Due to its high relevance in sports and rehabilitation, the exploration of interventions to further optimize flexibility becomes paramount. While stretching might be the most common way to enhance range of motion, these increases could be optimized by imposing an additional activation of the muscle, such as mechanical vibratory stimulation. While several original articles provide promising findings, contradictory results on flexibility and underlying mechanisms (e.g., stiffness), reasonable effect size (ES) pooling remains scarce. With this work we systematically reviewed the available literature to explore the possibility of potentiating flexibility, stiffness, and passive torque adaptations by superimposing mechanical vibration stimulation. A systematic search of 4 databases (Web of Science, MEDLINE, Scopus, and Cochrane Public Library) was conducted until December 2023 to identify studies comparing mechanical vibratory interventions with passive controls or the same intervention without vibration (sham) on range of motion and passive muscle stiffness in acute (immediate effects after single session) and chronic conditions (multiple sessions over a period of time). ES pooling was conducted using robust variance estimation via R to account for multiple study outcomes. Potential moderators of effects were analyzed using meta regression. Overall, 65 studies (acute: 1162 participants, chronic: 788 participants) were included. There was moderate certainty of evidence for acute flexibility (ES = 0.71, p < 0.001) and stiffness (ES = -0.89, p = 0.006) effects of mechanical vibration treatments vs. passive controls without meaningful results against the sham condition (flexibility: ES = 0.20, p < 0.001; stiffness: ES = -0.19, p = 0.076). Similarly, moderate certainty of evidence was found for chronic vibration effects on flexibility (control: ES = 0.64, p = 0.043; sham: ES = 0.65, p < 0.001). Lack of studies and large outcome heterogeneity prevented ES pooling for underlying mechanisms. Vibration improved flexibility in acute and chronic interventions compared to the stand-alone intervention, which can possibly be attributed to an accumulated mechanical stimulus through vibration. However, studies on biological mechanisms are needed to explain flexibility and stiffness effects in response to specific vibration modalities and timing.

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.

Falls are a leading cause of morbidity in older adults, and muscle weakness accompanied by gait impairments is a major contributing risk factor. Although current guidelines refer to resistance training, the literature lacks high-quality moderator analyses to evidentially guide clinicians to best treatment practice. This systematic review with meta-analysis opposed pooled resistance training effects to passive controls or active alternative interventions to distinguish specific resistance training effects from generally enhanced physical activity on gait and falls relevant outcomes. Effect sizes (ES) were pooled using robust variance estimation generally and for potential moderators. Ninety-two (92) studies with 5932 participants (mean age 73.1 ± 4.9 years) revealed large improvements in strength (ES = 0.86, p < 0.001) and moderate magnitude effects on gait outcomes (ES = 0.59, p < 0.001). Largest effects were reached for timed up-and-go (ES = 0.97), followed by gait distance (ES = 0.65), sit-to-stand (ES = 0.42), and gait speed (ES = 0.41) when compared with passive control. Active comparator analyses (stretching, walking, multicomponent exercises) outlined superior effectivity in the timed up-and-go performance (ES = 0.42) only. Supervision, progressive intensity regulation, and inclusion of multi-joint lower-limb exercises (leg press, squat, ankle plantarflexion, knee extension) positively affected results. Spatiotemporal and kinetic gait parameters were not significantly affected in general. Although some positive effects were observed when compared against a passive control, for most outcomes, the analysis questioned current guidelines as the specificity of resistance training effects was blurred by neglectable differences to alternative training interventions. This could be attributed to a dearth of high-quality evidence (long-term studies, reasonable intensity, and volume) on gait parameters in older adults. Graphical Abstract

Purpose: Vibrational stimulation was suggested sufficient to acutely enhance range of motion (ROM). However, the actual merit of superimposed vibration and underlying mechanical or sensory mechanisms of ROM increases due to local vibration are not well understood. Methods: Using a randomized controlled cross-over trial, this study opposed two minutes of stretching + vibration (STV) to vibration (V) and stretching (ST) alone as well as a passive control (CG) in 30 healthy, recreationally active participants. Pre- and post-intervention measurements of ankle dorsiflexion ROM, ankle passive torque, and gastrocnemius medialis muscle stiffness were conducted using a dynamometer and shear wave elastography, respectively. Results: All interventions significantly increased ROM (p < 0.001, η ² = 0.622) compared to CG, with no additional benefits observed for vibration combined with stretching compared to stretching or vibration alone. However, combining stretching and vibration produced the most pronounced reductions in passive torque over the whole ankle ROM. The combination demonstrated additive effects of stretching and vibration, which affected passive torque in the end ROM and at rest, respectively. Muscle stiffness decreased, but did not differentiate between conditions. Conclusion: These findings negate additional acute vibration effects on ROM that surpass the effects of stretching alone, while the combination of stretching and vibration presented the most prominent influence on passive torque and joint resistance. Vibration also increases stretching pain tolerance; this might facilitate the conduction of exercises and improves compliance as well as adherence to stretching habits.

