Unaccustomed Eccentric Exercise Research Articles

Impaired microvascular reactivity after eccentric muscle contractions is not restored by acute ingestion of antioxidants or dietary nitrate

Unaccustomed eccentric exercise leads to impaired microvascular function but the underlying mechanism is unknown. In this study, we evaluated the role of oxidative stress and of nitric oxide (NO) bioavailability. Thirty young men and women performed eccentric contractions of the tibialis anterior (TA) muscle (ECC), with the contralateral leg serving as nonexercising control (CON). Participants were randomized into three groups ingesting an antioxidant cocktail (AO), beetroot juice (BR) or placebo 46 h postexercise. At baseline and 48 h postexercise, hyperemic responses to brief muscle contractions and 5 min of cuff occlusion were assessed bilaterally in the TA muscles using blood oxygen level dependent (BOLD) magnetic resonance imaging. Eccentric contractions resulted in delayed time‐to‐peak (~22%; P < 0.001), blunted peak (~21%; P < 0.001) and prolonged time‐to‐half relaxation (~12%, P < 0.001) in the BOLD response to brief contractions, with no effects of AO or BR, and no changes in CON. Postocclusive time‐to‐peak was also delayed (~54%; P < 0.001) in ECC, with no effects of AO or BR, and no changes in CON. Impaired microvascular reactivity after eccentric contractions is confined to the exercised tissue, and is not restored with acute ingestion of AO or BR. Impairments in microvascular reactivity after unaccustomed eccentric contractions may result from structural changes within the microvasculature that can diminish muscle blood flow regulation during intermittent activities requiring prompt adjustments in oxygen delivery.

Recovery From Unaccustomed Strenuous Exercise In Young And Older Endurance-trained Adults

There is a well-conceived notion that rate of recovery from strenuous exercise gets slower with advancing age. It is not clear whether older adults who exercise habitually and are apparently healthy demonstrate slower rates of recovery from unaccustomed eccentric exercise. PURPOSE: The aim of the present study was to determine if older adults who are physically active demonstrate slower rates of recovery from unaccustomed strenuous eccentric exercise compared with younger peers. METHODS: A total of 39 apparently healthy men and women were studied; young sedentary (n=10, 28±2 years), young endurance-trained (n=15, 27±2 years), and older endurance-trained (n=14, 58±2 years) groups. Subjects performed 45 min (15 min x 3 times with 5 min resting periods) of downhill running (at -16% gradient) at a speed corresponding with 65% of their maximal oxygen consumption. Visual analog pain scale, isometric muscular strength, joint range of motion (ROM), and serum myoglobin concentration were measured at baseline as well as 24h, 48h, and 72h after the downhill running protocol. RESULTS: Compared with baseline, pain scores of each muscle group were greater at 24h, 48h, and 72h in all 3 groups (p<0.05). Isometric muscular strengths decreased following downhill running (p<0.05), but the pattern of this response and recovery did not differ among the three groups. The ROM for hip extension decreased after downhill running (p<0.05), with the most pronounced decline seen in the young sedentary group. ROM gradually increased to baseline levels in all 3 groups. Serum myoglobin concentrations increased at 24h and returned to baseline values at 48h in both the young and older trained groups. CONCLUSION: The present findings are not consistent with the prevailing notion that older trained adults have a slower rate of recovery from strenuous exercise compared with young adults.

Eccentric Muscle Contractions: Risks and Benefits.

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as “Delayed-Onset Muscular Soreness” (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

(108) Bilateral Sensory Deficits and Widespread Hyperalgesia following Delayed Onset Muscle Soreness of the Quadriceps

