The Duration of Non-Local Muscle Fatigue Effects.

Non-local muscle fatigue (NLMF) refers to a transient decline in the functioning of a non-exercised muscle following the fatigue of a different muscle group. Most studies examining NLMF conducted post-tests immediately after the fatiguing protocols, leaving the duration of these effects uncertain. The aim of this study was to investigate the duration of NLMF (1-, 3-, and 5-minutes). In this randomized crossover study, 17 recreationally trained participants (four females) were tested for the acute effects of unilateral knee extensor (KE) muscle fatigue on the contralateral homologous muscle strength, and activation. Each of the four sessions included testing at either 1-, 3-, or 5-minutes post-test, as well as a control condition for non-dominant KE peak force, instantaneous strength (force produced within the first 100-ms), and vastus lateralis and biceps femoris electromyography (EMG). The dominant KE fatigue intervention protocol involved two sets of 100-seconds maximal voluntary isometric contractions (MVIC) separated by 1-minute of rest. Non-dominant KE MVIC forces showed moderate and small magnitude reductions at 1-min (p < 0.0001, d = 0.72) and 3-min (p = 0.005, d = 0.30) post-test respectively. The KE MVIC instantaneous strength revealed large magnitude, significant reductions between 1-min (p = 0.021, d = 1.33), and 3-min (p = 0.041, d = 1.13) compared with the control. In addition, EMG data revealed large magnitude increases with the 1-minute versus control condition (p = 0.03, d = 1.10). In summary, impairments of the non-exercised leg were apparent up to 3-minutes post-exercise with no significant deficits at 5-minutes. Recovery duration plays a crucial role in the manifestation of NLMF.

The Effects of Physical and Mental Fatigue on Time Perception.

The perception of time holds a foundational significance regarding how we elucidate the chronological progression of events. While some studies have examined exercise effects on time perception during exercise periods, there are no studies investigating the effects of exercise fatigue on time perception after an exercise intervention. This study investigated the effects of physical and mental fatigue on time estimates over 30 s immediately post-exercise and 6 min post-test. Seventeen volunteers were subjected to three conditions: physical fatigue, mental fatigue, and control. All participants completed a familiarization session and were subjected to three 30 min experimental conditions (control, physical fatigue (cycling at 65% peak power output), and mental fatigue (Stroop task)) on separate days. Time perception, heart rate, and body temperature were recorded pre-test; at the start of the test; 5, 10, 20, 30 seconds into the interventions; post-test; and at the 6 min follow-up. Rating of perceived exertion (RPE) was recorded four times during the intervention. Physical fatigue resulted in a significant (p = 0.001) underestimation of time compared to mental fatigue and control conditions at the post-test and follow-up, with no significant differences between mental fatigue and control conditions. Heart rate, body temperature, and RPE were significantly (all p = 0.001) higher with physical fatigue compared to mental fatigue and control conditions during the intervention and post-test. This study demonstrated that cycling-induced fatigue led to time underestimation compared to mental fatigue and control conditions. It is crucial to consider that physical fatigue has the potential to lengthen an individual's perception of time estimates in sports or work environments.

Chronic effects of stretching on range of motion with consideration of potential moderating variables: A systematic review with meta-analysis.

BACKGROUND: It is well known that stretch training can induce prolonged increases in joint range of motion (ROM). However, to date more information is needed regarding which training variables might have greater influence on improvements in flexibility. Thus, the purpose of this meta-analysis was to investigate the effects of stretch training on ROM in healthy participants by considering potential moderating variables, such as stretching technique, intensity, duration, frequency, and muscles stretched, as well as sex-specific, age-specific, and/or trained state-specific adaptations to stretch training. METHODS: We searched through PubMed, Scopus, Web of Science, and SportDiscus to find eligible studies and, finally, assessed the results from 77 studies and 186 effect sizes by applying a random-effect meta-analysis. Moreover, by applying a mixed-effect model, we performed the respective subgroup analyses. To find potential relationships between stretch duration or age and effect sizes, we performed a meta-regression. RESULTS: We found a significant overall effect, indicating that stretch training can increase ROM with a moderate effect compared to the controls (effect size = -1.002; Z = -12.074; 95% confidence interval: -1.165 to -0.840; p < 0.001; I2 = 74.97). Subgroup analysis showed a significant difference between the stretching techniques (p = 0.01) indicating that proprioceptive neuromuscular facilitation and static stretching produced greater ROM than did ballistic/dynamic stretching. Moreover, there was a significant effect between the sexes (p = 0.04), indicating that females showed higher gains in ROM compared to males. However, further moderating analysis showed no significant relation or difference. CONCLUSION: When the goal is to maximize ROM in the long term, proprioceptive neuromuscular facilitation or static stretching, rather than ballistic/dynamic stretching, should be applied. Something to consider in future research as well as sports practice is that neither volume, intensity, nor frequency of stretching were found to play a significant role in ROM yields.

