Changes in joint angle,muscle‐tendon complex length,muscle contractile tissue displacement,and modulation of EMG activity during acute whole‐body vibration

It has been suggested that vibration causes small changes in muscle length, but to the best of our knowledge, these have yet to be demonstrated during whole‐body vibration (WBV). This was an observational study to determine whether acute WBV would result in muscle lengthening. We hypothesized that acute WBV would increase electromyography (EMG) activity concurrently with measurable changes in muscle contractile length. Nine healthy males performed two conditions on a Galileo vibration machine for 15 s at 0 HZ (resting) and 6 HZ at a set knee angle of 18°. Muscle tendon complex length, contractile tissue displacement of the medial gastrocnemius muscle, and EMG of soleus, tibialis anterior, and vastus lateralis muscles were measured. At 6 HZ the medial gastrocnemius (MG) muscle tendon complex (MTC) amplitude (375 μm) was significantly greater (P < 0.05) compared to 0 HZ (35 μm). The MG contractile length (CD) amplitude at 6 HZ (176 μm) was significantly greater (P < 0.01) compared to 0 HZ (4 μm). Significant increases (P < 0.05) in EMG modulation were found for all muscles during the 6 HZ compared to the 0 HZ condition. The major finding was that ≈50% of the elongation occurred within the muscle itself and was associated with preceding changes in EMG. This indicates muscle lengthening may be a prerequisite for eliciting stretch reflexes. In conclusion, there is a temporal association between EMG activity and muscle contractile tissue displacement where low‐frequency WBV results in small muscle length changes and increases muscle activation. Muscle Nerve, 2009     

Lack of caspase‐3 attenuates immobilization‐induced muscle atrophy and loss of tension generation along with mitigation of apoptosis and inflammation

Introduction: Immobilization by casting induces disuse muscle atrophy (DMA). Methods: Using wild type (WT) and caspase‐3 knockout (KO) mice, we evaluated the effect of caspase‐3 on muscle mass, apoptosis, and inflammation during DMA. Results: Caspase‐3 deficiency significantly attenuated muscle mass decrease [gastrocnemius: 28 ± 1% in KO vs. 41 ± 3% in WT; soleus: 47 ± 2% in KO vs. 56 ± 2% in WT; (P < 0.05)] and gastrocnemius twitch tension decrease (23 ± 4% in KO vs. 36 ± 3% in WT, P < 0.05) at day 14 in immobilized vs. contralateral hindlimb. Lack of caspase‐3 decreased immobilization‐induced increased apoptotic myonuclei (3.2‐fold) and macrophage infiltration (2.2‐fold) in soleus muscle and attenuated increased monocyte chemoattractant protein‐1 mRNA expression (2‐fold in KO vs. 18‐fold in WT) in gastrocnemius. Conclusions: Caspase‐3 plays a key role in DMA and associated decreased tension, presumably by acting on the apoptosis and inflammation pathways. Muscle Nerve 47: 711–721, 2013     

Effects of moderate‐ and high‐intensity chronic exercise on brain‐derived neurotrophic factor expression in fast and slow muscles

Introduction: Brain‐derived neurotrophic factor (BDNF) protein expression is sensitive to cellular activity. In the sedentary state, BDNF expression is affected by the muscle phenotype. Methods: Eighteen Wistar rats were divided into the following 3 groups: sedentary (S); moderate‐intensity training (MIT); and high‐intensity training (HIT). The training protocol lasted 8 weeks. Forty‐eight hours after training, total RNA and protein levels in the soleus and plantaris muscles were obtained. Results: In the plantaris, the BDNF protein level was lower in the HIT than in the S group (P < 0.05). A similar effect was found in the soleus (without significant difference). In the soleus, higher Bdnf mRNA levels were found in the HIT group (P < 0.001 vs. S and MIT groups). In the plantaris muscle, similar Bdnf mRNA levels were found in all groups. Conclusions: These results indicate that high‐intensity chronic exercise reduces BDNF protein level in fast muscles and increases Bdnf mRNA levels in slow muscles. Muscle Nerve 53: 446–451, 2016     

Repetitive stretch suppresses denervation‐induced atrophy of soleus muscle in rats