Background: High standardization is of crucial relevance for reliability in imaging diagnostics. When quantifying muscle properties (muscle thickness and stiffness) by ultrasound or myotonometry, internal validity can be compromised by examiner-related factors and participant biologic variability. A frequently neglected source of bias is pre-measurement activity, which may acutely alter muscle perfusion and muscle blood inflow. Methods: The acute influence of different physical activity routines on tissue parameters was investigated in 30 healthy participants (16 m, 14f). Ten minutes before, immediately before, immediately after and 10 min retention of cycling, jogging, calf raises or control, muscle thickness and stiffness measurements via shear wave elastography (SWE) and myotonometry were measured. Results: Reliability was excellent for muscle thickness (ICC = 0.94–1.00; CV = 1.7–9.1%), good-excellent for SWE stiffness (ICC = 0.68–0.97; CV = up to 26% for inter-day) and myotonometry (muscle ICC = 0.77–0.98; CV = 4.0–17% tendon 0.86–0.93 (CV = 11–17%). Muscle thickness significantly increased after calf raises (d = 1.60, 10.3%) and jogging (d = 0.60, 3.0%), without effects after cycling or control. Shear-wave elastography showed muscle stiffness decreased after calf raises (d=-0.73, -16.7%). Myotonometry indicated a stiffness increase (d = 1.04, 20.1%). The 10-minute retention showed consistent effects for muscle thickness (d = 0.80, 5.3%) and stiffness (SWE: d = 0.78, 21.1%, myotonometry: d=-0.82, -13.0%). Conclusion: Pre-measurement activity could systematically affect muscle thickness and stiffness with dependence on activity type and intensity. This highlights the importance of monitoring pre-measurement activity to minimize potential reliability issues as this, depending on several potential moderators, could enhance the random error if within sample pre-measurement activity is not standardized. Before ultrasound evaluation, for some activity (i.e. calf raises), > 10 min of rest was required to diminish this bias.

Purpose: Stretching is a common strategy to acutely improve range of motion (ROM). Underlying mechanisms typically involve stretch tolerance and reduced tissue stiffness. Alternatively, vibration training can be used to improve ROM which can be attributed to circulatory and neural mechanisms. While combining stretching with vibration yields small benefits in young and healthy adults, evidence in older adults is scarce. The objective was to investigate whether superimposing vibration on stretching provides acute ROM benefits compared to stretching alone on flexibility, muscle–tendon stiffness, and skin temperature. Methods: Conducted as assessor-blinded, randomized cross-over study with three conditions, eight participants performed either stretching + vibration (ST + V), stretching alone (ST), and passive control (CG). ROM was evaluated via the passive straight-leg-raise and active sit-and-reach test. Biceps femoris and Achilles tendon stiffness were measured via myotonometry. Skin temperature was captured via infrared thermography. Results: Both intervention conditions improved passive ROM by large effect sizes ( d = 2.16–3.16, p < 0.001), but only ST + V enhanced active ROM ( d = 1.23, p = 0.048). Vibration superimposition also significantly moderated viscoelastic parameters and maintained/elevated calf skin temperature, whereas temperature declined in ST and CG by moderate to high effect size. Achilles tendon stiffness decreased immediately after ST ( d = − 1.24, p = 0.049) and 30 min after ST + V ( d = − 1.64, p = 0.015). Conclusion: Discussing the tonic vibration reflex as underlying mechanism, this study showed superimposed vibration increased active ROM and decreased stiffness. Although additional vibration could offer additional practical benefits for flexibility interventions in aging populations, the clinical relevance must be further investigated in larger populations. Trial Registration : This clinical trial was retrospectively registered at www.drks.de (ID: DRKS00037552, date: 31.07.2025).