Unaccustomed eccentric exercise leads to delayed onset muscle soreness (DOMS). While DOMS has been demonstrated to result in altered postural control which may result in further injury, very little is known about the somatosensory changes at the knee in presence of DOMS of the quadriceps. DOMS elicited in this muscle was hypothesized to result in bilateral induced mechanical hyperalgesia, measured via pressure pain threshold (PPT) and hypoesthesia, evidenced by deficits in both vibration perception threshold (VPT) and proprioception which was measured via threshold to detection of passive motion (TDPM). Thirty participants (15 males and 15 females) took part in the study. Eccentric exercise consisted of 10 sets of 10 maximum eccentric quadriceps contractions of the dominant knee. Assessments consisted of pain intensity, PPT, VPT and, TDPM at 3 different assessment time points: (1) pre-eccentric exercise; (2) immediately and (3) 48 hours after eccentric exercise. Pain intensity increased and PPT decreased at 48 hours. VPT increased ipsilaterally both immediately and 48 hours after exercise. TDPM increased on the ipsilateral side immediately and bilaterally at 48 hours. Females demonstrated greater impairment in TDPM than males at 48 hours. Widespread hyperalgesia, ipsilaterally impaired VPT and bilaterally impaired proprioception were demonstrated in the presence of DOMS. Athletes performing strenuous lower limb eccentric exercise in training leading to DOMS may experience increased pain and hypoesthesia which may predispose them to lower quarter joint trauma. Unaccustomed eccentric exercise leads to delayed onset muscle soreness (DOMS). While DOMS has been demonstrated to result in altered postural control which may result in further injury, very little is known about the somatosensory changes at the knee in presence of DOMS of the quadriceps. DOMS elicited in this muscle was hypothesized to result in bilateral induced mechanical hyperalgesia, measured via pressure pain threshold (PPT) and hypoesthesia, evidenced by deficits in both vibration perception threshold (VPT) and proprioception which was measured via threshold to detection of passive motion (TDPM). Thirty participants (15 males and 15 females) took part in the study. Eccentric exercise consisted of 10 sets of 10 maximum eccentric quadriceps contractions of the dominant knee. Assessments consisted of pain intensity, PPT, VPT and, TDPM at 3 different assessment time points: (1) pre-eccentric exercise; (2) immediately and (3) 48 hours after eccentric exercise. Pain intensity increased and PPT decreased at 48 hours. VPT increased ipsilaterally both immediately and 48 hours after exercise. TDPM increased on the ipsilateral side immediately and bilaterally at 48 hours. Females demonstrated greater impairment in TDPM than males at 48 hours. Widespread hyperalgesia, ipsilaterally impaired VPT and bilaterally impaired proprioception were demonstrated in the presence of DOMS. Athletes performing strenuous lower limb eccentric exercise in training leading to DOMS may experience increased pain and hypoesthesia which may predispose them to lower quarter joint trauma.

The relationship between stiffness and pain following unaccustomed eccentric exercise: the effects of gentle stretch and repeated bout.

To determine how muscle stiffness and pain which develop after eccentric exercise are affected by gentle stretching and repeated exercise. Twenty-one healthy female participants undertook eccentric exercise of the elbow flexors and changes in resting elbow flexion angle (REFA; a measure of muscle stiffness), pain on stretch scale, pain elicited by pressure (PPT pain, a measure of mechanoreceptor hypersensitivity), and upper arm girth were followed for 7 days after exercise. The effects of gentle passive stretching on pain and muscle stiffness were investigated 2 and 4 days after exercise. Eleven participants also repeated the exercise with the same arm 6 weeks after the first bout. There was a significant relationship between the pain on stretch scale and increased REFA (day 4; R2 = 0.65, p < 0.001), whereas there was no relationship between REFA and PPT pain. REFA was reduced by passive stretching and pain on stretch scale was also reduced from 3.0 (1.4, 5.1) to 0.75 (0.0, 2.0) [median (IQR), p = 0.01]. PPT pain was unaffected by the passive stretching, as was muscle swelling. Following the repeated bout, increases in REFA were much reduced, as was pain on stretch scale (p = 0.02). However, PPT pain was not significantly different between the two bouts of exercise. The results indicate that reductions in pain on stretch scale, either by gentle passive stretching or as the result of repeated exercise, are primarily due to reductions in muscle stiffness which develops after eccentric exercise, whereas mechanoreceptor hypersensitivity is relatively unaffected.

C-Reactive Protein Is Elevated Only in High Creatine Kinase Responders to Muscle Damaging Exercise.

The purpose of this study was to investigate if exertional rhabdomyolysis induced by an acute bout of plyometric exercise in untrained individuals was associated with histological characteristics of skeletal muscle, creatine kinase (CK) polymorphism or secondary damage. Twenty-six healthy male untrained individuals completed a bout of plyometric exercise (10 sets of 10 maximal squat jumps, with each standardized to achieve at least 95% of individual maximal jump height). Blood samples were taken, and perceived pain was scored immediately before the exercise intervention and 6 h, 1, 2, and 3 days post-intervention. Muscle biopsies were collected 9 or 4 days before (baseline) and 3 days after plyometric jumps. Subjects were divided into two groups, high (n = 10) and low responders (n = 16), based on a cut-off limit for exertional rhabdomyolysis of peak CK activity ≥ 1000 U/L in any post-exercise blood sample. Perceived pain was more severe assessed in squat than standing position. Low responders perceived more pain at 6 h and 1 day, while high responders perceived more pain than low responders on days three and four after exercise; structural (dystrophin staining) and ultra-structural (transmission electron microscopy) analysis of muscle fibers revealed no baseline pathology; damage was evident in all individuals in both groups, with no difference between high and low responders in either damage or fiber type proportion. High responders had significantly higher total white blood cell and neutrophil counts 6 h and significantly higher C-reactive protein (CRP) 6 h and days one and two after exercise compared to low responders. High responders had significantly greater muscle myeloperoxidase (MPO) levels in baseline and 3 day post-exercise biopsies compared to baseline of low responders. MLCK C49T single polymorphism was present in 26% of volunteers, whose CK responses were not higher than those with MLCK CC or CT genotype. In conclusion, perceived pain is more effectively assessed with potentially affected muscle under eccentric strain, even if static. High CK responders also have pronounced CRP responses to unaccustomed plyometric exercise intervention. Exertional rhabdomyolysis after unaccustomed eccentric exercise may be related to underlying inability to resolve intramuscular MPO.

