Muscle damage and inflammation during recovery from exercise

Hepcidin and iron: novel findings for elite female rugby Sevens players

BACKGROUND

Iron deficiency is a common deficiency disease worldwide with athletes at increased risk.

METHODS

A proposed new mechanism of exercise-induced iron deficiency in athletes involves the iron-regulatory hormone hepcidin, however, there is limited information on this amongst elite athletes. This study describes iron status in elite female rugby Sevens players.

RESULTS

Blood samples were collected at the start and mid-season and analyzed for serum iron, serum ferritin (SF), soluble transferring receptor (sTfR), high sensitivity C-reactive Protein (hsCRP) and hepcidin. Of the 17 players 18% were iron deficient (SF<30 µg/L) with 29-35% of players with sub-optimal iron stores at some point during the study (SF<45 µg/L). Serum hepcidin was strongly correlated with SF (r=0.61, P=0.0001).

CONCLUSIONS

Some elite female rugby Sevens players have sub-optimal iron stores over the course of a season.

The impact of skeletal muscle contraction on CD146+Lin- pericytes

Unaccustomed resistance exercise can initiate skeletal muscle remodeling and adaptive mechanisms that can confer protection from damage and enhanced strength with subsequent stimulation. The myofiber may provide the primary origin for adaptation, yet multiple mononuclear cell types within the surrounding connective tissue may also contribute. The purpose of this study was to evaluate the acute response of muscle-resident interstitial cells to contraction initiated by electrical stimulation (e-stim) and subsequently determine the contribution of pericytes to remodeling as a result of training. Mice were subjected to bilateral e-stim or sham treatment. Following a single session of e-stim, NG2+CD45-CD31- (NG2+Lin-) pericyte, CD146+Lin- pericyte, and PDGFRα+ fibroadipogenic progenitor cell quantity and function were evaluated via multiplex flow cytometry and targeted quantitative PCR. Relative quantity was not significantly altered 24 h postcontraction, yet unique gene signatures were observed for each cell population at 3 h postcontraction. CD146+Lin- pericytes appeared to be most responsive to contraction, and upregulation of genes related to immunomodulation and extracellular matrix remodeling was observed via RNA sequencing. Intramuscular injection of CD146+Lin- pericytes did not significantly increase myofiber size yet enhanced ECM remodeling and angiogenesis in response to repeated bouts of e-stim for 4 wk. The results from this study provide the first evidence that CD146+Lin- pericytes are responsive to skeletal muscle contraction and may contribute to the beneficial outcomes associated with exercise.

Mineralocorticoid Receptor Signaling Contributes to Normal Muscle Repair After Acute Injury

Acute skeletal muscle injury is followed by a temporal response of immune cells, fibroblasts, and muscle progenitor cells within the muscle microenvironment to restore function. These same cell types are repeatedly activated in muscular dystrophy from chronic muscle injury, but eventually, the regenerative portion of the cycle is disrupted and fibrosis replaces degenerated muscle fibers. Mineralocorticoid receptor (MR) antagonist drugs have been demonstrated to increase skeletal muscle function, decrease fibrosis, and directly improve membrane integrity in muscular dystrophy mice, and therefore are being tested clinically. Conditional knockout of MR from muscle fibers in muscular dystrophy mice also improves skeletal muscle function and decreases fibrosis. The mechanism of efficacy likely results from blocking MR signaling by its endogenous agonist aldosterone, being produced at high local levels in regions of muscle damage by infiltrating myeloid cells. Since chronic and acute injuries share the same cellular processes to regenerate muscle, and MR antagonists are clinically used for a wide variety of conditions, it is crucial to define the role of MR signaling in normal muscle repair after injury. In this study, we performed acute injuries using barium chloride injections into tibialis anterior muscles both in myofiber MR conditional knockout mice on a wild-type background (MRcko) and in MR antagonist-treated wild-type mice. Steps of the muscle regeneration response were analyzed at 1, 4, 7, or 14 days after injury. Presence of the aldosterone synthase enzyme was also assessed during the injury repair process. We show for the first time aldosterone synthase localization in infiltrating immune cells of normal skeletal muscle after acute injury. MRcko mice had an increased muscle area infiltrated by aldosterone synthase positive myeloid cells compared to control injured animals. Both MRcko and MR antagonist treatment stabilized damaged myofibers and increased collagen infiltration or compaction at 4 days post-injury. MR antagonist treatment also led to reduced myofiber size at 7 and 14 days post-injury. These data support that MR signaling contributes to the normal muscle repair process following acute injury. MR antagonist treatment delays muscle fiber growth, so temporary discontinuation of these drugs after a severe muscle injury could be considered.

