Background and Objectives: The Nordic hamstring exercise (NHE) effectively strengthens the hamstrings, reduces the risk of hamstring strain, and induces fatigue in the muscles; thus, post-NHE recovery strategies should be optimized. Foam rolling (FR) is a widely used method, with the belief that it can speed up recovery. Thus, this study investigated the acute and 48-h effects of FR following the NHE on muscle stiffness, pain pressure threshold (PPT), flexibility, countermovement jump (CmJ) height, and maximal voluntary isometric contraction (MVIC). Materials and Methods: Thirty-two active males were randomly assigned to either an FR group (n = 16) or a passive recovery (PR, n = 16) group. Measurements were taken at three time points: pre-test, post-test_0h, and post-test_48h. Participants performed the NHE (3 sets × 10 reps) before the recovery interventions. Variables assessed included muscle stiffness (MyotonPro), flexibility (sit and reach), PPT (algometer), jump performance (force platform), and MVIC peak torque (dynamometer). Results: FR significantly improved acute flexibility (12.7%, p < 0.001) following the NHE and prevented flexibility loss at 48 h, compared to the PR group. However, FR showed no significant advantages over PR in terms of muscle stiffness, PPT, CmJ, or MVIC, both acutely and at 48 h (p > 0.05). Conclusions: FR is an effective acute recovery strategy for improving flexibility after the NHE but offers limited effects for muscle stiffness, PPT, and other functional muscle parameters, both acutely and at 48 h. Further research should explore the long-term effects and efficacy of FR across diverse populations and recovery scenarios.

This study examined muscle excitation using surface electromyography (sEMG) during different ranges of motion (ROM) in the bench press. Given the limited research on upper-body muscle excitation across ROMs, this study aimed to establish reference values for muscle excitation in distinct bench press ROMs. Nineteen male participants performed a 10-repetition maximum (10RM) bench press across three ROMs: full ROM, upper-half ROM, and lower-half ROM. sEMG measurements were taken on the pectoralis major (PM), triceps brachii (TB), and anterior deltoid (AD). Mean and peak EMG amplitudes were analyzed. Significant differences in mean muscle excitation were observed across all muscles (p < 0.001–0.002). The upper-half ROM elicited the highest mean excitation for the TB, while both partial ROMs resulted in greater excitation for the PM and AD compared to the full ROM. Peak muscle excitation was significantly greater in the PM sternocostal 15% region during the upper-half ROM. Additionally, the TB long and lateral heads showed significantly higher peak EMG values in the upper-half ROM than in the other conditions. These results suggest that ROM variations in the bench press lead to distinct muscle excitation patterns. This insight may inform future research on ROM’s effects on muscle hypertrophy and strength development.

Purpose: A single session of complex contrast training (CCT) can induce lower-limb fatigue, making the optimization of post-CCT recovery strategies essential. Foam rolling (FR) is widely used and is believed to enhance acute recovery. Therefore, this study examined the acute effects of FR compared with passive recovery (PR) following a single bout of CCT on dynamic balance (YBT), static balance (SLST), horizontal jump performance (SLHD), vertical jump performance (CMJ), and muscle excitation measured via surface electromyography (sEMG). Methods: Twenty-one active males completed the study using a crossover design, being randomly allocated to FR and PR conditions. Assessments were performed at three time points: pre-test, immediately post-CCT (mid-test), and after the recovery intervention (post-test). Participants performed the CCT protocol prior to recovery (5 sets × 6 repetitions at 80% and 30% of 1RM). Test measures included YBT, SLST, SLHD, CMJ, and sEMG recordings from selected lower-limb muscles. Results: FR resulted in significant acute improvements in YBT, SLST, and SLHD compared with PR (p < 0.05), whereas no meaningful differences were detected in CMJ performance (p > 0.05). Although time effects were observed in sEMG excitation for some muscles (p < 0.05), no intervention × time interactions were detected (p > 0.05). Conclusions: FR is an effective acute recovery strategy for enhancing dynamic and static balance as well as horizontal jump performance following CCT. However, its influence on vertical jump performance and muscle excitation appears limited. Future research should incorporate broader neuromuscular assessments, varied FR protocols, and diverse populations to better clarify underlying mechanisms and optimize recovery outcomes.

