Causes of excitation-induced muscle cell damage in isometric contractions: mechanical stress or calcium overload?

Nelumbinis Stamen Ameliorates Chronic Restraint Stress-Induced Muscle Dysfunction and Fatigue in Mice by Decreasing Serum Corticosterone Levels and Activating Sestrin2

Nelumbo nucifera Gaertn. is an important aquatic vegetable, and its dried stamen (Nelumbinis stamen, NS) is a valuable nutraceutical usually used as a herbal tea. Here, we used ultrahigh-performance liquid chromatography (UPLC)-quadrupole time-of-flight mass spectrometry and high-performance liquid chromatography (HPLC) to chemically profile NS and quantify their main constituent flavonoids, respectively. In total, 44 components were identified, including organic acids, flavonoids, monoterpene glycosides, and fatty acids. Experimental mice were induced with fatigue by exposure to chronic restraint stress (CRS) for 8 h daily for 15 days and then treated with an aqueous extract of NS (0.5 and 1 g/kg) via gavage. NS significantly mitigated CRS-induced skeletal muscle dysfunction and fatigue in mice possibly by lowering serum corticosterone levels and restoring Sestrin2 expression in the gastrocnemius to regulate metabolism, preserve mitochondrial homeostasis, and promote antioxidant capacity. These results demonstrate that NS can be used as a nutraceutical or supplement for controlling stress-induced muscle dysfunction and fatigue.

Photobiomodulation Therapy Does Not Attenuate Fatigue and Muscle Damage in Judo Athletes: A Randomized, Triple-Blind, Placebo-Controlled Trial

Fatigue and muscle damage negatively affect performance in lower limb exercises involving the stretch-shortening cycle in judo athletes during competition and training sessions. Photobiomodulation therapy has emerged as an effective non-invasive strategy to attenuate fatigue and muscle damage when applied before different types of exercises. Our objective was to investigate the effects of photobiomodulation therapy on fatigue and muscle damage in judo athletes. Sixteen judo athletes participated in the study (23.1 ± 3.8 years, 77.9 ± 14.9 kg, 173.1 ± 8.9 cm, 17.5 ± 7.3 body fat%, 12.9 ± 5.0 years of practice). Each participant received, in a randomized manner, photobiomodulation in one limb and placebo in the contralateral limb on the same day. Thereafter, subjects performed a stretch-shortening cycle protocol to induce muscle fatigue and damage. Countermovement jump (impulse, peak power, peak velocity, and peak force), echo intensity (rectus femoris and vastus lateralis), and muscle soreness were assessed at different time points before, during, immediately post, and 24 and 48 h after the protocol. Muscle fatigue was detected due to reductions in countermovement jump impulse (14.7 ± 9.8 and 15.9 ± 15.5%), peak power (12.9 ± 8.5 and 11.9 ± 6.9%), peak velocity (8.6 ± 8.1 and 6.5 ± 6.0%), and peak force (7.0 ± 5.3 and 8.0 ± 6.1%) after the protocol (p < 0.001), for placebo and photobiomodulation therapy, respectively. Muscle damage was detected due to reductions in countermovement jump impulse (−6.1 ± 19.2% and −4.5 ± 9.2%, p < 0.05), increases in echo intensity (rectus femoris, 21.0 ± 11.9 and 20.8 ± 9.0%; and vastus lateralis, 22.4 ± 23.2%; and 16.7 ± 23.8%; p < 0.001), and quadriceps muscle soreness (3.6 ± 1.6 and 3.5 ± 1.7 a.u; p < 0.011), 48 h after the protocol, for placebo and photobiomodulation therapy, respectively. No differences were observed between photobiomodulation therapy and placebo at any time points for any variables (p > 0.05), indicating no positive effect favoring photobiomodulation therapy. In conclusion, our findings suggest no effect of photobiomodulation therapy applied before exercise to reduce lower limb muscle fatigue and damage during and following a stretch-shortening cycle protocol in judo athletes.