Angiotensin-Converting Enzyme Related-Polymorphisms on Inflammation, Muscle and Myocardial Damage After a Marathon Race

Muscle damage is one of the most important factors that affect muscle fatigue during endurance exercise. Recent evidence suggests that the renin–angiotensin system impacts on skeletal muscle wasting. The aim of this study was to determine association between the AGT Met235Thr, ACE I/D and BDKRB2 −9/+9 polymorphisms with inflammation, myocardial and muscle injury induced by endurance exercise. Eighty-one Brazilian male runners participated in this study and completed the International Marathon of Sao Paulo. Muscle and myocardial damage markers (alanine transaminase, ALT, aspartate transaminase, AST, lactic dehydrogenase, LDH, creatine kinase, CK, Troponin, pro BNP, myoglobin, and CK-MB) and inflammatory mediators (IL-6, IL-8, IL-10, IL12p70, IL1β, and TNF-α) were determined one day before, immediately after, one day after, and three days after the event. Muscle damage was also determined fifteen days after race and angiotensinogen (AGT) Met235Thr, angiotensin-converting enzyme (ACE) I/D, and Bradykinin B2 receptor (BDKRB2) −9/+9 polymorphisms were determined. Marathon race participation induced an increase in all muscle damage and inflammatory markers evaluated (p < 0.0001). The muscle damage markers, troponin and pro BNP, CK and LDH and inflammatory markers, IL-6, IL-8, IL-1β and IL-10 were also higher in ACE II genotype immediately after race, compared to DD genotype. The percentage of runners higher responders (>500U/I) to CK levels was higher for II genotypes (69%) compared to DD and ID genotypes (38% and 40%, respectively) immediately after. Troponin, pro BNP and IL-1β, IL-8 levels were also elevated in AGT MM genotype compared to TT genotype athletes after and/or one day after race. BDKRB2 −9/−9 had pronounced response to LDH, CK, CK-MB and ALT and AST activities, myoglobin, troponin, IL-6, IL-8 levels immediately, one day and/or three days after race. The percentage of runners higher responders (>500U/I) to CK levels was greater for −9−9 and −9+9 genotypes (46 and 48%, respectively) compared to +9+9 genotypes (31%) immediately after. ACE II, AGT MM, and BDKRB2 −9−9 genotypes may increase the susceptibility to inflammation, muscle injury after endurance exercise and could be used to predict the development of clinical conditions associated with muscle damage and myocardial injury.

Post-Exercise Recovery Following 30-Day Supplementation of Trans-Resveratrol and Polyphenol-Enriched Extracts

Background: The purpose of this study was to investigate the effects of 30-day consumption of trans-resveratrol and polyphenol-enriched extracts on indices of exercise-induced muscle damage (EIMD) and performance following eccentric-loaded resistance exercise (ECRE). Methods: Following 30 days of resveratrol-polyphenol (RES) (n = 10) or placebo control (CTL) (n = 12) supplementation, subjects performed a bout of ECRE to induce EIMD. EIMD biomarkers, perceived soreness, pain threshold and tolerance, range of motion, and performance were measured before and 24 and 48 h after ECRE. Results: CTL subjects demonstrated increased soreness at 24 (p = 0.02) and 48 h (p = 0.03) post-ECRE, while RES subjects reported increased soreness at 24 h post-ECRE (p = 0.0003). CTL subjects exhibited decreased pain threshold in the vastus lateralis at 24 h post-ECRE (p = 0.03). CTL subjects also displayed decreased pain tolerance in the vastus intermedius at 24 h post-ECRE (p = 0.03) and the vastus lateralis at 24 (p = 0.003) and 48 h (p = 0.003). RES participants showed no change in pain threshold or tolerance from baseline. CTL subjects showed a decrease in mean (p = 0.04) and peak power (p = 0.04) at 24 h post-ECRE, while RES participants demonstrated no changes from baseline. No between-group differences were observed for the changes in serum creatine kinase. Serum C-reactive protein increased similarly in both groups at 24 h post-ECRE (p < 0.002), remaining elevated in CTL subjects while RES participants demonstrated a decline from 24 to 48 h (p = 0.04). Serum interleukin 6 increased at 24 h post-ECRE in both groups (p < 0.003) followed by a decrease from 24 to 48 h, returning to baseline levels only for RES subjects. Conclusion: Trans-resveratrol and polyphenol-enriched extract supplementation may support the attenuation of soreness and inflammation and improve performance recovery following ECRE without modulation of indirect biomarkers of EIMD.

Association of Daily Dietary Intake and Inflammation Induced by Marathon Race

Daily food intake is crucial to maintain health and determine endogenous fuel to practice endurance exercise. We investigated the association between quantity of macronutrient and micronutrient daily intake and inflammation induced by long-distance exercise. Methods. Forty-four Brazilian male amateurs' marathon finishers from 30 to 55 years old participated in this study. Blood samples were collected 1 day before, immediately after, and 1 day and 3 days after São Paulo International Marathon. The serum levels of IL-6, IL-1β, IL-10, IL-8, IL-12p70, and TNF-α were measured to evaluate inflammation. Dietary intake was determined using a prospective method of three food records in the week before marathon race. Results. Marathon race promoted an elevation on IL-6, IL-8, IL-1-β, and IL-10 immediately after the race. The energy intake (EI), carbohydrate, fiber, folic acid, vitamin E, vitamin D, calcium, magnesium, and potassium intakes was below recommended. Immediately after the marathon race, we observed a negative correlation between IL-8 and daily EI, carbohydrate, fiber, fat, iron, calcium, potassium, and sodium intakes, and higher levels of IL-8 on runners with <3 g/kg/day of carbohydrate intake compared to runners with >5 g/kg/day. We demonstrated a positive correlation between daily carbohydrate intake and IL-10 and a negative correlation between TNF-α and % of energy intake recommended, carbohydrate and fiber intakes. Finally, runners with adequate EI had lower levels of IL-1β and TNF-α compared with low EI immediately after the race. Conclusion. Nutrition strategies to promote balanced diet in amateur runners seem to be as important as immunonutrition sports market. Daily food intake, mainly EI, electrolyte and carbohydrate intakes, may modulate exacerbated inflammation after endurance exercise.