A single session of explosive resistance exercise can induce acute neuromuscular fatigue, highlighting the need for effective recovery strategies. Foam rolling (FR) is commonly used to facilitate neuromuscular and functional restoration. This study examined whether FR, compared with passive recovery (PR), differentially affects post-exercise balance, jump performance, and lower-limb neuromuscular excitation assessed via surface electromyography. Twenty-one physically active men (age 21.8 ± 1.6 years; height 180.7 ± 8.0 cm; weight 75.1 ± 10.8 kg) completed both FR and PR in a randomized crossover design. Assessments were conducted prior to exercise (pre-test), immediately post-exercise (mid-test), and following the recovery interventions (post-test). All participants performed the squat jump protocol (5 sets × 6 reps at 30% 1RM and 6–8 reps at body weight), followed by performance tests (dynamic balance, static balance, horizontal and vertical jumping) and muscle activity assessment. For physical tests, significant intervention × time interactions were observed for posteromedial and composite scores of dynamic balance, static balance, and horizontal jumping (p = 0.002–0.024; \({\upeta}_{\text{p}}^{2}\) = 0.171–0.262), indicating greater improvements following FR compared with PR, whereas no significant interactions were observed for anterior and posterolateral dynamic balance or vertical jumping. Muscle excitation showed significant main effects of time across all measures (p ≤ 0.001–0.032; \({\upeta}_{\text{p}}^{2}\) = 0.158–0.598), with intervention × time interactions limited to a subset of muscles (p = 0.011–0.035; \({\upeta}_{\text{p}}^{2}\)= 0.154–0.201). FR may help preserve static and dynamic balance, as well as horizontal jump performance, following a single bout of explosive resistance exercise; however, its effects on vertical jump and muscle excitation appear limited. Future research should incorporate broader neuromuscular assessments and varied FR protocols across diverse populations to clarify underlying mechanisms and optimize recovery.

Resistance training is crucial for athletic performance and clinical rehabilitation (El-Kotob et al., 2020). Practitioners frequently use acute surface electromyography (sEMG) to select exercise variations (AdavamPurath et al., 2020), assuming greater acute muscle excitation equates to superior long-term adaptations. However, sEMG amplitude does not directly reflect neural drive, and this paradigm lacks robust empirical validation (Vigotsky et al., 2022). Furthermore, stretch-mediated hypertrophy evidence suggests that training in lengthened partial ranges of motion (ROM) drives growth via passive mechanical tension, with almost no active sEMG excitation (Warneke et al., 2023). This PhD project therefore tests whether acute sEMG amplitude predicts 12-week changes in regional muscle hypertrophy and strength, regardless of whether the relationship proves strong or absent. Secondarily, the study contrasts full ROM (FROM) with lengthened partial ROM (LROM) to test the predictive utility of sEMG across mechanical stimuli (Plotkin et al., 2023). Methods: The project implements a three-stage framework: Phase 1: Evidence Synthesis (Completed): A scoping review mapped how training intensity, ROM, and repetition duration influence acute sEMG amplitude. Phase 2: Acute Biomechanical Investigations (Completed): Two laboratory studies (10RM bench press and prone barbell row) quantified neuromuscular responses across full, upper-half, and lower-half ROM conditions. Phase 3: Longitudinal Trial: A 12-week unilateral, intra-individual intervention in untrained adults (target n = 20, a priori sample size estimation based on Pallarés et al., 2021). In bi-weekly leg extension and leg curl sessions (8-10RM), the right leg trains with FROM (2s/2s), while the left leg trains with LROM (fully stretched position, 1s/1s). Regional muscle thickness (ultrasound) and MVIC torque will be correlated with standardized baseline 10RM sEMG recordings normalized to MVIC. Results: Phases 1 and 2 have been published, demonstrating that exercise execution parameters modulate acute sEMG amplitude significantly and muscle-specifically. The Phase 3 trial is currently underway with high participant compliance (>95%). Post-intervention data collection will conclude in August 2026. Conclusion: This project directly tests a widely applied but under-validated assumption. If predictive validity is confirmed, sEMG will be justified as a resource-efficient tool for evaluating training protocols. Conversely, if the relationship proves weak, or if LROM yields differential adaptations independent of baseline sEMG, this will caution against relying on acute sEMG and underscore passive mechanical tension as a driver of hypertrophy. Either way, and accounting for the likely muscle-specificity of the relationship, this work advances evidence-based exercise prescription from athletic performance to sarcopenia counter-measures. References AdavamPurath, F., et al. (2020). Activity of shoulder girdle muscles during the perfect push-up and push-up bar exercises using different hand positions in young overhead athletes. Sport Sciences for Health. El-Kotob, R., et al. (2020). Resistance training and health in adults: An overview of systematic reviews. Applied Physiology, Nutrition, and Metabolism. Pallarés, J. G., et al. (2021). Effects of range of motion on resistance training adaptations: A systematic review and meta-analysis. Scandinavian Journal of Medicine and Science in Sports. Plotkin, D. L., et al. (2023). Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift. Frontiers in Physiology. Vigotsky, A. D., et al. (2022). Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy. Sports Medicine. Warneke, K., et al. (2023). Physiology of Stretch-Mediated Hypertrophy and Strength Increases: A Narrative Review. Sports Medicine.