Cold water immersion or LED therapy after training sessions: effects on exercise-induced muscle damage and performance in rats

Cryotherapy and phototherapy have been suggested as recovery methods due to their anti-inflammatory effects. They may also induce mitochondrial biogenesis, thus favoring endurance training adaptation. The aim of this study was to evaluate the anti-inflammatory and ergogenic effects of phototherapy or cold water immersion (CWI) applied daily after exercise in rats. Thirty-five rats were divided into five groups: control (CO), non-exercised (CE), passive recovery (PR), cold water immersion (CWI), and LED therapy (LED). The CO and CE groups were not submitted to training; however, the CE were submitted to an exhaustion test after the training period. Low-intensity swimming training (21 sessions, 45 min) was performed followed by passive recovery (PR), CWI (10 °C, 5 min), or infrared irradiation (940 nm, 4 J/cm²). Forty-eight hours after the final training session, the CE, PR, CWI, and LED animals were submitted to an exhaustion test. The animals were euthanized 24 h later and submitted to hematological, creatine kinase (CK), and C-reactive protein (PCR) analysis. Gastrocnemius and soleus muscles were submitted to histological analysis. No differences in blood cell counts, CK, and PCR were detected between groups. The CE group presented an increased number of areas with necrosis in the gastrocnemius and soleus muscles. The PR group presented the highest frequency of areas with edema and inflammation followed by CWI and LED groups. None of the recovery methods improved the performance in the exhaustion test. Successive applications of recovery methods do not improve exercise performance, but downmodulate the inflammation and prevent muscle necrosis.

Human skeletal muscle plasmalemma alters its structure to change its Ca2+-handling following heavy-load resistance exercise

High-force eccentric exercise results in sustained increases in cytoplasmic Ca2+ levels ([Ca2+]cyto), which can cause damage to the muscle. Here we report that a heavy-load strength training bout greatly alters the structure of the membrane network inside the fibres, the tubular (t-) system, causing the loss of its predominantly transverse organization and an increase in vacuolation of its longitudinal tubules across adjacent sarcomeres. The transverse tubules and vacuoles displayed distinct Ca2+-handling properties. Both t-system components could take up Ca2+ from the cytoplasm but only transverse tubules supported store-operated Ca2+ entry. The retention of significant amounts of Ca2+ within vacuoles provides an effective mechanism to reduce the total content of Ca2+ within the fibre cytoplasm. We propose this ability can reduce or limit resistance exercise-induced, Ca2+-dependent damage to the fibre by the reduction of [Ca2+]cyto to help maintain fibre viability during the period associated with delayed onset muscle soreness.

Effects of low-level laser therapy applied before or after plyometric exercise on muscle damage markers: randomized, double-blind, placebo-controlled trial

Promising effects of phototherapy on markers of exercise-induced muscle damage has been already demonstrated in constant load or isokinetic protocols. However, its effects on more functional situations, such as plyometric exercises, and when is the best moment to apply this treatment (pre- or post-exercise) remain unclear. Therefore, the purpose of this study was to investigate the effect of low-level laser therapy (LLLT) before or after plyometric exercise on quadriceps muscle damage markers. A randomized, double-blinded, placebo-controlled trial was conducted with 24 healthy men, 12 at pre-exercise treatment group and 12 at post-exercise treatment group. Placebo and LLLT (810 nm, 200 mW per diode, 6 J per diode, 240 J per leg) were randomly applied on right/left knee extensor muscles of each volunteer before/after a plyometric exercise protocol. Muscular echo intensity (ultrasonography images), soreness (visual analogue scale - VAS), and strength impairment (maximal voluntary contraction - MVC) were assessed at baseline, 24, 48, and 72 h post-exercise. Legs treated with LLLT before or after exercise presented significantly smaller increments of echo intensity (values up to 1 %) compared to placebo treatments (increased up to ∼7 %). No significant treatment effect was found for VAS and MVC, although a trend toward better results on LLLT legs have been found for VAS (mean values up to 30 % lesser than placebo leg). In conclusion, LLLT applied before or after plyometric exercise reduces the muscle echo intensity response and possibly attenuates the muscle soreness. However, these positive results were not observed on strength impairment.

Muscle damage and repeated bout effect following blood flow restricted exercise

PURPOSE

Blood-flow restricted resistance exercise training (BFRE) is suggested to be effective in rehabilitation training, but more knowledge is required about its potential muscle damaging effects. Therefore, we investigated muscle-damaging effects of BFRE performed to failure and possible protective effects of previous bouts of BFRE or maximal eccentric exercise (ECC).

METHODS

Seventeen healthy young men were allocated into two groups completing two exercise bouts separated by 14 days. One group performed BFRE in both exercise bouts (BB). The other group performed ECC in the first and BFRE in the second bout. BFRE was performed to failure. Indicators of muscle damage were evaluated before and after exercise.