Prolonged Low‐frequency Force Depression is Underestimated When Assessed with Doublets Compared to Trains

Unaccustomed eccentric exercise induces muscle damage, which leads to an impairment of force or torque that can last for several days. A common indirect measure of muscle damage is a greater depression of the force response to low‐frequency (e.g., 10Hz) compared to high‐frequency (e.g., 100Hz) stimulation; i.e., a post‐exercise reduction in the 10:100Hz ratio. This phenomenon is termed, prolonged low‐frequency force depression (PLFFD). Historically, trains of stimuli (e.g., 1s) have been used to evoke tetanic responses for the ratio. More recently, some authors have used only paired stimuli to evoke doublets. However, it is unknown if the PLFFD indicated by doublet responses is equivalent to the value derived from the traditional tetanic responses. Hence, the purpose of this study was to compare the magnitude of PLFFD determined by doublet vs. tetanic responses. We hypothesized that the doublet ratio (DR) would indicate significantly less PLFFD than the train ratio (TR). Eight participants (four females) performed 200 eccentric maximal voluntary contractions (4 sets of 50 repetitions, 1s rest between repetitions and 1 min rest between sets) of the dorsiflexors to induce muscle damage. Eccentric contractions were performed at 60°/s, started at a neutral ankle position, and finished at 30° of plantar flexion. Before the fatiguing protocol, baseline neuromuscular function was measured by a sequence of isometric contractions evoked by supramaximal electrical stimulation of the fibular nerve (paired stimuli at 10 and 100Hz, and 1s trains at 10 and 100Hz, each separated by 1s rest). This neuromuscular function test was repeated three times prior to fatigue and 2 min, 3 min, 5 min, 10 min and 48h after the fatiguing protocol. Using the peak torque of each response, 10:100Hz ratios were calculated at all time points; post‐exercise values were expressed as a percentage of the respective baseline ratio. At baseline, the DR was greater than TR (0.81 ± 0.04 vs. 0.48 ± 0.09; P &lt; 0.01). PLFFD was observed by 2 min for TR (73 ± 12%) and 3 min for DR (83 ± 9%), continued to develop over the acute recovery phase (at 10 min, DR = 73 ± 9%; TR = 51 ± 11%), and recovered by 48h (DR = 98 ± 6%; TR = 91 ± 12%). The TR was reduced more than the DR at all acute recovery time points (P &lt; 0.05), but not 48h. With DR and TR revealing different levels of PLFFD following damaging eccentric contractions, our results indicate that these techniques should not be used interchangeably. Whenever possible, trains of stimuli should be used to indicate the true extent of PLFFD. In cases where the reproducibility of the tetanic force response may be problematic (e.g., femoral nerve stimulation) or a train is deemed prohibitively uncomfortable, it should be acknowledged that paired stimuli will underestimate PLFFD.Support or Funding InformationSupported by NSERC, CFI and BCKDFThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The effect of L-Arginine supplementation on Delayed Onset Muscle Soreness (DOMS) after eccentric heavy exercise