Introduction & PurposeRunning economy (RE), defined as oxygen consumption at a given submaximal running speed, is a key determinant of endurance performance and can vary substantially even among athletes with similar maximal oxygen uptake (VO2MAX)(Saunders et al., 2004). Research has shown that muscle–tendon unit (MTU) properties, particularly muscle and tendon stiffness, influence RE (Arampatzis et al., 2006). Specifically, lower stiffness of the quadriceps MTU and greater stiffness of the triceps surae MTU have been associated with enhanced RE (Arampatzis et al., 2006). Such differences may be explained by the distinct biomechanical functions of these muscle groups during running. Musculoskeletal analyses of running mechanics have demonstrated that the quadriceps muscle primarily contributes to braking and support during the initial stance phase, whereas the plantar flexors primarily contribute to propulsion and support during the subsequent late stance phase (Hamner et al., 2010). Therefore, it can be hypothesized that different mechanical properties may be advantageous for different MTUs, with a more compliant quadriceps tendon potentially facilitating energy absorption during braking and a stiffer triceps surae MTU potentially enhancing elastic energy recoil during propulsion. As resistance training and stretching interventions can modify MTU properties (Albracht & Arampatzis, 2013; Konrad et al., 2015), they may affect RE by altering the mechanical characteristics of the locomotor system. In line with these mechanisms, resistance training has repeatedly been shown to have beneficial effects on RE (Llanos-Lagos et al., 2024), whereas evidence for the effects of stretching interventions remains limited, especially regarding chronic adaptations (Warneke et al., 2025). Therefore, interventions specifically targeting individual MTUs may represent a more suitable approach than non-specific lower-limb interventions. It has been demonstrated that proprioceptive neuromuscular facilitation (PNF) stretching has the potential to reduce tendon stiffness (Konrad et al., 2015), whereas prolonged high-volume stretching interventions may additionally decrease muscle stiffness (Nakamura et al., 2021). Moreover, isometric strength training has been associated with increased Achilles tendon stiffness and improvements in RE (Albracht & Arampatzis, 2013). Therefore, specifically reducing quadriceps MTU stiffness through PNF stretching while increasing triceps surae MTU stiffness through isometric resistance training may represent a promising, though exploratory, approach to potentially optimize RE. To date, the impact of an isolated quadriceps PNF stretching intervention or its combination with isometric plantar flexor training on RE has not been researched. The purpose of this study is to investigate the isolated and combined effects of chronic PNF stretching of the quadriceps MTU and isometric strength training of the triceps surae MTU on RE in recreational runners. MethodsIn this ongoing randomized controlled trial, recreational runners were recruited and subsequently allocated to one of four groups (resistance training, stretching, combined intervention, or control) using a computer-generated simple randomization. An a priori power analysis indicated a minimum required sample size of 56 participants (f = 0.4, α = 0.05, power = 0.80). The intervention period lasted 14 weeks, with all interventions performed three times per week in addition to participants' habitual endurance training. The stretching intervention consisted of high-volume PNF stretching using a contract–relax protocol targeting the quadriceps. Each set consisted of alternating 12 seconds of passive stretching and 8 seconds of maximal quadriceps contractions, which were repeated three times per leg prior to switching sides. This procedure was repeated for 10 sets per leg. The resistance intervention consisted of high-intensity isometric plantar flexion training, targeting the triceps surae. Participants were instructed to perform seated isometric calf raises with extended knees at 90% of their maximal voluntary isometric contraction intensity. Each training session consisted of five sets per leg, with each set including four repetitions of three-second contractions, separated by three-second rest intervals, and two-minute rest between sets. Training intensity was regularly adjusted throughout the intervention period. The combined group performed both interventions, whereas the control group maintained their habitual training routines without additional intervention. To determine individual running velocities and ventilatory thresholds, all runners completed an incremental exercise test (IET) on the treadmill. After a recovery period of at least 48 hours, participants completed a RE assessment consisting of a 15-minute run at 10% below the second ventilatory threshold (VT2), followed by a time-to-exhaustion (TtE) run at 10% above VT2 until volitional exhaustion. The RE was determined from oxygen consumption during the final five minutes of the submaximal running stage. Biomechanical running parameters were assessed simultaneously during this period. To investigate potential underlying mechanisms, MTU structure and function were assessed before and after the intervention period. Ultrasound shear-wave elastography (SWE; Aixplorer, SuperSonic Imagine, Aix-en-Provence, France) was used to assess patellar and Achilles tendon stiffness. A linear SL10-2 transducer with a 500 kPa measurement range was used for the patellar tendon, and an SL15-4 transducer with a 1400 kPa range for the Achilles tendon, both with penetration mode enabled. Probe pressure was minimized throughout all measurements. The transducer position was marked on transparent foil and replicated during post-testing, while probe orientation was standardized using a digital angle-measurement application. For both tendons, the region of interest covered the...