search was performed using PubMed, SportDiscus, Scopus, and Web of Science databases. Studies were selected if they met the following criteria: compared POL with any other TID model, included healthy endurance athletes, men, and/or women; reported enough information regarding the volume distribution in the different training intensity zones (i.e., zone 1, zone 2, and zone 3), assessed physiological (i.e., maximum/peak oxygen uptake, speed or power at aerobic and anaerobic thresholds, economy of movement), and performance in competition or time-trial variables. Of the 620 studies identified, 15 met the eligibility criteria and were included in this review. According to scientific evidence, POL and PYR models reported greater maximum oxygen uptake enhancements. Both POL and PYR models improved the speed or power associated with the aerobic threshold. By contrast, all TID models effectively improved the speed or power associated with the anaerobic threshold. Further research is needed to establish the effects of TID models on the economy of movement. All TID models were effective in enhancing competitive endurance performance, but testing protocols were quite heterogeneous. The POL and PYR models seem to be more effective in elite and world-class athletes, whereas there were no differences between TID models in lower-level athletes.

Abstract: Oddsson, HR, Friðgeirsdóttir, KÝ, Hafliðadóttir, L, Einarsson, IÞ, Kristjánsdóttir, H, and Saavedra, JM. Differences in anthropometric parameters, physical fitness, and kicking speed in young football players according to performance level, playing position, and relative age effect: a population-based study. J Strength Cond Res XX(X): 000-000, 2024-The objectives of this study were to determine (a) the differences, both in male and female players, in anthropometric parameters, physical fitness, and kicking speed based on the players' level and position on the field; (b) whether there is a relative age effect based on the players' level, and (c) whether there is a relationship between the relative age effect and the anthropometric parameters, physical fitness, and kicking speed parameters. Eight hundred twenty-six football players (15.76 ± 2.60 year old, 75.7% male) participated in the study. Players were grouped into elite and nonelite, as well as based on their field position and birth quartile. Nonparametric tests were used to study differences by level and by position or trimesters. Chi-square goodness of fit analysis was performed to know the association between elite and nonelite players regarding the relative age effect. Physical fitness parameters and kicking speed were higher in elite players than in nonelite players (5.834 ≥χ2 ≤ 48.079; p < 0.001). There were differences in anthropometric and physical fitness parameters and kicking speed depending on the player's position: goalkeeper vs. outfield players (7.648 ≥χ2 ≤ 26.078; p < 0.001) except in jump tests. There was a relative age effect in elite male players (χ2 = 26.313; p < 0.001) but not in female players, and it was related to anthropometric and physical fitness parameters. This population-based study offers insights into the variables that differentiate elite from nonelite players at young ages, with differences in the relative age effect between male and female players, which can be used by coaches to identify key performance variables.

Abstract: He, P, Ye, Z, Liu, M, Zhang, Y, Zhou, C, Zhang, Y, Yang, S, and Qin, X. Associations of handgrip strength, walking pace, and genetic risks with incident arrhythmias. J Strength Cond Res XX(X): 000-000, 2024-We quantified the associations of handgrip strength and walking pace with incident arrhythmias using Cox proportional hazards models with hazards ratios (HRs). The study included 487,673 subjects, with an average age of 56.4 years, 54.8% female, and free of baseline arrhythmias from the UK Biobank prospective study. Handgrip strength was assessed by a dynamometer. Low handgrip strength was defined as less than 27 kg in men and 16 kg in women. Walking pace was self-reported as slow, average, or brisk. The arrhythmia categories involved incident atrial fibrillation (AF), incident ventricular arrhythmias, and incident bradyarrhythmia, respectively. Over a median follow-up duration of 12.4 years, 28,967 (5.9%), 4,061 (0.8%), and 11,741 (2.4%) subjects developed incident AF, incident ventricular arrhythmias, and incident bradyarrhythmia, respectively. Compared with those with low handgrip strength, the adjusted HRs (95% confidence interval [CI]) of incident AF, ventricular arrhythmias, and bradyarrhythmia in subjects with normal handgrip strength were 0.76 (95% CI: 0.73.-0.79), 0.75 (95% CI: 0.67.-0.84), and 0.80 (95% CI: 0.74.-0.85), respectively. Compared with those with a slow walking pace, subjects with a brisk walking pace had significantly lower risks of incident AF (HR, 0.56; 95% CI: 0.53.-0.58), ventricular arrhythmias (HR, 0.52; 95% CI: 0.45.-0.59), and bradyarrhythmia (HR, 0.63; 95% CI: 0.59.-0.68). In addition, the inverse associations of handgrip strength and walking pace with AF were significantly stronger among those with a lower genetic risk of AF (both p interaction <0.001). In conclusion, handgrip strength and walking pace were inversely associated with incident arrhythmias. The inverse associations for incident AF were stronger in those with a lower genetic risk of AF.

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: 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: 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: 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.