Introduction: L-Arginine supplementation improves antioxidant defenses through L-Arginine/nitric oxide pathways. This investigation assesses the influences of acuteL-Arginine supplementation on selected markers of delayed onset muscle soreness (DOMS) after one by one heavy eccentric exercise in healthy young females. Methods: Twelve healthy young females students of the University of Mohaghegh-Ardabili voluntarily participated in a double-blind randomized-controlled crossover trial to estimate the effects of 3g L-Arginine oral supplementation versus placebo (3g glucose) following an unaccustomed heavy eccentric exercise. L-Arginine (ARG) or placebo (PLC) was taken immediately after squat exercise, separated by 10day washout. Measurements were conducted at baseline, 24, and 48h after exercise comprising: (a) TAC (b) CK (c) LDH (d) Visual Analogue Scale (VAS) (e) Range of Motion (ROM) of both knees (f) Edema of both thighs. For data analysis software SPSS version 20 was used. To analysis the data, analysis of variance with repeated measure was used. Results: TAC significantly increased 48h after exercise compared with the pre-exercise just in ARG group (P 0.05). Conclusion: The findings of this study suggest that acute supplementation of ARG after heavy eccentric exercise may alleviate muscle damage through promoting the antioxidant capacity, protein synthesis, or decrease of lactate accumulation.

Using DT-MRI and 31P-MRS to Assess Muscle Damage Following Unaccustomed Eccentric Exercise

PURPOSE: To detect the musculoskeletal structure and metabolism changes in vivo by diffusion tensor magnetic resonance imaging (DT-MRI) and 31P-Magnetic resonance spectroscopy (31P-MRS) after a single bout of eccentric exercise. METHODS: Thirty two male Sprague Dawley rats (body weight 238±15g) were randomly divided into either a sham group (n=8) or a downhill running group (n=24). Rats in the downhill running group ran 120 min on treadmill at a speed of 20 m/min at -16 degrees grade. DT-MRI and 31P-MRS were performed in right lower limb at pre-exercise (sham), immediately, 24 hr and 48 hr post-exercise at 7T MR. The MR sequence included RARE T2, RARE T1and EPI-DTI. MRS observational indices included the peak areas of inorganic phosphate concentration (Pi), phosphocreatine concentration (PCr) and the ratio of Pi/PCr. The morphological changes were confirmed by histological and immunohistochemical methods. One-way ANOVAs and Tukey’s test were used to assess the differences among different time points. RESULTS: On diffusion tensor tractography images, a single bout of downhill running significantly disrupted muscle fiber structure. The peak areas of Pi were significantly higher after exercise (pre-exercise: 4.1±0.8 mM; 0 hr post-exercise: 4.7±1.4 mM; 24 hr post-exercise: 6.6±1.9 mM; 48 hr post-exercise: 6.1±1.7 mM; all P<0.01). Muscle PCr did not differ between pre- and post-exercise; consequently, Pi/PCr values were significantly higher following EIMD (pre: 0.14±0.05; 0h post: 0.18±0.05; 24h post:0.22±0.08; 48h post: 0.2±0.08; all P<0.05). According to the histological detection, Z-band streaming was higher post-exercise compared with baseline (all P<0.05). The histopathological indices of damage coincided with changes in DT-MRI parameters of fractional anisotropy and apparent diffusion coefficient. CONCLUSIONS: The data suggest that exercise-induced muscle damage was accompanied by structural and metabolic alterations in skeletal muscle following a single bout of downhill running.The ability of DT-MRI and 31P-MRS to accurately detect these changes in vivo makes them promising approaches to evaluate skeletal muscle damage after unaccustomed exercise. (This research is supported by the National Natural Science Foundation of China, Grant#: 81301195)

Nociceptor interleukin 10 receptor 1 is critical for muscle analgesia induced by repeated bouts of eccentric exercise in the rat.

Delayed-onset muscle soreness is typically observed after strenuous or unaccustomed eccentric exercise. Soon after recovery, blunted muscle soreness is observed on repeated eccentric exercise, a phenomenon known as repeated bout effect (RBE). Although regular physical activity decreases muscle hyperalgesia, likely because of increased production of the anti-inflammatory cytokine interleukin-10 (IL-10) in the skeletal muscle, whether IL-10 also contributes to the antinociceptive effect of RBE is unknown. Furthermore, whether IL-10 attenuates muscle hyperalgesia by acting on muscle nociceptors remains to be established. Here, we explored the hypothesis that blunted muscle nociception observed in RBE depends on a local effect of IL-10, acting on IL-10 receptor 1 (IL-10R1) expressed by muscle nociceptors. Results show that after a second bout of eccentric exercise, rats exhibited decreased muscle hyperalgesia, indicative of RBE, and increased expression of IL-10 in the exercised gastrocnemius muscle. Although knockdown of IL-10R1 protein in nociceptors innervating the gastrocnemius muscle by intrathecal antisense oligodeoxynucleotide did not change nociceptive threshold in naive rats, it unveiled latent muscle hyperalgesia in rats submitted to eccentric exercise 12 days ago. Furthermore, antisense also prevented the reduction of muscle hyperalgesia observed after a second bout of eccentric exercise. These data indicate that recovery of nociceptive threshold after eccentric exercise and RBE-induced analgesia depend on a local effect of IL-10, acting on its canonical receptor in muscle nociceptors.