This study was conducted to examine whether stretch‐related mechanical loading on skeletal muscle can suppress denervation‐induced muscle atrophy, and if so, to depict the underlying molecular mechanism. Denervated rat soleus muscle was repetitively stretched (every 5 s for 15 min/day) for 2 weeks. Histochemical analysis showed that the cross‐sectional area of denervated soleus muscle fibers with repetitive stretching was significantly larger than that of control denervated muscle (P < 0.05). We then examined the involvement of the Akt/mammalian target of the rapamycin (mTOR) cascade in the suppressive effects of repetitive stretching on muscle atrophy. Repetitive stretching significantly increased the Akt, p70S6K, and 4E‐BP1 phosphorylation in denervated soleus muscle compared to controls (P < 0.05). Furthermore, repetitive stretching‐induced suppression of muscle atrophy was fully inhibited by rapamycin, a potent inhibitor of mTOR. These results indicate that denervation‐induced muscle atrophy is significantly suppressed by stretch‐related mechanical loading of the muscle through upregulation of the Akt/mTOR signal pathway. Muscle Nerve, 2009     

Mitochondrial function following downhill and/or uphill exercise training in rats

Introduction: The goal of this study was to compare the effects of downhill (DH), uphill (UH), and UH‐DH exercise training, at the same metabolic rate, on exercise capacity and skeletal muscle mitochondrial function. Methods: Thirty‐two Wistar rats were separated into a control and 3 trained groups. The trained groups exercised for 4 weeks, 5 times per week at the same metabolic rate, either in UH, DH, or combined UH‐DH. Twenty‐four hours after the last training session, the soleus, gastrocnemius, and vastus intermedius muscles were removed for assessment of mitochondrial respiration. Results: Exercise training, at the same metabolic rate, improved maximal running speed without specificity for exercise modalities. Maximal fiber respiration was enhanced in soleus and vastus intermedius in the UH group only. Conclusions: Exercise training, performed at the same metabolic rate, improved exercise capacity, but only UH‐trained rats enhanced mitochondrial function in both soleus and vastus intermedius skeletal muscle. Muscle Nerve 54 : 925–935, 2016     

Physical exercise during muscle regeneration improves recovery of the slow/oxidative phenotype

Introduction: As skeletal muscle mass recovery after extensive injury is improved by contractile activity, we explored whether concomitant exercise accelerates recovery of the contractile and metabolic phenotypes after muscle injury. Methods: After notexin‐induced degeneration of a soleus muscle, Wistar rats were assigned to active (running exercise) or sedentary groups. Myosin heavy chains (MHC), metabolic enzymes, and calcineurin were studied during muscle regeneration at different time points. Results: The mature MHC profile recovered earlier in active rats (21 days after injury) than in sedentary rats (42 days). Calcineurin was higher in the active degenerated than in the sedentary degenerated muscles at day 14. Citrate synthase and total lactate dehydrogenase (LDH) activity decreased after injury and were similarly recovered in both active and sedentary groups at 14 or 42 days, respectively. H‐LDH isozyme activity recovered earlier in the active rats. Conclusions: Exercise improved recovery of the slow/oxidative phenotype after soleus muscle injury. Muscle Nerve 55 : 91–100, 2017     

Muscle imaging analogies in a cohort of patients with different clinical phenotypes caused by LMNA gene mutations

Laminopathies are a heterogeneous group of LMNA‐gene‐mutation–related clinical disorders associated with alterations of cardiac and skeletal muscle and peripheral nerves, metabolic defects, and premature aging. Leg muscle imaging investigations were performed in a cohort of patients with LMNA gene alterations who were suffering from Emery–Dreifuss muscular dystrophy, limb‐girdle muscular dystrophy type 1B, isolated cardiac disorders or a phenotype of cardiac disorders, and lipodystrophy, including one individual with peripheral neuropathy. Leg muscle imaging revealed varying degrees of alteration in the soleus and medial head of gastrocnemius in each subject. This study demonstrates that LMNA‐gene‐mutated patients devoid of any clinically detectable skeletal muscle involvement have the same pattern of leg muscle involvement as patients with overt skeletal muscle compromise. This finding suggests the presence of a continuum of skeletal muscle involvement among phenotypes of LMNA‐gene‐mutation–related skeletalmyopathy and cardiomyopathy. Muscle Nerve, 2010     

