Reduced isometric knee extensor force following anodal transcranial direct current stimulation of the ipsilateral motor cortex.

BACKGROUND: The goal of this study was to determine if 10-min of anodal transcranial direct current stimulation (a-tDCS) to the motor cortex (M1) is capable of modulating quadriceps isometric maximal voluntary contraction (MVC) force or fatigue endurance contralateral or ipsilateral to the stimulation site. METHODS: In a randomized, cross-over design, 16 (8 females) individuals underwent two sessions of a-tDCS and two sham tDCS (s-tDCS) sessions targeting the left M1 (all participants were right limb dominant), with testing of either the left (ipsilateral) or right (contralateral) quadriceps. Knee extensor (KE) MVC force was recorded prior to and following the a-tDCS and s-tDCS protocols. Additionally, a repetitive MVC fatiguing protocol (12 MVCs with work-rest ratio of 5:10-s) was completed following each tDCS protocol. RESULTS: There was a significant interaction effect for stimulation condition x leg tested x time [F(1,60) = 7.156, p = 0.010, ηp2 = 0.11], which revealed a significant absolute KE MVC force reduction in the contralateral leg following s-tDCS (p < 0.001, d = 1.2) and in the ipsilateral leg following a-tDCS (p < 0.001, d = 1.09). A significant interaction effect for condition x leg tested [F(1,56) = 8.12, p = 0.006, ηp2 = 0.13], showed a significantly lower ipsilateral quadriceps (to tDCS) relative MVC force with a-tDCS, versus s-tDCS [t(15) = -3.07, p = 0.016, d = -0.77]. There was no significant difference between the relative contralateral quadriceps (to tDCS) MVC force for a-tDCS and s-tDCS. Although there was an overall significant [F(1,56) = 8.36, p < 0.001] 12.1% force decrease between the first and twelfth MVC repetitions, there were no significant main or interaction effects for fatigue index force. CONCLUSION: a-tDCS may be ineffective at increasing maximal force or endurance and instead may be detrimental to quadriceps force production.

Menthol-Based Topical Analgesic Induces Similar Upper and Lower Body Pain Pressure Threshold Values: A Randomized Trial.

CONTEXT: Both health professionals and consumers use menthol-based topical analgesics extensively for the temporary relief of pain from musculoskeletal ailments or injury. However, there are no reports of differences in the pain pressure threshold (PPT) or the relative effectiveness of topical analgesics to reduce pain in the upper and lower body muscles and tendons. The objective of this study was to investigate whether differences existed in PPT and relative pain attenuation associated with a menthol-based topical analgesic over a variety of upper and lower body muscles and tendons. DESIGN: Randomized allocation, controlled, intervention study. METHODS: Sixteen participants (10 females and 6 males) were tested on their dominant or nondominant side. The order of specific muscle/tendon testing was also randomized, which included upper body (middle deltoid, biceps brachii, and lateral epicondylar tendon) and lower body locations (quadriceps, hamstrings, gastrocnemius, lumbosacral erector spinae muscles, and patellar and Achilles tendons). The PPT was monitored before and 15 minutes following the application of a menthol-based topical analgesic. RESULTS: A menthol-based topical analgesic increased PPT (decreased pain sensitivity) overall (P = .05; 11.6% [2.4%]; d = 1.05) and PPT was higher (P < .0001; 31.5%-44.2%; d = 1.03-1.8) for lower versus upper body locations. CONCLUSIONS: Health professionals and the public can be assured of similar reductions in pain sensitivity independent of the location of application of a menthol-based topical analgesic.

Effect of an inverted seated position with upper arm blood flow restriction on measures of elbow flexors neuromuscular performance.

PURPOSE: The objective of the investigation was to determine the concomitant effects of upper arm blood flow restriction (BFR) and inversion on elbow flexors neuromuscular responses. METHODS: Randomly allocated, 13 volunteers performed four conditions in a within-subject design: rest (control, 1-min upright position without BFR), control (1-min upright with BFR), 1-min inverted (without BFR), and 1-min inverted with BFR. Evoked and voluntary contractile properties, before, during and after a 30-s maximum voluntary contraction (MVC) exercise intervention were examined as well as pain scale. RESULTS: Inversion induced significant pre-exercise intervention decreases in elbow flexors MVC (21.1%, [Formula: see text] = 0.48, p = 0.02) and resting evoked twitch forces (29.4%, [Formula: see text] = 0.34, p = 0.03). The 30-s MVC induced significantly greater pre- to post-test decreases in potentiated twitch force ([Formula: see text] = 0.61, p = 0.0009) during inversion (↓75%) than upright (↓65.3%) conditions. Overall, BFR decreased MVC force 4.8% ([Formula: see text] = 0.37, p = 0.05). For upright position, BFR induced 21.0% reductions in M-wave amplitude ([Formula: see text] = 0.44, p = 0.04). There were no significant differences for electromyographic activity or voluntary activation as measured with the interpolated twitch technique. For all conditions, there was a significant increase in pain scale between the 40-60 s intervals and post-30-s MVC (upright

Periodized versus Non-periodized Stretch Training on Gymnasts Flexibility and Performance.