Intermittent hypobaric hypoxia combined with aerobic exercise improves muscle morphofunctional recovery after eccentric exercise to exhaustion in trained rats.

Unaccustomed eccentric exercise leads to muscle morphological and functional alterations, including microvasculature damage, the repair of which is modulated by hypoxia. We present the effects of intermittent hypobaric hypoxia and exercise on recovery from eccentric exercise-induced muscle damage (EEIMD). Soleus muscles from trained rats were excised before (CTRL) and 1, 3, 7, and 14 days after a double session of EEIMD protocol. A recovery treatment consisting of one of the following protocols was applied 1 day after the EEIMD: passive normobaric recovery (PNR), a 4-h daily exposure to passive hypobaric hypoxia at 4,000 m (PHR), or hypobaric hypoxia exposure followed by aerobic exercise (AHR). EEIMD produced an increase in the percentage of abnormal fibers compared with CTRL, and it affected the microvasculature by decreasing capillary density (CD, capillaries per mm2) and the capillary-to-fiber ratio (CF). After 14 days, AHR exhibited CD and CF values similar to those of CTRL animals (789 and 3.30 vs. 746 and 3.06) and significantly higher than PNR (575 and 2.62) and PHR (630 and 2.92). Furthermore, VEGF expression showed a significant 43% increase in AHR when compared with PNR. Moreover, after 14 days, the muscle fibers in AHR had a more oxidative phenotype than the other groups, with significantly smaller cross-sectional areas (AHR, 3,745; PNR, 4,502; and PHR, 4,790 µm2), higher citrate synthase activity (AHR, 14.8; PNR, 13.1; and PHR, 12 µmol·min-1·mg-1) and a significant 27% increment in PGC-1α levels compared with PNR. Our data show that hypoxia combined with exercise attenuates or reverses the morphofunctional alterations induced by EEIMD.NEW & NOTEWORTHY Our study provides new insights into the use of intermittent hypobaric hypoxia combined with exercise as a strategy to recover muscle damage induced by eccentric exercise. We analyzed the effects of hypobaric exposure combined with aerobic exercise on histopathological features of muscle damage, fiber morphofunctionality, capillarization, angiogenesis, and the oxidative capacity of damaged soleus muscle. Most of these parameters were improved after a 2-wk protocol of intermittent hypobaric hypoxia combined with aerobic exercise.

Whole Body Periodic Acceleration Improves Muscle Recovery after Eccentric Exercise.

The aim of this study was to determine whether whole body periodic acceleration (pGz) could improve muscle recovery after unaccustomed eccentric exercise (EE). Downhill treadmill running was used to elicit EE-induced muscle damage in mice, and pGz treatment (480 cycles per minute, 1 h·d) was applied daily for 10 d after the initial EE bout (day 0). Every 2 d during the pGz treatment course starting at day 0, we 1) assessed intracellular Ca and Na concentrations and membrane potential (as indicators of intracellular ion dysfunction) in vivo in gastrocnemius muscle from anesthetized animals and 2) quantified creatine kinase (CK), tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and interleukin-10 (IL-10) concentrations in plasma or muscle lysates (as indicators of muscle damage and inflammation). EE significantly increased intracellular Ca and Na, CK, TNF-α, MCP-1, IL-6, and IL-10, all of which peaked on day 2 with the exception of IL-10 and declined slowly over 10 d of recovery. pGz treatment after the EE bout mitigated ion dyshomeostasis and expedited recuperation to control values after 6 d of treatment. pGz treatment also accelerated the normalization of CK, TNF-α, MCP-1, and IL-6 while further increasing IL-10 concentrations. The nitric oxide synthase inhibitor L-N-nitroarginine methyl ester, administered in drinking water before and maintained throughout the treatment course, was sufficient to abrogate the salutary effects of pGz after EE. The present study demonstrates whole body periodic acceleration as an effective therapeutic strategy to accelerate muscle recovery after EE-induced skeletal muscle injury, as indicated by a faster normalization of all the studied parameters.

Protection from Muscle Damage in the Absence of Changes in Muscle Mechanical Behavior.