RESULTS

The first bout in the BB group led to decrements in maximum isometric torque, and increases in muscle soreness, muscle water retention, and serum muscle protein concentrations after exercise. These changes were comparable in magnitude and time course to what was observed after first bout ECC. An attenuated response was observed in the repeated exercise bout in both groups.

CONCLUSION

We conclude that unaccustomed single-bout BFRE performed to failure induces significant muscle damage. Additionally, both ECC and BFRE can precondition against muscle damage induced by a subsequent bout of BFRE.

Effect of low-level phototherapy on delayed onset muscle soreness: a systematic review and meta-analysis

To determine the effectiveness of low-level phototherapy (i.e. light-emitting diode therapy [LEDtherapy] or light amplification by stimulated emission of radiation therapy [LASERtherapy]) on pain, skeletal muscle injury (creatine kinase [CK] levels and edema) and skeletal muscle function (range of movement and strength) in people undergoing an exercise protocol. (Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, PEDro, SciELO and LILACS up to May 2014), we included randomized controlled trials, quasi-randomized controlled trials and crossover studies in which study participants were allocated to receive either low-level phototherapy or placebo treatment. Phototherapy should have been applied in a single treatment session, either before or after an exercise protocol. We identified 15 studies involving 317 participants. Meta-analyses were limited by substantial heterogeneity. Compared to the placebo group, reduction in CK levels was only observed when LASERtherapy was applied before an exercise protocol (standardized mean difference = -0.66; 95 % CI = -1.30, -0.02). No between-group difference in edema, range of movement and strength were detected when phototherapy was applied before or after exercise. Evidence from this review suggests that low-level phototherapy may not have substantial effect in the treatment of skeletal muscle injury and pain caused by exercise. Definitive conclusions are limited due to the small number of included studies in each meta-analysis, disparities across the included studies and small sample sizes.

Studies on the Antifatigue Activities of Cordyceps militaris Fruit Body Extract in Mouse Model

Cordyceps militaris has been used extensively as a crude drug and a folk tonic food in East Asia due to its various pharmacological activities. Our study aims to investigate the effect of Cordyceps militaris fruit body extract (CM) on antifatigue in mouse model. Two week CM administration significantly delayed fatigue phenomenon which is confirmed via rotating rod test, forced swimming test and forced running test. Compared to nontreated mouse, CM administration increased ATP levels and antioxidative enzymes activity and reduced the levels of lactic acid, lactic dehydrogenase, malondialdehyde, and reactive oxygen species. Further data suggests that CM-induced fatigue recovery is mainly through activating 5′-AMP-activated protein kinase (AMPK) and protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathways and regulating serum hormone level. Moreover, CM-enhanced the phosphorylation of AMPK contributes to its antioxidant effect. Our data provides experimental evidence in supporting clinical use of CM as an effective agent against fatigue.

Exhaustive exercise--a near death experience for skeletal muscle cells?

In sports medicine, muscle enzymes in the blood are frequently used as an indicator of muscle damage. It is commonly assumed that mechanical stress disrupts plasma membrane to an extent that allows large molecules, such as enzymes, to leak into the extracellular space. However, this does not appear to fully explain changes in muscle enzyme activity in the blood after exercise. Apart from this mechanically induced membrane damage, we hypothesize that, under critical metabolic conditions, ATP consuming enzymes like creatine kinase (CK) are "volitionally" expulsed by muscle cells in order to prevent cell death. This would put themselves into a situation comparable to that of CK deficient muscle fibers, which have been shown in animal experiments to be virtually infatigable at the expense of muscle strength. Additionally we expand on this hypothesis with the idea that membrane blebbing is a way for the muscle fibers to store CK in fringe areas of the muscle fiber or to expulse CK from the cytosol by detaching the blebs from the plasma membrane. The blebbing has been shown to occur in heart muscle cells under ischaemic conditions and has been speculated to be an alternative pathway for the expulsion of troponin. The blebbing has also been seen skeletal muscle cells when intracellular calcium concentration increases. Cytoskeletal damage, induced by reactive oxygen species (ROS) or by calcium activated proteases in concert with increasing intracellular pressure, seems to provoke this type of membrane reaction. If these hypotheses are confirmed by future investigations, our current understanding of CK as a blood muscle damage marker will be fundamentally affected.