Static stretching (SS) can increase joint range of motion (ROM), due to neural, morphological, and physio-psychological factors. Periodized training programs (PD) (e. g., strength, power) are adopted to induce greater adaptations while avoiding overtraining. However, the effectiveness of periodized stretch training adaptations are unknown. Therefore, the objective of this study was to compare the effects of periodized and non-periodized (NP) stretching programs on flexibility, hamstrings stiffness and muscle performance. Sixteen gymnasts were allocated to either periodized or non-periodized SS training and tested pre- and post-8 weeks for countermovement jump height, hip flexors, hip extensors and dorsiflexors ROM, hamstrings stiffness and hamstrings and quadriceps peak torque. Both stretch training groups significantly and similarly increased hip extensor (33.2%), hip flexor (25.2%), and dorsiflexor (23.8%) ROM, hamstrings peak torque (7.9%) and jump height (8.1%) from pre - to post- training. Both groups decreased hamstrings stiffness across the last ten angles (32.1%). PD elicited consistently large magnitude flexibility effect size changes compared to small and moderate magnitude changes for the non-periodized. Therefore, 8-week PD and NP SS programs can decrease young gymnasts' muscle-tendon stiffness and increase muscle performance. However, effect sizes indicate that PD stretch training was more advantageous to increasing flexibility and improving performance.

Superior Training-Specific Adaptations With an 8-Week Yoak Push-up Training Program.

Lima, C, Li, Y, Low, JL, Herat, N, and Behm, DG. Superior training-specific adaptations with an 8-week yoak push-up training program. J Strength Cond Res 32(9): 2409-2418, 2018-There are few progressive metastability training programs in the literature. The purpose of this study was to investigate changes in strength, endurance, muscle activation, and neuromuscular efficiency after an 8-week progressive, push-up training program under stable and unstable conditions. Nineteen male and female recreationally trained participants performed twice per week, an 8-week push-up training program, using either a relatively unstable suspension system (Yoak) or under stable conditions. Participants were tested in 2 separate sessions before and after training for chest press maximal voluntary isometric contraction (MVIC) forces, and unstable and stable push-up endurance. Participants were tested during all testing measures for anterior deltoid, biceps brachii (BB), triceps brachii (TB), and serratus anterior (SA) electromyography (EMG) activity. The training progression consisted of altering the suspension configurations, push-up height, and increasing the number of sets (1-3 sets). The stable group performed 153.3 and 33.8% less repetitions than the Yoak group when performing push-ups on the Yoak device or stable floor, respectively (p = 0.03). Training-induced MVIC forces were 9.2% (p = 0.03) greater for the Yoak vs. the stable group. Regarding neuromuscular efficiency, the Yoak group decreased (30.4%; p = 0.01) and stable group increased (97.8%; p = 0.02) antagonist BB EMG activity from pre- to post-training. Both groups decreased the TB fatigue index from pre- to post-training. Nevertheless, Yoak group demonstrated 12.5% (p = 0.09) and 8.9% (p = 0.02) lower fatigue indexes with TB and SA, respectively, than the stable group. These findings suggest that Yoak training demonstrates superior improvements over stable training for push-up endurance, neuromuscular efficiency, MVIC, and fatigue index.

Knowledge of Repetition Range Does Not Affect Maximal Force Production Strategies of Adolescent Females.

PURPOSE: Contrary to adult force reserve strategies, it is not known whether adolescent females with less experience performing maximal voluntary contractions (MVC) have specific responses to a known or unknown fatigue endpoint. METHODS: Using a counterbalanced random crossover design, fourteen inexperienced female adolescents completed three elbow flexor (EF) fatiguing protocols. Participants were randomly assigned to a control (informed they would perform 12 MVCs), unknown (not informed of the number of MVCs to be completed, but stopped after 12) or deception condition (instructed to complete 6 MVCs, however, after the sixth repetition performed another 6 MVCs). Before and during the interventions, EF impulse, force, and biceps brachii (BB) and triceps brachii (TB) electromyography (EMG) activity were recorded. RESULTS: Participants exhibited decreases in impulse (10.9%; p < .05), force (7.5%; p = .001), BB (16.2%; p < .05) and TB (12.9%; p < .05) EMG activity between the pretest and the first repetition of all protocols. Knowledge of endpoint, or lack of it, did not change measures with the repeated MVCs. When informed about the final repetition, force remained depressed suggesting no physiological reserve. CONCLUSION: Adolescent females exhibited an anticipatory response to the task of performing repeated MVCs. A lack of change with knowledge of endpoint indicates that those lacking in MVC experience do not employ the same pacing strategies as in previous studies of participants with MVC experience.

Knowledge of Repetition Range Does Not Affect the Maximal Force Production Strategies of Adolescent Females.

PURPOSE: Contrary to adult force reserve strategies, it is not known whether adolescent females with less experience performing maximal voluntary contractions (MVC) have specific responses to a known or unknown fatigue endpoint. METHODS: Using a counterbalanced random crossover design, fourteen inexperienced female adolescents completed three elbow flexor (EF) fatiguing protocols. Participants were randomly assigned to a control (informed they would perform 12 MVCs), unknown (not informed of the number of MVCs to be completed, but stopped after 12) or deception condition (instructed to complete 6 MVCs, however, after the 6th repetition performed another 6 MVCs). Before and during the interventions, EF impulse, force, and biceps brachii (BB) and triceps brachii (TB) electromyography (EMG) activity were recorded. RESULTS: Participants exhibited decreases in impulse (10.9%; p<0.05), force (7.5%; p=0.001), BB (16.2%; p<0.05) and TB (12.9%; p<0.05) EMG activity between the pre-test and the first repetition of all protocols. Knowledge of endpoint, or lack of it, did not change measures with the repeated MVCs. When informed about the final repetition, force remained depressed suggesting no physiological reserve. CONCLUSION: Adolescent females exhibited an anticipatory response to the task of performing repeated MVCs. A lack of change with knowledge of endpoint indicates that those lacking in MVC experience do not employ the same pacing strategies as in previous studies of participants with MVC experience.