ECSS Paris 2023: OP-AP28
INTRODUCTION: Flywheel resistance training is commonly used to enhance muscle strength, power, and the performance of athletic tasks. Where the extent of eccentric overload (EO) provided by traditional flywheel systems is variable and often difficult to induce, recently developed motorised flywheel systems may provide a more consistent stimulus. Therefore, this study aimed to quantify how inertial load and motorised versus non-motorised modes influence concentric and eccentric mechanical outputs in flywheel squats. METHODS: Twelve resistance-trained males (age 26.5 ± 5.40 years; one-repetition maximum back squat 1.70 ± 0.29 kg/body-mass) completed multiple sets of half-squats on a flywheel device under motorised (20% eccentric boost) and non-motorised modes across six inertial loads (0.025–0.15 kg·m²), following a randomised, within-subject, counterbalanced crossover design. Mean and peak power were recorded during concentric and eccentric phases using a linear position transducer and a strain gauge. For each variable, the eccentric-concentric ratio was calculated to characterise EO. Data were analysed using linear mixed-effects models, with differences between flywheel modes, across phases and inertias, quantified via comparisons of estimated marginal means (in raw units) supplemented with standardised effect sizes (Hedges’ g calculated with raw data). RESULTS: Compared to the non-motorised mode, the motorised mode produced significantly higher eccentric mean and peak power across all inertial loads (p < 0.001, mean power = 279 to 713 W vs 199 to 525 W; peak power = 833 to 2195 W vs 746 to 1552 W), except for peak power at lower inertial load (0.025 kg·m², p > 0.05), with differences between modes tending to increase in tandem to inertia in both mean and peak power (g = 0.29 to 2.40). The non-motorised mode elicited significantly greater concentric mean and peak power at higher inertial load ranges than the motorised mode (0.10-0.15 kg·m², p < 0.01, g= 0.55 to 0.90, mean power= 355 to 632 W vs 394 to 568 W; peak power = 925 to 1569 W vs 969 to 1340 W). Notably, while concentric power peaked within the measured range, eccentric power in the motorised mode tended to increase continuously across the range of inertias. Regarding EO, motorised mode elicited stepwise increases in ratios for both mean and peak power (p < 0.001, mean power EO ratio = 0.79-1.46; peak power EO ratio = 0.98-1.85), whereas the non-motorised mode showed significant increases in eccentric-concentric ratios only for mean power (p < 0.05, EO ratio = 0.65-0.89). CONCLUSION: Motorised flywheel systems provide a superior eccentric stimulus compared to traditional non-motorised flywheels, substantially increasing EO across a range of inertial loads. These findings have important implications for eccentric-focused training prescription, although the translation of these acute mechanical advantages into long-term performance adaptations requires further investigation.
Read CV Dogus BakiciECSS Paris 2023: OP-AP28
INTRODUCTION: Unaccustomed high-intensity eccentric contractions typically induce exercise-induced muscle damage (EIMD) in sedentary individuals. The Repeated Bout Effect (RBE) describes a protective adaptation where a prior bout attenuates damage from a subsequent bout. While ipsilateral and homologous contralateral RBE (cross-education) are well-documented, evidence regarding heterologous contralateral RBE (e.g., lower limb training protecting upper limb) remains limited. This study aimed to investigate whether an initial maximal eccentric exercise (MaxEc) in the lower limbs could reduce muscle fatigue and enhance performance in the contralateral upper limbs during a subsequent bout two weeks later. METHODS: Twenty-four sedentary females (18–30 years) were randomized into an experimental group (KE-CEF, n=12) and a control group (CEF, n=12). The KE-CEF group performed MaxEc on non-dominant knee extensors (60 reps), followed 14 days later by MaxEc on non-dominant elbow flexors (30 reps), while the CEF group performed only the elbow flexor MaxEc. Dependent variables including Maximal Voluntary Isometric Contraction (MVC) and muscle stiffness via Acoustic Radiation Force Impulse (ARFI) were assessed at baseline, immediately post-exercise (D0), and daily for 5 days (D1-D5). RESULTS: The KE-CEF group demonstrated significantly superior recovery compared to the CEF group across multiple indices. For muscle strength, the KE-CEF group exhibited greater MVC at D0 (20.26 ± 5.84 N·m/kg) compared to the CEF group (16.26 ± 4.11 N·m/kg, p = 0.029). Regarding concentric strength, the KE-CEF group maintained stability with no significant decline from baseline (26.05 ± 5.38 N·m/kg) across all time points (p > 0.05), whereas the CEF group significantly decreased at D0 (11.05 ± 4.45 N·m/kg) compared to baseline (18.29 ± 4.88 N·m/kg, p < 0.0001). In terms of muscle stiffness (ARFI), the CEF group showed a significant increase at D1 (1.14 ± 0.06 m/s) compared to baseline (0.96 ± 0.03 m/s, p = 0.001), while the KE-CEF group stabilized quickly after D0. CONCLUSION: This study confirms a "heterologous contralateral repeated bout effect," where lower limb training protects the upper limb. This aligns with recent findings that eccentric conditioning of knee extensors enhances elbow flexor recovery, suggesting systemic adaptations beyond local tissues [1]. The preserved strength supports the concept of skeletal muscle "cellular memory" and cross-adaptation, where initial stress activates broad protective pathways benefiting remote muscles [2]. Furthermore, the superior functional stability observed is consistent with evidence that contralateral protection is driven by central neural adaptations rather than peripheral changes, optimizing motor unit recruitment [3]. Clinically, these findings advocate for heterologous contralateral training as a viable strategy to preserve neuromuscular function in immobilized or injured upper limbs.
Read CV Fu-Shun HsuECSS Paris 2023: OP-AP28
INTRODUCTION: During a strength training workout, the exercise order can influence performance, training-induced fatigue and subsequent adaptations. To date, most of the research on exercise sequencing has primarily investigated exercises that target the same muscle group. However, real-life resistance training workouts typically involve exercises for multiple muscle groups performed in the same training session and with different sequences, limiting the practical applicability of existing evidence. Therefore, the purpose of the present study was to investigate the acute effects of high-intensity resistance exercise sequencing for upper- and lower-body muscle groups on the performance of the second exercise in the sequence. METHODS: Eighteen moderately trained young adults (20.0 ± 2.2 years; 74.4 ± 10.1 kg; 172.2 ± 9.7 cm) were randomly assigned to two groups with a crossover design. In the first week, one group performed upper-body (bench press; BP) exercise followed by lower-body (leg press; LP) exercise (BP→LP), while the other group performed the reverse sequence (LP→BP). In the second week, the exercise order was reversed for both groups. Exercise intensity was set at the 6-repetition maximum (6-RM) for each exercise. Force and velocity were recorded for each repetition during all sets of BP and LP. Moreover, mean power output and velocity were calculated. RESULTS: No significant differences were observed in mean power output or movement velocity for the second exercise performed in the sequence, regardless of exercise order (p > 0.05, η2 = 0.032 – 0.172). CONCLUSION: These findings suggest that performing one upper-body and lower-body resistance exercise in a training workout, the sequence of exercises does not negatively affect acute performance or training quality. This indicates that when only one exercise per muscle group is performed within a training workout (i.e. due to limited time availability) individuals may be flexible regarding exercise order for a more practical training setting.
Read CV Thomas MpampoulisECSS Paris 2023: OP-AP28