Parvalbumin is overexpressed in the late phase of pharmacological preconditioning in skeletal muscle

Pharmacological preconditioning (PPC) with mitochondrial ATP-sensitive K(+) channel openers such as diazoxide, provides protection against ischemia in cardiac muscle, skeletal muscle, and other tissues. Effects on Ca(2+) homeostasis during the late phase of PPC have been described in cardiomyocytes, but no information is available regarding intracellular Ca(2+) changes in skeletal muscle fibers during late PPC. Intracellular Ca(2+) signals were measured in single fibers of adult mouse skeletal muscle, with fluorescent probes, 48 h after the administration of diazoxide. Parvalbumin levels in the myofibers were quantitated by Western blot. Diazoxide induction of late PPC was confirmed by partial protection of muscles from peroxide-induced damage. Late PPC was associated with a significant decrease in the duration of Ca(2+) signals during single twitches and tetanus with no changes in peak values. This effect was prevented by the reactive oxygen species (ROS) scavenger tiron. Late PPC was accompanied by a 30% increase in parvalbumin levels, and this effect was also blocked by tiron. Our data show, for the first time, a role of parvalbumin in late PPC in skeletal muscle.

Effects of β₂-agonists on force during and following anoxia in rat extensor digitorum longus muscle

Electrical stimulation of isolated muscles may lead to membrane depolarization, gain of Na(+), loss of K(+) and fatigue. These effects can be counteracted with β(2)-agonists possibly via activation of the Na(+)-K(+) pumps. Anoxia induces loss of force; however, it is not known whether β(2)-agonists affect force and ion homeostasis in anoxic muscles. In the present study isolated rat extensor digitorum longus (EDL) muscles exposed to anoxia showed a considerable loss of force, which was markedly reduced by the β(2)-agonists salbutamol (10(-6) M) and terbutaline (10(-6) M). Intermittent stimulation (15-30 min) clearly increased loss of force during anoxia and reduced force recovery during reoxygenation. The β(2)-agonists salbutamol (10(-7)-10(-5) M) and salmeterol (10(-6) M) improved force development during anoxia (25%) and force recovery during reoxygenation (55-262%). The effects of salbutamol on force recovery were prevented by blocking the Na(+)-K(+) pumps with ouabain or by blocking glycolysis with 2-deoxyglucose. Dibutyryl cAMP (1 mM) or theophylline (1 mM) also improved force recovery remarkably. In anoxic muscles, salbutamol decreased intracellular Na(+) and increased (86)Rb uptake and K(+) content, indicating stimulation of the Na(+)-K(+) pumps. In fatigued muscles salbutamol induced recovery of excitability. Thus β(2)-agonists reduce the anoxia-induced loss of force, leading to partial force recovery. These data strongly suggest that this effect is mediated by cAMP stimulation of the Na(+)-K(+) pumps and that it is not related to recovery of energy status (PCr, ATP, lactate).

Effects of light emitting diode (LED) therapy and cold water immersion therapy on exercise-induced muscle damage in rats

The aim of this work is to analyze the effects of LED therapy at 940 nm or cold water immersion therapy (CWI) after an acute bout of exercise on markers of muscle damage and inflammation. Thirty-two male Wistar rats were allocated into four groups: animals kept at rest (control), exercised animals (E), exercised + CWI (CWI), and exercised + LED therapy (LED). The animals swam for 100 min, after which blood samples were collected for lactate analysis. Animals in the E group were returned to their cages without treatment, the CWI group was placed in cold water (10°C) for 10 min and the LED group received LED irradiation on both gastrocnemius muscles (4 J/cm(2) each). After 24 h, the animals were killed and the soleus muscles were submitted to histological analysis. Blood samples were used for hematological and CK analyses. The results demonstrated that the LED group presented fewer areas of muscle damage and inflammatory cell infiltration and lower levels of CK activity than the E group. Fewer areas of damaged muscle fiber were observed in the LED group than in CWI. CWI and LED did not reduce edema areas. Hematological analysis showed no significant effect of either treatment on leukocyte counts. The results suggest that LED therapy is more efficient than CWI in preventing muscle damage and local inflammation after exercise.

