ECSS Paris 2023: OP-AP02
INTRODUCTION: Sprint performance is related to the muscle size and strength of lower-limb muscles such as the hip flexors and knee extensors. However, little is known about how training-induced changes in muscle size and strength of these muscle groups contribute to sprint performance enhancement. Thus, this study compared the effects of hip flexion (HF) versus knee extension (KE) training on muscle size, muscle strength and sprint performance. We also examined whether training-induced changes in sprint performance were associated with changes in muscle size and strength. METHODS: Forty-five healthy untrained adults completed 12 weeks of either HF (n = 23) or KE (n = 22) training. Participants trained each leg unilaterally at 70% of one-repetition maximum (1RM) for 5 sets of 10 repetitions per session, twice weekly. Before and after the intervention, HF 1RM (HF-1RM), KE 1RM (KE-1RM), MRI-derived volumes of 13 individual muscles (including hip flexors, knee extensors and adductors) and 60-m sprint time were assessed. Training effects were evaluated using linear mixed models. Repeated-measures correlations examined associations between changes in sprint time and changes in muscle volumes and each 1RM, and stepwise multiple regression analyses were conducted, separately for each group. RESULTS: Increases in hip flexor volume were significantly greater following HF training (+12.7%) than KE training (+6.9%), whereas increases in knee extensor volume were greater following KE training (+4.1%) than HF training (+1.0%) (P ≤ 0.004). Similarly, HF-1RM increased more after HF training (+112.3%) than KE training (+18.9%), and KE-1RM increased more after KE training (+46.5%) than HF training (+24.5%) (P < 0.001). Sprint time showed a significant main effect of time (P = 0.005) with no group by time interaction (P = 0.515), indicating similar reductions in sprint time in both groups (HF: −1.5% vs. KE: −0.9%). Within-group analyses revealed that in the HF group, changes in sprint time were significantly correlated with changes in HF-1RM, KE-1RM, hip flexor volumes, knee extensor volumes and hip adductor volumes (r = −0.462 to −0.654, P ≤ 0.023). Among these correlated variables, rectus femoris hypertrophy emerged as a significant predictor for sprint time improvement in stepwise regression (R2 = 0.222, P = 0.001). In contrast, no significant associations were observed in the KE group, although changes in rectus femoris (r = −0.518) and tensor fasciae latae (r = −0.557) volumes showed trends toward associations with changes in sprint time (both P = 0.074). CONCLUSION: Both HF and KE training induced different task-specific increases in muscle size and strength, whilst similarly improving sprint performance. However, associations between muscle adaptations and sprint performance enhancement were evident primarily in the HF group, suggesting that training-induced changes in muscles contributing to HF may be particularly relevant for sprint performance enhancement.
Read CV Naoya NishizawaECSS Paris 2023: OP-AP02
INTRODUCTION: Block periodization sequences training phases to potentiate adaptations from strength endurance to maximal strength and power (1, 2, 3). Although widely applied in high-performance sport, empirical evidence describing the time course of neuromuscular, sprint mechanics, and morphological adaptations in track and field athletes remains limited. This study examined phase-specific adaptations across a block-periodized off-season in NCAA Division I sprinters and jumpers. METHODS: Eighteen NCAA Division I sprinters and jumpers completed an 11-week long intervention consisting of sequential Strength-Endurance (SE, 4 weeks), Basic Strength (BS, 4 weeks), and Strength-Power (SP, 3 weeks) blocks. Testing was performed at Baseline, post-SE, post-BS, and post-SP. Neuromuscular performance was assessed using squat jumps (SJ) and countermovement jumps (CMJ) on dual force plates (1000 Hz). Sprint performance was evaluated over 30 m with 10 m splits, and sprint mechanical variables were derived from macroscopic force-velocity profiling (4). Vastus lateralis cross-sectional area (CSA) was assessed using B-mode ultrasonography. Adaptations were analyzed using linear mixed-effects models. RESULTS: Morphological adaptations were phase-specific, with CSA increasing significantly after SE (F = 3.021, p = 0.042) and remaining elevated through SP. Jump performance followed a potentiated pattern: SJ height increased significantly only after SP (F = 5.233, p = 