Paraplegia increases skeletal muscle autophagy

Introduction: Paraplegia results in significant skeletal muscle atrophy through increases in skeletal muscle protein breakdown. Recent work has identified a novel SIRT1–p53 pathway that is capable of regulating autophagy and protein breakdown. Methods: Soleus muscle was collected from 6 male Sprague‐Dawley rats 10 weeks after complete T4–5 spinal cord transection (paraplegia group) and 6 male sham‐operated rats (control group). We utilized immunoblotting methods to measure intracellular proteins and quantitative real‐time polymerase chain reaction to measure the expression of skeletal muscle microRNAs. Results: SIRT1 protein expression was 37% lower, and p53 acetylation (LYS379) was increased in the paraplegic rats (P < 0.05). Atg7 and Beclin‐1, markers of autophagy induction, were elevated in the paraplegia group compared with controls (P < 0.05). Conclusions: Severe muscle atrophy resulting from chronic paraplegia appears to increase skeletal muscle autophagy independent of SIRT1 signaling. We conclude that chronic paraplegia may cause an increase in autophagic cell death and negatively impact skeletal muscle protein balance. Muscle Nerve 46: 793–798, 2012     

Elicitability of muscle cramps in different leg and foot muscles

To explore the efficacy of muscle motor point stimulation in eliciting muscle cramps, 11 subjects underwent eight sessions of electrical stimulation of the following muscles bilaterally: abductor hallucis flexor hallucis brevis, and both heads of the gastrocnemius muscles. Bursts of 150 square wave stimuli (duration: 152 μs; current intensity: 30% supramaximal) were applied. The stimulation frequency was increased from 4 pulses per second (pps) at increments of 2 pps until a cramp was induced. The number of cramps that could be elicited was smaller in flexor hallucis brevis than in abductor hallucis (16 vs. 22 out of 22 trials each; P < 0.05) and in the lateral gastrocnemius than in the medial gastrocnemius (5 vs. 20 out of 22 trials each; P < 0.0001). We show that leg and foot muscles have different cramp susceptibility, and the intermuscle variability in the elicitability profile for electrically induced cramps supports the use of the proposed method for cramp research. Muscle Nerve, 2009     

Diffusion tensor MRI to assess skeletal muscle disruption following eccentric exercise

Introduction: Structural evidence of exercise‐induced muscle disruption has traditionally involved histological analysis of muscle tissue obtained by needle biopsy, however, there are multiple limitations with this technique. Recently, diffusion tensor magnetic resonance imaging (DT‐MRI) has been successfully demonstrated to noninvasively assess skeletal muscle abnormalities induced by traumatic injury. Methods: To determine the potential for DT‐MRI to detect musculoskeletal changes after a bout of eccentric exercise, 10 healthy men performed 300 eccentric actions on an isokinetic dynamometer. DT‐MRI measurements and muscle biopsies from the vastus lateralis were obtained before and 24 h post‐exercise. Results: Z‐band streaming was higher 24 h post‐exercise compared with baseline (P < 0.05). The histological indices of damage coincided with changes in DT‐MRI parameters of fractional anisotropy (FA) and apparent diffusion coefficient; reflecting altered skeletal muscle geometry (P < 0.05). Z‐band streaming quantified per fiber correlated with FA (r = ?0.512; P < 0.05). Conclusions: DT‐MRI can detect changes in human skeletal muscle structure following eccentric exercise. Muscle Nerve 46: 42–50, 2012     

Serum brain‐derived neurotrophic factor and interleukin‐6 response to high‐volume mechanically demanding exercise