Corticospinal excitability and reflex modulation in a contralateral non-stretched muscle following unilateral stretching.

PURPOSE: Muscle stretching effect on the range of motion (ROM) and force deficit in non-stretched muscle, and the underlying mechanisms, is an ongoing issue. This study aimed to investigate crossover stretching effects and mechanisms on the plantar flexor muscles. METHODS: Fourteen recreationally active females (n = 5) and males (n = 9) performed six sets of 45-s static stretching (SS) (15-s recovery) to the point of discomfort of the dominant leg (DL) plantar flexors or control (345-s rest). Participants were tested for a single 5-s pre- and post-test maximal voluntary isometric contraction (MVIC) with each plantar flexor muscle and were tested for DL and non-DL ROM. They were tested pre- and post-test (immediate, 10-s, 30-s) for the Hoffman (H)-reflex and motor-evoked potentials (MEP) from transcranial magnetic stimulation in the contralateral, non-stretched muscle. RESULTS: Both the DL and non-DL-MVIC force had large magnitude, significant (↓10.87%, p = 0.027, pƞ2 = 0.4) and non-significant (↓9.53%, p = 0.15, pƞ2 = 0.19) decreases respectively with SS. The SS also significantly improved the DL (6.5%, p < 0.001) and non-DL (5.35%, p = 0.002) ROM. The non-DL MEP/MMax and HMax/MMax ratio did not change significantly. CONCLUSION: Prolonged static stretching improved the stretched muscle's ROM. However, the stretched limb's force was negatively affected following the stretching protocol. The ROM improvement and large magnitude force impairment (statistically non-significant) were transferred to the contralateral muscles. The lack of significant changes in spinal and corticospinal excitability confirms that the afferent excitability of the spinal motoneurons and corticospinal excitability may not play a substantial role in non-local muscle's ROM or force output responses.

Resistance Training Induces Improvements in Range of Motion: A Systematic Review and Meta-Analysis.

BACKGROUND: Although it is known that resistance training can be as effective as stretch training to increase joint range of motion, to date no comprehensive meta-analysis has investigated the effects of resistance training on range of motion with all its potential affecting variables. OBJECTIVE: The objective of this systematic review with meta-analysis was to evaluate the effect of chronic resistance training on range of motion compared either to a control condition or stretch training or to a combination of resistance training and stretch training to stretch training, while assessing moderating variables. DESIGN: For the main analysis, a random-effect meta-analysis was used and for the subgroup analysis a mixed-effect model was implemented. Whilst subgroup analyses included sex and participants' activity levels, meta-regression included age, frequency, and duration of resistance training. DATA SOURCES: Following the systematic search in four databases (PubMed, Scopus, SPORTDiscus, and Web of Science) and reference lists, 55 studies were found to be eligible. ELIGIBILITY CRITERIA: Controlled or randomized controlled trials that separately compared the training effects of resistance training exercises with either a control group, stretching group, or combined stretch and resistance training group on range of motion in healthy participants. RESULTS: Resistance training increased range of motion (effect size [ES] = 0.73; p < 0.001) with the exception of no significant range of motion improvement with resistance training using only body mass. There were no significant differences between resistance training versus stretch training (ES = 0.08; p = 0.79) or between resistance training and stretch training versus stretch training alone (ES = - 0.001; p = 0.99). Although "trained or active people" increased range of motion (ES = 0.43; p < 0.001) "untrained and sedentary" individuals had significantly (p = 0.005) higher magnitude range of motion changes (ES = 1.042; p < 0.001). There were no detected differences between sex and contraction type. Meta-regression showed no effect of age, training duration, or frequency. CONCLUSIONS: As resistance training with external loads can improve range of motion, stretching prior to or after resistance training may not be necessary to enhance flexibility.