The repeated bout effect characterizes the protective adaptation after a single bout of unaccustomed eccentric exercise that induces muscle damage. Sarcomerogenesis and increased tendon compliance have been suggested as potential mechanisms for the repeated bout effect by preventing muscle fascicles from being stretched onto the descending limb of the length-tension curve (the region where sarcomere damage is thought to occur). In this study, evidence was sought for three possible mechanical changes that would support either the sarcomerogenesis or the increased tendon compliance hypotheses: a sustained rightward shift in the fascicle length-tension relationship, reduced fascicle strain amplitude, and reduced starting fascicle length. Subjects (n = 10) walked backward downhill (5 km·h, 20% incline) on a treadmill for 30 min on two occasions separated by 7 d. Kinematic data and medial gastrocnemius fascicle lengths (ultrasonography) were recorded at 10-min intervals to compare fascicle strains between bouts. Fascicle length-torque curves from supramaximal tibial nerve stimulation were constructed before, 2 h after, and 2 d after each exercise bout. Maximum torque decrement and elevated muscle soreness were present after the first, but not the second, backward downhill walking bout signifying a protective repeated bout effect. There was no sustained rightward shift in the length-torque relationship between exercise bouts, nor decreases in fascicle strain amplitude or shortening of the starting fascicle length. Protection from a repeated bout of eccentric exercise was conferred without changes in muscle fascicle strain behavior, indicating that sarcomerogenesis and increased tendon compliance were unlikely to be responsible. As fascicle strains are relatively small in humans, we suggest that changes to connective tissue structures, such as extracellular matrix remodeling, are better able to explain the repeated bout effect observed here.

Effects of Eccentric Exercise‐Induced Muscle Damage on Endothelial Function and Skeletal Muscle Microvascular Deoxygenation

Unaccustomed eccentric exercise has been shown to result in muscle damage (EIMD) and to decrease maximal aerobic exercise capacity (VO2max). Central and peripheral cardiovascular function mediates VO2 max, but it is unclear whether alterations in endothelial and skeletal muscle microvascular function play a role in the reduced VO2 max seen after EIMD. We tested the hypotheses that EIMD of the knee extensors would: 1) decrease local (femoral artery) and systemic (brachial artery) endothelial‐dependent flow‐mediated dilation (FMD), 2) alter the near‐infrared spectroscopy (NIRS)‐derived muscle microvascular deoxygenation (Δ[HHb]) response during incremental cycling exercise, which reflects the balance between muscle O2 delivery and O2 utilization, and 3) decrease VO2max. To date, five of a planned fifteen participants have completed a brachial and femoral artery FMD test, an index of endothelial‐dependent dilation, followed by an incremental exercise test to exhaustion on a cycle ergometer during which pulmonary VO2 and changes in NIRS‐derived Δ[HHb] were measured. Δ[HHb] was measured in the m. vastus lateralis, was normalized to the total response, and was then expressed as a function of relative work rate and fit using a sigmoid function. Each test was performed prior to (Pre) and 48‐hr after a bout of knee extensor eccentric exercise designed to elicit localized muscle damage (Post). Pre brachial artery FMD was 9.7 ± 8.9% and Post brachial artery FMD was 3.6 ± 7.3% (P = 0.1, Effect size (ES) = 0.3). Pre femoral artery FMD was 7.9 ± 7.4% compared to a Post FMD of 1.0 ± 4.4% (P = 0.1, ES = 1.1). During exercise the sigmoid slope was 35.4 ± 25.6 %/% Pre and 37.9 ± 22.1 %/% Post (P = 0.8, ES = .1) Similarly, the c/d value (i.e., 50% of the amplitude of the Δ[HHb] response was 46.7 ± 102.0 % Pre compared to 36.6 ± 46.7 % Post (P = 0.7, ES = 0.1). Pre VO2max was 3.3 ± 0.64 l·min−1 while Post VO2max was 3.1 ± 0.76 l·min−1 (P = 0.1, ES = 0.3). To date this study is under powered (0.08) and additional participants will be tested and included in the final analysis. The findings from this study will provide insight into macro‐ and microvascular function following EIMD and their association with changes in VO2max.

A semiquantitative scoring tool to evaluate eccentric exercise-induced muscle damage in trained rats.