Introduction: The aim of this study was to follow circulating brain‐derived neurotrophic factor (BDNF) and interleukin‐6 (IL‐6) levels in response to severe muscle‐damaging exercise. Methods: Young healthy men (N = 10) performed a bout of mechanically demanding stretch–shortening cycle exercise consisting of 200 drop jumps. Voluntary and electrically induced knee extension torque, serum BDNF levels, and IL‐6 levels were measured before and for up to 7 days after exercise. Results: Muscle force decreased by up to 40% and did not recover by 24 hours after exercise. Serum BDNF was decreased 1 hour and 24 hours after exercise, whereas IL‐6 increased immediately and 1 hour after but recovered to baseline by 24 hours after exercise. IL‐6 and 100‐Hz stimulation torque were correlated (r = ?0.64, P < 0.05) 24 hours after exercise. Discussion: In response to acute, severe muscle‐damaging exercise, serum BDNF levels decrease, whereas IL‐6 levels increase and are associated with peripheral fatigue. Muscle Nerve 57 : E46–E51, 2018     

Differential regulation by exercise of BDNF and NT-3 in rat spinal cord and skeletal muscle

We have investigated the impact of neuromuscular activity on the expression of neurotrophins in the lumbar spinal cord region and innervating skeletal muscle of adult rats. Rats were exercised on a treadmill for 1 day or 5 consecutive days and euthanized at 0, 2 or 6 h after the last bout of exercise. By Day 1, there was no clear evidence of an increase in brain-derived neurotrophic factor (BDNF) mRNA in the spinal cord or the soleus muscle. By Day 5, there was a significant increase in BDNF mRNA in the spinal cord at 2 h post-training, and the soleus muscle showed a robust increase between 0 and 6 h post-training. Immunoassays showed significant increases in BDNF protein in the soleus muscle by training Day 5. Immunohistochemical analyses showed elevated BDNF levels in motoneuron cell bodies and axons in the ventral horn. Neurotrophin-3 (NT-3) mRNA was measured to determine whether selected neurotrophins respond with a selective pattern of induction to neuromuscular activity. In the spinal cord, there was a progressive post-training decrease in NT-3 mRNA following a single bout of training, while there was a significant increase in NT-3 mRNA at 2 h post-training by Day 5. The soleus muscle showed a progressive increase in NT-3 mRNA by Days 1 and 5 following training. These results show that neuromuscular activity has specific effects on the BDNF and NT-3 systems, and that repetitive exercise affects the magnitude and stability of these responses.     

Low‐volume resistance exercise attenuates the decline in strength and muscle mass associated with immobilization

We determined the effectiveness of low‐volume resistance exercise (EX) for the attenuation of loss of muscle mass and strength during leg immobilization. Men (N = 5) and women (N = 12, age 24 ± 5 years, body mass index 25.4 ± 3.6 kg/m²) were divided into two groups: exercise (EX; n = 12) and control (CON; n = 5). Subjects wore a knee brace on one leg that prevented weight bearing for 14 days. Resistance exercise (EX; 80% of maximal) was performed by the immobilized limb every other day. Immobilization induced a significant reduction (P < 0.05) in muscle fiber and thigh cross‐sectional area (CSA), isometric knee extensor, and plantarflexor strength in the CON (P < 0.01) but not in the EX group. There were significant losses in triceps surae CSA in the CON and EX groups (P < 0.05), but the losses were greater in CON subjects (P < 0.01). A minimal volume (140 contractions in 14 days) of resistive exercise is an effective countermeasure against immobilization‐induced atrophy of the quadriceps femoris but is only partially effective for the triceps surae. Muscle Nerve, 2010     

Soleus and lateral gastrocnemius H‐reflexes during standing with unstable footwear

Introduction: Unstable footwear has been shown to increase lower extremity muscle activity, but the reflex response to perturbations induced by this intervention is unknown. Methods: Twenty healthy subjects stood in stable and unstable footwear conditions (presented randomly) while H‐reflex amplitude and background muscle activity were measured in the soleus and lateral gastrocnemius (LG) muscles. Results: Wearing unstable footwear resulted in larger H‐reflexes (normalized to the maximal M‐wave) for the LG (+12%; P = 0.025), but not for the soleus (+4%; P > 0.05). Background activity of both muscles was significantly higher in the unstable condition. Conclusions: The H‐reflex facilitation observed with unstable footwear was unexpected, as challenging postural conditions usually result in reflex depression. Increased muscle activity, decreased presynaptic inhibition, and/or more forward postural position may have (over‐)compensated the expected reflex depression. Differences between LG and soleus H‐reflex modulation may be due to diverging motor unit recruitment thresholds. Muscle Nerve 51 :764–766, 2015     

