Background Muscle strength loss following immobilisation has been predominantly attributed to rapid muscle atrophy. However, this cannot fully explain the magnitude of muscle strength loss, so changes in neuromuscular function (NMF) may be involved. Objectives We systematically reviewed literature that quantified changes in muscle strength, size and NMF following periods of limb immobilisation in vivo in humans. Methods Studies were identified following systematic searches, assessed for inclusion, data extracted and quality appraised by two reviewers. Data were tabulated and reported narratively. Results Forty eligible studies were included, 22 immobilised lower and 18 immobilised upper limbs. Limb immobilisation ranged from 12 h to 56 days. Isometric muscle strength and muscle size declined following immobilisation; however, change magnitude was greater for strength than size. Evoked resting twitch force decreased for lower but increased for upper limbs. Rate of force development either remained unchanged or slowed for lower and typically slowed for upper limbs. Twitch relaxation rate slowed for both lower and upper limbs. Central motor drive typically decreased for both locations, while electromyography amplitude during maximum voluntary contractions decreased for the lower and presented mixed findings for the upper limbs. Trends imply faster rates of NMF loss relative to size earlier in immobilisation periods for all outcomes. Conclusions Limb immobilisation results in non-uniform loss of isometric muscle strength, size and NMF over time. Different outcomes between upper and lower limbs could be attributed to higher degrees of central neural control of upper limb musculature. Future research should focus on muscle function losses and mechanisms following acute immobilisation. Registration PROSPERO reference: CRD42016033692.

S lateralis (VL) muscles, and VL muscle oxygenation status (near-infrared spectroscopy) were recorded during metronome-guided knee extension exercise. Nine healthy adults completed four trials exercising at contraction intensities of 35% (L) or 70% (H) of one-repetition maximum (1RM) in control (no vibration, Vb−) or vibrated condition (superimposed 10-Hz vibration-like stimulus, Vb+). Maximum voluntary contraction and 1RM were tested pre- and postexercise. Results: During 1RM tests, muscle dynamic strength (P = 0.02) and power (P = 0.05) were significantly higher during vibrated rather than nonvibrated trials, and strength was significantly higher post- than preexercise (P = 0.002), except during LVb− trial. Median spectral frequency of VL and RF EMG activity was significantly higher during postexercise than preexercise 1RM test in the vibration trials but unchanged in the control trials (P < 0.02). The rate of muscle deoxygenation was 58% faster during H than L exercise (P = 0.001), and vibration superimposition tended to speed muscle deoxygenation rate (P = 0.065, 36% effect size) particularly during L trials. Conclusion: Vibration superimposition during knee extension exercise at low contraction intensity enhanced muscle performance. This effect appears to result from adaptation of neural factors such as motor unit excitability (recruitment and firing frequency, conduction velocity of excitation) in response to sensory receptor stimulation. Muscle vibration may increase the training effects derived from light-to-moderate exercise....

This study was conducted to investigate whether the low-frequency (5-Hz) oscillatory vibration-like stimulus, purported to be delivered by exercising with Flexi-bar, acutely affects muscle activation and maximal voluntary contraction (MVC) force. Nine healthy men participated in 2 trials, separated by at least 1 week, during which 4 x 30-second sets of exercise were performed with either the Flexi bar or a Sham bar. Maximal voluntary contraction force for elbow flexion, elbow extension, and knee extension were measured before and after the exercise. Root-mean-square amplitude and median frequency of electromyography (EMG) signal were calculated for the first and last 10 seconds of each exercise set and during the MVCs from biceps brachii (BB), triceps brachii (TB), rectus femoris (RF), and vastus lateralis (VL) for each trial. Electromyography amplitude was significantly higher for all studied muscles during Flexi-bar than Sham-bar exercise (32-203%, p < 0.05). Median frequency of EMG power spectrum was significantly lower in arm (TB: -40 +/- 13%, p < 0.0001; BB: -32 +/- 25%, p = 0.015) but not in leg (RF: -12 +/- 18%; VL: +6 +/- 32%; p > 0.05) muscles during Flexi-bar compared with Sham-bar exercise. Knee extension MVC force significantly decreased after Flexi-bar exercise (-3 +/- 7%, p = 0.048) in parallel with reduced RF EMG amplitude (-8 +/- 5%, p = 0.04), but there were no acute residual effects on elbow flexion/extension MVC or arm and VL EMG muscle activity. Using Flexi bar during exercise provoked acute alterations in arm- and leg-muscle EMG parameters and maximum force-generating capacity, indicating greater fatigue development than when exercising with the Sham bar. The results of this study indicate that Flexi bar may therefore be used to impose a stronger training stimulus on the muscle during submaximal exercise.