Unaccustomed eccentric exercise is a well-documented cause of exercise-induced muscle damage. However, in trained subjects muscle injury involves only light or moderate tissue damage. Since trained rats are widely used as a model for skeletal muscle injury, here we propose a semiquantitative scoring tool to evaluate muscle damage in trained rats. Twenty male Sprague-Dawley rats were trained for two weeks following a two-week preconditioning period, and randomly divided into two groups: control rats (CTL; n=5) and rats with eccentric exercise-induced muscle damage (INJ; n=15). Injured rats were sacrificed at three time points: 1, 3 and 7 days post injury (n=5 each). Transverse sections from the right soleus were cut (10 µm) and stained with haematoxylin-eosin. Samples were evaluated by two groups of observers (four researchers experienced in skeletal muscle histopathology and four inexperienced) using the proposed tool, which consisted of six items organised in three domains: abnormal fibre morphology, necrotic/(re) degenerating fibres (muscle fibre domain), endomysial and perimysial infiltration (inflammatory state domain) and endomysium and perimysium distension (interstitial compartment domain). We observed the expected time course in the six evaluated items. Furthermore, agreement among observers was evaluated by measuring the Intraclass Correlation Coefficient (ICC). Within the experienced group, items from the muscle fibre and interstitial compartment domains showed good agreement and the two items from the infiltration compartment domain showed excellent agreement. In conclusion, the proposed tool allowed quick and correct evaluation of light to moderate muscle damage in trained rats with good agreement between observers.

Prophylactic Effects of Sauna on Delayed-Onset Muscle Soreness of the Wrist Extensors

Background:High-intensity of exercise or unaccustomed eccentric exercise can cause the phenomenon of Exercise-Induced Muscle Damage (EIMD) which usually results in cramps, muscle strain, impaired muscle function and delayed-onset muscle soreness.Objectives:This study investigated the prophylactic effects of sauna towards the symptoms associated with muscle damage from eccentric exercises of wrist extensor muscle group.Patients and Methods:A total of twenty-eight subjects (mean age 20.9 years old, SD = 1.6) were randomly divided into the sauna group (n = 14) and the control group (n = 14). In the sauna group, subjects received sauna before eccentric exercise of the wrist extensor. The eccentric exercises were conducted on the non-dominant arm by using an isokinetic dynamometer. Pain Intensity (PI), Pressure Pain Threshold (PPT) and passive range of motion of wrist flexion (PF-ROM) and extension (PE-ROM) were measured as pain variables. Grip Strength (GS) and Wrist Extension Strength (WES) were measured as variables of wrist extensor muscle function. All the measurements were performed at baseline, immediately after and from 1st to 8th days after the exercise-induced muscle damage.Results:The sauna group significantly demonstrated a lower deficit in ROM (passive flexion and passive extension), GS and WES following exercise than that of the control group (P < 0.05).Conclusions:Sauna application prior to the exercise-induced muscle damage demonstrated effectiveness in reduction of sensory impairment (PF-ROM and PE-ROM) and improvement of muscle functions (GS, and WES) in wrist extensor muscle group.

Enhanced Glycogen Storage of a Subcellular Hot Spot in Human Skeletal Muscle during Early Recovery from Eccentric Contractions.

Unaccustomed eccentric exercise is accompanied by muscle damage and impaired glucose uptake and glycogen synthesis during subsequent recovery. Recently, it was shown that the role and regulation of glycogen in skeletal muscle are dependent on its subcellular localization, and that glycogen synthesis, as described by the product of glycogen particle size and number, is dependent on the time course of recovery after exercise and carbohydrate availability. In the present study, we investigated the subcellular distribution of glycogen in fibers with high (type I) and low (type II) mitochondrial content during post-exercise recovery from eccentric contractions. Analysis was completed on five male subjects performing an exercise bout consisting of 15 x 10 maximal eccentric contractions. Carbohydrate-rich drinks were subsequently ingested throughout a 48 h recovery period and muscle biopsies for analysis included time points 3, 24 and 48 h post exercise from the exercising leg, whereas biopsies corresponding to prior to and at 48 h after the exercise bout were collected from the non-exercising, control leg. Quantitative imaging by transmission electron microscopy revealed an early (post 3 and 24 h) enhanced storage of intramyofibrillar glycogen (defined as glycogen particles located within the myofibrils) of type I fibers, which was associated with an increase in the number of particles. In contrast, late in recovery (post 48 h), intermyofibrillar, intramyofibrillar and subsarcolemmal glycogen in both type I and II fibers were lower in the exercise leg compared with the control leg, and this was associated with a smaller size of the glycogen particles. We conclude that in the carbohydrate-supplemented state, the effect of eccentric contractions on glycogen metabolism depends on the subcellular localization, muscle fiber’s oxidative capacity, and the time course of recovery. The early enhanced storage of intramyofibrillar glycogen after the eccentric contractions may entail important implications for muscle function and fatigue resistance.

Adaptation of local muscle blood flow and surface electromyography to repeated bouts of eccentric exercise.

