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In recent years, the EnodePro® device has been one of the most frequently used velocity sensors to track the bar velocity in resistance training, with the aim of providing load–velocity profiles. However, recent articles highlight a lack of reliability and validity in the estimated maximal strength, which can cause a serious health risk due to the overestimation of the bar velocity. With this study, we aimed to investigate whether imprecision in the measurement could explain the variance in this measurement error. Methods: The research question was evaluated by comparing the integrated velocities from the EnodePro® with the velocities from a high-resolution displacement sensor for the squat and bench press. The velocity was measured with loads corresponding to 30%, 50%, and 70% of the one-repetition maximum (1RM) in moderately trained participants (n = 53, f = 16, m = 37). Intraclass correlation coefficients (ICC) for agreement were supplemented by an exploration of the systematic bias and the random error (mean absolute error (MAE), mean absolute percentage error (MAPE)). Results: The results indicated movement specificity, with the ICC values for the squat ranging from 0.204 to 0.991 and with ICC = 0.678–0.991 for the bench press. Systematically higher velocities were reported by the EnodePro® sensor (p < 0.001–0.176), with an MAE = 0.036–0.198 m/s, which corresponds to an MAPE of 4.09–42.15%. Discussion: The EnodePro® seems to provide overly high velocities, which could result in the previously reported overestimation of the 1RM. Despite the validity problems of force/load–velocity profiles, we suggest evaluating the bar velocity with accurate measurement devices, which is, contrary to previous reports, not the case with the EnodePro®. [ABSTRACT FROM AUTHOR]

Introduction: While maximum strength diagnostics are applied in several sports and rehabilitative settings, dynamic strength capacity has been determined via the one-repetition maximum (1RM) testing for decades. Because the literature concerned several limitations, such as injury risk and limited practical applicability in large populations (e.g., athletic training groups), the strength prediction via the velocity profile has received increasing attention recently. Referring to relative reliability coefficients and inappropriate interpretation of agreement statistics, several previous recommendations neglected systematic and random measurement bias. Methods: This article explored the random measurement error arising from repeated testing (repeatability) and the agreement between two common sensors (vMaxPro and TENDO) within one repetition, using minimal velocity thresholds as well as the velocity = 0 m/s method. Furthermore, agreement analyses were applied to the estimated and measured 1RM in 25 young elite male soccer athletes. Results: The results reported repeatability values with an intraclass correlation coefficient (ICC) = 0.66-0.80, which was accompanied by mean absolute (percentage) errors (MAE and MAPE) of up to 0.04-0.22 m/s and =7.5%. Agreement between the two sensors within one repetition showed a systematic lower velocity for the vMaxPro device than the Tendo, with ICCs ranging from 0.28 to 0.88, which were accompanied by an MAE/MAPE of =0.13 m/s (11%). Almost all estimations systematically over/underestimated the measured 1RM, with a random scattering between 4.12% and 71.6%, depending on the velocity threshold used. Discussion: In agreement with most actual reviews, the presented results call for caution when using velocity profiles to estimate strength. Further approaches must be explored to minimize especially the random scattering. [ABSTRACT FROM AUTHOR]

Speed strength performances are heavily dependent on maximum strength. However, various strength testing methods determined inconsistent relationships between absolute and relative strength and sprint and jump performances. The aim of the study was to calculate the one tailed correlation coefficients between both the One-Repetition Maximum (1RM) and 1RM in relation to body mass (1RM/BM) in parallel squats and different jump (squat jump and countermovement jump) and sprint performances (5-, 10-, 20-, and 30-m) in youth soccer players (n= 63, 17.9±2.1 years old). Relative strength showed significantly larger correlations with jump performances (r= 0.52 to 0.58) than absolute strength (r= 0.16 to 0.26, z= -1.81 to -1.90, p= 0.029 to 0.035). However, the r values between relative strength measures and sprint performances (r= -0.32 to -0.42) were of non-statistical difference to the correlations of absolute strength measurements with sprint performances (r= -0.19 to -0.3, z= 0.349 to 1.17, p= 0.121 to 0.363). The results of this study support findings in previous literature of enhanced speed strength performances by higher levels of maximal strength in youth soccer players, with faster and more powerful athletes being able to generate larger forces against their own body weight. The data suggests that strength expressed relative to body mass might be considered as a superior predictor of speed strength performance in general. [ABSTRACT FROM AUTHOR]