0.003), whereas CMJ height improved after SE and SP (F = 18.100, p < 0.001). Kinetically, SJ peak force increased during SE and BS (F = 35.970, p < 0.001), while SJ peak power improved after BS (F = 24.397, p < 0.001). In the CMJ, peak propulsive power increased significantly after BS (F = 4.884, p = 0.005), while peak force decreased following SE (F = 12.89, p < 0.001). Sprint performance improvements were confined to early acceleration, with faster 0-10 m times observed after BS (F = 5.745, p < 0.001) and maintained through SP, with no changes in later splits. These changes were driven by increases in force-related mechanical variables rather than velocity. However, the ratio of horizontal-to-resultant force decreased across the later blocks (F = 7.159, p < 0.001), indicating reduced horizontal force application efficiency despite greater force production capability. CONCLUSION: Block-periodized off-season training elicited phase-specific adaptations consistent with the phase potentiation model. SE training induced hypertrophy, BS enhanced force production and early acceleration, and SP training facilitated the expression of explosive performance. Acceleration improvements were primarily mediated by enhanced force capacity rather than velocity, while horizontal force application efficiency declined across the off-season. [1] Stone 2021/ [2] DeWeese 2015/ [3] Suchomel 2018 / [4] Morin 2016
Read CV Jose Francisco Barquero JimenezECSS Paris 2023: OP-AP02
INTRODUCTION: Low-load blood-flow restriction (BFR) training induces muscle hypertrophy comparable to high-load (HL) resistance training, but strength gains are typically smaller as neural adaptations appear attenuated. Yet, effects of BFR compared to HL on muscle contractile properties remain unknown. Therefore, we investigated how BFR affects muscle contractile properties and whether a sequential combination of BFR with subsequent short-term HL increases neural adaptations. METHODS: After familiarization, 37 healthy adults completed a randomized controlled trial comparing BFR (11 males: 47.3±6.0 years, 12 females: 49.7±7.2 years) and HL (5 males: 45.0±6.1years; 10 females: 47.3±5.9 years) knee extensor training over 8 weeks, followed by 2-weeks HL in both groups. Maximal voluntary contraction (MVC) was quantified during isometric knee extension using dynamometry (ScienceToPractice LtD, Ljubljana, Slovenia). Rate of torque development (RTD) was calculated within 250ms of force onset in 50ms windows. Voluntary activation (VA) of the knee extensor muscles was determined using the interpolated twitch technique. Vastus lateralis (VL) and Rectus femoris (RF) volume was calculated based on 5 anatomical cross-sections at 30-70% of thigh length spaced 10% apart using ultrasound (12L3, Acuson Juniper, Siemens, Erlangen, Germany). VL muscle thickness, fascicle length (FL) and pennation angle (PA) was assessed at rest at 50% of thigh length and 50% muscle width using ultrasound (LF9, ArtUS, Telemend, Milano, Italy). Maximum fascicle shortening velocity was determined within first 250ms of force onset. RESULTS: Linear mixed models were used to analyze group*time interactions and Cohen's d effect sizes are reported. After both training phases, the BFR group showed smaller improvements than HL in VA (d = −0.31 to −0.37) and knee extension MVC (d = −0.16 to −0.27). RF and VL volume increases did not favor of any group (d = −0.01 to 0.08). RTD did not change relevantly between groups. VL thickness, PA, and FL showed negligible differences between groups (d = −0.04 to 0.16) at rest. Maximum fascicle shortening velocity decreased more pronounced in the HL group (d = −0.66). CONCLUSION: While both training paradigms did not differ in muscle volume changes, a subsequent 2-week HL phase in the BFR group did not fully restore neural adaptations to the level of continuous HL training. Importantly, although more than 1200 architectural images were analyzed to assess reliability of manual and automated analysis, the magnitude of observed architectural changes remained within the range of measurement variability. Thus, ultrasound-based architectural measures appear insufficiently sensitive to detect intervention effects of the magnitude typically observed in resistance training studies. These findings underscore the central role of mechanical loading for neural adaptation and highlight the necessity of explicitly reporting and interpreting reliability metrics in longitudinal ultrasound research.
Read CV Paul RitscheECSS Paris 2023: OP-AP02