Reduced soleus muscle injury at long muscle length during contraction in the rat

Muscle injury was studied to test the hypotheses that maintaining the soleus muscle at a long muscle length during contraction prevents muscle injuries and that the prevention of initial muscle injuries reduces subsequent muscle damage. The rat sciatic nerve was stimulated for 30 min with plantar or dorsal flexion of the foot, and the time course of contraction-induced injuries was examined. The soleus muscle injuries were first classified into one of five types, and the percentages of aberrant sarcomere areas observed in the soleus muscle were then separately quantified by electron microscopy at 0, 1, 6, 12, and 24 h (n = 3) post-stimulation. At a short muscle length (plantar flexion) during contraction, the soleus muscle showed sarcomere hypercontraction (9.8 ± 2.5%, mean ± standard error) and Z-band disarrangement (31.0 ± 4.5%) at 0 h, sarcomere hypercontraction (6.7 ± 1.9%), Z-band disarrangement (28.0 ± 4.9%), and sarcomere hyperstretching (1.3 ± 1.3%) at 1 h, the absence of sarcomere hypercontraction, but Z-band disarrangement (6.7 ± 1.9%) and sarcomere hyperstretching (5.0 ± 1.8%) at 6 h, and myofilament disorganization at 12 and 24 h (5.2 ± 1.5 and 2.5 ± 1.0%, respectively). In contrast, the soleus muscles at a long muscle length (dorsal flexion) during contraction using a self-made brace showed alterations in 1.2-2.4% of sarcomeres at 0 h and afterwards. Desmin disappeared, and α-actinin immunostaining was weaker in areas of sarcomere hypercontraction, whereas dystrophin was always detected along the sarcoplasmic membrane, suggesting that the integrity of the sarcolemma was intact. These results indicate that initial and subsequent muscle injuries were significantly reduced at long muscle length during contraction, probably through the prevention of sarcomere hypercontraction, and that initial muscle injuries rapidly progress to other injuries or normal structure.

Role of Ca(2+) in injury-induced changes in sodium current in rat skeletal muscle

Characteristics of voltage-dependent sodium current recorded from adult rat muscle fibers in loose patch mode were rapidly altered following nearby impalement with a microelectrode. Hyperpolarized shifts in the voltage dependence of activation and fast inactivation occurred within minutes. In addition, the amplitude of the maximal sodium current decreased within 30 min of impalement. Impalement triggered a sustained elevation of intracellular Ca(2+). However, buffering Ca(2+) by loading fibers with AM-BAPTA did not affect the hyperpolarized shifts in activation and inactivation, although it did prevent the reduction in current amplitude. Surprisingly, the rise in intracellular Ca(2+) occurred even in the absence of extracellular Ca(2+). This result indicated that the injury-induced Ca(2+) increase came from an intracellular source, but it was not blocked by an inhibitor of release from the sarcoplasmic reticulum, which suggested involvement of mitochondria. Ca(2+) release from mitochondria triggered by carbonyl cyanide 3-chlorophenylhydrazone was sufficient to cause a reduction in sodium current amplitude but had little effect of the voltage dependence of activation and fast inactivation. Our data suggest the effects of muscle injury can be separated into a Ca(2+)-dependent reduction in amplitude and a largely Ca(2+)-independent shift in activation and fast inactivation. Together, the impalement-induced changes in sodium current reduce the number of sodium channels available to open at the resting potential and may limit further depolarization and thus promote survival of muscle fibers following injury.

Decompression to altitude: assumptions, experimental evidence, and future directions

Although differences exist, hypobaric and hyperbaric exposures share common physiological, biochemical, and clinical features, and their comparison may provide further insight into the mechanisms of decompression stress. Although altitude decompression illness (DCI) has been experienced by high-altitude Air Force pilots and is common in ground-based experiments simulating decompression profiles of extravehicular activities (EVAs) or astronauts' space walks, no case has been reported during actual EVAs in the non-weight-bearing microgravity environment of orbital space missions. We are uncertain whether gravity influences decompression outcomes via nitrogen tissue washout or via alterations related to skeletal muscle activity. However, robust experimental evidence demonstrated the role of skeletal muscle exercise, activities, and/or movement in bubble formation and DCI occurrence. Dualism of effects of exercise, positive or negative, on bubble formation and DCI is a striking feature in hypobaric exposure. Therefore, the discussion and the structure of this review are centered on those highlighted unresolved topics about the relationship between muscle activity, decompression, and microgravity. This article also provides, in the context of altitude decompression, an overview of the role of denitrogenation, metabolic gases, gas micronuclei, stabilization of bubbles, biochemical pathways activated by bubbles, nitric oxide, oxygen, anthropometric or physiological variables, Doppler-detectable bubbles, and potential arterialization of bubbles. These findings and uncertainties will produce further physiological challenges to solve in order to line up for the programmed human return to the Moon, the preparation for human exploration of Mars, and the EVAs implementation in a non-zero gravity environment.