Introduction While all running athletes aim to cover the prescribed distance as fast as possible, the physiological and anatomical profiles of athletes are completely different between the disciplines. While sprint athletes have to exert maximal force in the smallest possible time window, the long-distance runner strives for the most economical movement pattern possible (Barnes & Kilding, 2015). Therefore, defined as oxygen uptake at a velocity at a prescribed percentage of the vVO2max, running economy (RE) has been identified as a decisive performance parameter (Saunders et al., 2004). One identified parameter which moderates RE was Achilles tendon stiffness. While stretching frequently used in warm-ups, it also decreases tissue stiffness. Objective: While some authors recommended the avoidance of stretching prior to running (Wilson et al., 2010), others found no affected economy in response to stretching. To address this research gap, this study was conducted to pool available stretching effects on RE. Methods A systematic search was conducted using MEDLINE/PubMed, Web of Science and Scopus (inception to April, 2024), which was supplemented by a manual search in Google Scholar and reference lists of identified studies. To account for multiple dependent study outcomes, robust variance estimation meta-analysis model was chosen to quantify pooled effect sizes. Controlled acute and chronic studies were included if they were performed in young, healthy participants on RE-parameter (energy/O2-consumption at a prescribed velocities determined at a percentage of VO2max (vVO2). Studies without a control group, patients or without the metabolic parameters were excluded. The PEDro scale and GRADE criteria were applied to evaluate the risk of bias and certainty of evidence, respectively. Results A total of 16 studies were investigated, with 14 studies (6 static stretching, 6 dynamic stretching and 2 static/dynamic stretching) addressing acute effects with 169 participants and 33 effect sizes (ES) matched the inclusion criteria. With a PEDro score of 4.88, study quality was rated fair. Overall, there was a low certainty of evidence without confirming any effect of stretching on RE, with overall group effect of ES = 0.007, -0.15 to 0.17 [95% CI], p = .93, τ2 = 0, W2 = 0, static group effect of ES = -0,22, -0,40 to 0,70 [95% CI], p = .3, τ2 = 0.18, W2 = 0 and dynamic group effect of ES = -0,07, -0.22 to 0.09 [95% CI], p = .35, τ2 = 0, W2 = 0, determined at vVO2 65% - 90%. Discussion Currently, there is no evidence supporting previous recommendations to avoid stretching before running due to reduced RE. However, several methodological limitations, such as high heterogeneity in the velocity used in RE determination, small study sample sizes and comparatively short stretching durations without intensity quantification and a lack of pre-post comparisons bias the certainty of evidence. Accordingly, there is a demand for high quality research that controls underlying mechanisms. [ABSTRACT FROM AUTHOR]