The aim of this randomized controlled crossover study was to investigate the effect of a bout of unaccustomed eccentric exercise (ECC) followed by a consecutive bout of the same intensity on local muscle blood flow, amplitude, and frequency of the electromyographic (EMG) signal from the exercised tibialis anterior muscle. Sixteen healthy male participants (age, 25.7 (0.6) years; body mass index 24.8 (1) kg·m(-2) participated in this study. Two identical bouts of high-intensity ECC were performed on the tibialis anterior muscle 7 days apart. Control sessions involving no exercise were performed 4 weeks either before or after the exercise sessions. Changes in local total blood flow [ΔtHb], EMG root mean square, and median power frequency were recorded during isometric maximum voluntary contraction of ankle dorsiflexion. Measurements were performed before, immediately after, and the day after both ECCs (ECC1 and ECC2). The participants rested quietly in a chair in the control session. Eccentric exercise 1 led to a significant decrease in [ΔtHb] on the day after (p ≤ 0.05), whereas ECC2 did not. Median power frequency decreased significantly in ECC2 compared with ECC1 (p < 0.01). Root mean square was unchanged in all the instants. The present study showed that adaptation is depicted in the local muscle blood flow and the frequency contents of the EMG after an unaccustomed ECC inducing muscle soreness. These alterations provide a potential mechanism for a rapid adaptation, which decreases susceptibility of the muscle to develop further soreness in the subsequent ECC bout.

Preventive effects of 10-day supplementation with saffron and indomethacin on the delayed-onset muscle soreness.

Delayed-onset muscle soreness (DOMS) often occurs after unaccustomed eccentric exercise and reduces exercise performance. We aimed to study the preventive effects of saffron and indomethacin on the biochemical and functional indicators of DOMS after 1-session eccentric exercise. A 10-day, randomized, double-blind, placebo-controlled, pretest-posttest design. Controlled research laboratory. Thirty-nine nonactive male university students randomly divided into saffron (n = 12), indomethacin (n = 12), and control (n = 15) groups. Saffron group received 1 capsule containing dried saffron powder (n = 12, 300 mg/d), indomethacin group received 75 mg indomethacin (n = 12, 25 mg thrice a day), and control group (n = 15) received placebo capsules, 1 week before and 3 days after eccentric exercise. Ten days before and 24, 48, and 72 hours after muscle soreness protocol, the maximum isometric and isotonic forces, plasma creatine kinase (CK), plasma lactate dehydrogenase (LDH), perceived pain, knee range of movement, and thigh circumference were measured. Muscle soreness protocol was performed with a weight load equal to 80% of the maximum isotonic force in 4 sessions with 20 repetitions and 3-minute rest in between. This study shows that 10-day supplementation with 300 mg saffron significantly decreased the CK and LDH concentrations (P < 0.0001). In the saffron group, there was no decline in maximum isometric and isotonic forces after eccentric exercise, but a significant decline in the isometric force was observed in the control group (P < 0.0001). No pain was reported in the saffron group, whereas the indomethacin group experienced pain before 72 hours (P < 0.001). Results obtained from the current novel research indicate a strong preventive effect of 10-day supplementation with saffron on the DOMS. The saffron can be used to prevent DOMS and alleviate the DOMS symptoms.

Alterations in Whole-Body Insulin Sensitivity Resulting From Repeated Eccentric Exercise of a Single Muscle Group: A Pilot Investigation.

Unaccustomed eccentric exercise using large muscle groups elicits soreness, decrements in physical function and impairs markers of whole-body insulin sensitivity; although these effects are attenuated with a repeated exposure. Eccentric exercise of a small muscle group (elbow flexors) displays similar soreness and damage profiles in response to repeated exposure. However, it is unknown whether damage to small muscle groups impacts upon whole-body insulin sensitivity. This pilot investigation aimed to characterize whole-body insulin sensitivity in response to repeated bouts of eccentric exercise of the elbow flexors. Nine healthy males completed two bouts of eccentric exercise separated by 2 weeks. Insulin resistance (updated homeostasis model of insulin resistance, HOMA2-IR) and muscle damage profiles (soreness and physical function) were assessed before, and 48 h after exercise. Matsuda insulin sensitivity indices (ISI Matsuda) were also determined in 6 participants at the same time points as HOMA2-IR. Soreness was elevated, and physical function impaired, by both bouts of exercise (both p < .05) but to a lesser extent following bout 2 (time x bout interaction, p < .05). Eccentric exercise decreased ISI Matsuda after the first but not the second bout of eccentric exercise (time x bout interaction p < .05). Eccentric exercise performed with an isolated upper limb impairs whole-body insulin sensitivity after the first, but not the second, bout.