Apigenin inhibits sciatic nerve denervation–induced muscle atrophy

Introduction: Apigenin (AP) has been reported to elicit anti‐inflammatory effects. In this study, we investigated the effect of AP on sciatic nerve denervation–induced muscle atrophy. Methods: Sciatic nerve–denervated mice were fed a 0.1% AP‐containing diet for 2 weeks. Muscle weight and cross‐sectional area (CSA), and the expression of atrophic genes and inflammatory cytokines in the gastrocnemius were analyzed. Results: Denervation significantly induced muscle atrophy. However, values for muscle weight and CSA were greater in the denervated muscle of the AP mice than the controls. AP suppressed the expression of MuRF1, but upregulated both myosin heavy chain (MHC) and MHC type IIb. AP also significantly suppressed expression of tumor necrosis‐alpha in the gastrocnemius and soleus muscles, and interleukin‐6 expression in the soleus muscle. Discussion: AP appears to inhibit denervation‐induced muscle atrophy, which may be due in part to its inhibitory effect on inflammatory processes within muscle. Muscle Nerve 58 : 314–318, 2018     

Muscle histopathology in children with spastic cerebral palsy receiving botulinum toxin type A

Introduction: Botulinum toxin A (BoNTA) is routine treatment for hypertonicity in children with cerebral palsy (CP). Methods: This single‐blind, prospective, cross‐sectional study of 10 participants (mean age 11 years 7 months) was done to determine the relationship between muscle histopathology and BoNTA in treated medial gastrocnemius muscle of children with CP. Open muscle biopsies were taken from medial gastrocnemius muscle and vastus lateralis (control) during orthopedic surgery. Results: Neurogenic atrophy in the medial gastrocnemius was seen in 6 participants between 4 months and 3 years post‐BoNTA. Type 1 fiber loss with type 2 fiber predominance was significantly related to the number of BoNTA injections (r = 0.89, P < 0.001). Conclusions: The impact of these changes in muscle morphology on muscle function in CP is not clear. It is important to consider rotating muscle selection or injection sites within the muscle or allowing longer time between injections. Muscle Nerve 53: 407–414, 2016     

Reliability of panoramic ultrasound imaging to simultaneously examine muscle size and quality of the medial gastrocnemius

Introduction: In this study we examined the test–retest reliability of panoramic brightness‐mode ultrasound (US) imaging to simultaneously measure both muscle size and quality from a single US image. Methods: Sixteen healthy, recreationally active men (age = 20.9 ± 2.5 years) volunteered for this investigation. Test–retest reliability was evaluated using intraclass correlation coefficients (ICCs) and the standard error of measurement as a percentage of the mean (SEM%). Muscle size [cross‐sectional area (CSA)], and muscle quality [echo intensity (EI)] of the medial gastrocnemius were examined on 2 separate days. Results: These measures demonstrated acceptable reliability between assessment days with ICCs and SEM% of 0.914 and 0.720 and 5.830 and 3.680 for CSA and EI, respectively. Conclusions: These results suggest that panoramic US imaging may be a reliable technique for simultaneous assessment of both muscle size and quality from a single US scan. Muscle Nerve 49 : 736–740, 2014     

Post‐activation potentiation: The neural effects of post—activation depression

Introduction: Our knowledge of the neurophysiology of post‐activation potentiation (PAP) is limited. The purpose of this study was to examine the effect of PAP on twitch torque and H‐reflex amplitude after a 10‐s maximal voluntary contraction (MVC). Methods: PAP measurements were assessed with the plantarflexors in a relaxed state and during a tonic contraction at 10% MVC. Results: The H‐reflex/maximum M‐wave ratio (H/M) decreased significantly (P < 0.05) and returned to baseline levels after 1 min. The decrement in H/M was depressed when the plantarflexors were active at 10% MVC, and the depression was more obvious in the lateral gastrocnemius than in the soleus muscle. Conclusions: The inhibition induced immediately after contraction could be attributed to post‐activation depression. We conclude that PAP after a 10‐s MVC cannot be attributed to increased motor neuron excitability through the reflex pathway as assessed by the H‐reflex technique. Muscle Nerve 52 : 252–259, 2015