The American College of Sports Medicine classifies flexibility as one out of 5 important health-related parameters that should be addressed in preventive and therapeutic training programs (Garber et al., 2011). Due to its importance in health and athletic performance development, there is an increasing number of studies to figure out flexibility training interventions as well as underlying mechanisms. While several exercise modalities are available, stretching and foam rolling (FR) are the most common training routines to improve range of motion (ROM). Interestingly, acute and chronic effects are mainly attributed to very similar mechanisms, more specifically, improved stretch tolerance and/or structural adaptations such as stiffness reductions in the muscle, the tendon, or the muscle-tendon complex (Takeuchi et al., 2023). Since stretching and FR seem to induce similar effect sizes in acute flexibility, authors suggested the replacement of static stretching to FR in movement preparation routines to avoid the stretch-induced force deficit, thus, impairments of subsequent strength related performance. Similarly, when discussing chronic flexibility routine effects, literature suggests task specificity. Therefore, increased ROM was attributed to specific stretch/foam rolling induced stiffness and passive peak torque changes. Unfortunately, statements developed from used research designs are incomprehensive. When referring to acute stretching of foam rolling effects that can be extracted from numerous systematic reviews, conclusions were drawn from comparisons to passive controls. This, however, does exclusively allow statements that stretching/FR was effective compared to doing nothing, however, does not exclude general warm-up effects, induced by muscle activity. Referring to William of Ockham (1287 - 1347), one popular philosopher from the United Kingdom, the most obvious explanatory approach would be the most likely one. In medicine diagnostics, this statement is metaphorically described as "when hearing hoof beats from behind, expect horses, not zebras". Therefore, since both routines enhance temperature, the most likely explanation suggest acute ROM increases could rely on general warm-up effects instead of task-specific adaptations. Similarly, for chronic effects, literature suggests that ROM can be increased by several alternative interventions, e.g. full ROM resistance training, indicating shared mechanisms. Both interventions share underlying physiological mechanisms, such as inducing mechanical tension in high muscle lengths. Consequently, we extensively discussed available evidence in our published research. Key findings will be presented to challenge current paradigms (Warneke et al., 2024). [ABSTRACT FROM AUTHOR]

Objectives : Increasing exercise intensity and performance output with superimposed vibration gains interest, especially in high-performance training. However, the additional benefit of vibration in passive stretching exercises and its mechanisms remain unclarified. Methods : Passive stretching with (ST+V) and without (ST) vibration (20 Hz) was performed in male Olympic youth skiing athletes ( n = 8, age: 17.9 ± 1.0 years) using a single-blinded randomized cross-over design. Acute hip abduction, hip anteversion, knee extension, and hamstrings (stand and reach straight leg raise) range of motion (ROM) were assessed using a digital goniometer, while stiffness was examined via MyotonPRO. The skin temperature of the whole leg was captured with infrared thermography and analyzed in different segments. Results : Both stretching interventions increased ROM compared to the control group (CG) ( p < 0.001-0.033, d = 1.0-1.6) without differences between ST+V and ST ( p = 0.202-0.999). While skin temperature decreased in the CG and ST, ST+V maintained a constant temperature in the lower legs. Stiffness was not affected by both stretching interventions. Conclusions : The stretching intervention leads to significant increases in flexibility, while additional vibration did not further enhance the ROM.

To improve flexibility, stretching is most commonly used and in training interventions duration-dependent effects are hypothesized. However, there are strong limitations in used stretching protocols in most studies, particularly regarding documentation of intensity and performed procedure. Thus, aim of this study was to compare different stretching durations on flexibility in the plantar flexors and to exclude potential biases. Eighty subjects were divided into four groups performing daily stretching training of 10min (IG10), 30min (IG30) and 1h (IG60) and one control group (CG). Flexibility was measured in bended and extended knee joint. Stretching was performed with a calf muscle stretching orthosis to ensure long-lasting stretching training. Data were analysed with a two-way ANOVA for repeated measures on two variables. Two-way ANOVA showed significant effects for time (η 2 = 0.557-0.72, p < 0.001) and significant interaction effects for time × group (η 2 = 0.39-0.47, p < 0.001). Flexibility in the knee to wall stretch improved with 9.89-14.46% d = 0.97-1.49 and 6.07-16.39% with d = 0.38-1.27 when measured via the goniometer of the orthosis. All stretching times led to significant increases in flexibility in both tests. While there were no significant differences measured via the knee to wall stretch between the groups, the range of motion measurement via the goniometer of the orthosis showed significantly higher improvements in flexibility depending on stretching duration with the highest increase in both tests with 60 minutes of stretch per day.