Artificial intelligence identified peptides modulate inflammation in healthy adults

Dietary bioactive peptides have been, among many functionalities, associated with immune modulation and thereby may improve resolution of inflammation. The goals of this research were to assess (1) whether specific peptides with immune-modulating activity consumed as part of a rice protein hydrolysate could be absorbed into blood and (2) whether they modulate inflammation markers. Artificial intelligence algorithms were applied to target, predict and unlock inflammation-modulating peptides from rice protein. A food application was developed containing four bioactive peptides. Protein docking simulation studies revealed high binding energies of these peptides with inflammation markers. In a small kinetic study 10 healthy subjects consumed the peptides with a single bolus of 20 g protein hydrolysate. Although absorption of the four predicted peptides at plasma concentrations deemed biologically relevant could not be confirmed (quantitative LC-MS/MS), several cytokines responded (ELISA kits). The 24-hour kinetic study revealed a slight suppression of pro-inflammatory TNF-α, IP-10 and NOx, whereas IL-6 increased temporarily (timepoints 2-12 hours). These markers returned to the baseline after 24 hours whereas others were not affected significantly (IL-10, hs-CRP, IL-8, and MCP-1). Consumption of a single dose protein hydrolysate containing immune modulatory peptides induced a mild temporary response most likely through intestinal signaling. Forthcoming studies will examine dietary supplementation in situations of stress.

The Temporal Relationship Between Exercise, Recovery Processes, and Changes in Performance

Physiological and psychological demands during training and competition generate fatigue and reduce an athlete’s sport-specific performance capacity. The magnitude of this decrement depends on several characteristics of the exercise stimulus (eg, type, duration, and intensity), as well as on individual characteristics (eg, fitness, profile, and fatigue resistance). As such, the time required to fully recover is proportional to the level of fatigue, and the consequences of exercise-induced fatigue are manifold. Whatever the purpose of the ensuing exercise session (ie, training or competition), it is crucial to understand the importance of optimizing the period between exercise bouts in order to speed up the regenerative processes and facilitate recovery or set the next stimulus at the optimal time point. This implies having a fairly precise understanding of the fatigue mechanisms that contribute to the performance decrement. Failing to respect an athlete’s recovery needs may lead to an excessive accumulation of fatigue and potentially “nonfunctional overreaching” or to maladaptive training. Although research in this area recently increased, considerations regarding the specific time frames for different physiological mechanisms in relation to exercise-induced fatigue are still missing. Furthermore, recommendations on the timing and dosing of recovery based on these time frames are limited. Therefore, the aim of this article is to describe time courses of recovery in relation to the exercise type and on different physiological levels. This summary supports coaches, athletes, and scientists in their decision-making process by considering the relationship of exercise type, physiology, and recovery.

Comparative efficacy of active recovery and cold water immersion as post-match recovery interventions in elite youth soccer

The current study compared cold-water immersion (CWI) and active recovery (AR) to static stretching (SS) on muscle recovery post-competitive soccer matches in elite youth players (n = 15). In a controlled crossover design, participants played a total of nine competitive soccer games, comprising three 80 minute games for each intervention (SS, CWI and AR). Muscle oedema, creatine kinase (CK), countermovement jump performance (CMJA) and perceived muscle soreness (PMS) were assessed pre-, immediately post-, and 48 hours post-match and compared across time-intervals and between interventions. Following SS, all markers of muscle damage remained significantly elevated (P < 0.05) compared to baseline at 48 hours post-match. Following AR and CWI, CMJA returned to baseline at 48 hours post-match, whilst CK returned to baseline following CWI at 48 hours post-match only. Analysis between recovery interventions revealed a significant improvement in PMS (P < 0.05) at 48 hours post-match when comparing AR and CWI to SS, with no significant differences between AR and CWI observed (P > 0.05). Analysis of %change for CK and CMJA revealed significant improvements for AR and CWI compared to SS. The present study indicated both AR and CWI are beneficial recovery interventions for elite young soccer players following competitive soccer matches, of which were superior to SS.

Effects of dietary nitrate on inflammation and immune function, and implications for cardiovascular health

Inorganic dietary nitrate, found abundantly in green leafy and some root vegetables, elicits several beneficial physiological effects, including a reduction in blood pressure and improvements in blood flow through nitrate-nitrite-nitric oxide signaling. Recent animal and human studies have shown that dietary nitrate and nitrite also modulate inflammatory processes and immune cell function and phenotypes. Chronic low-grade inflammation and immune dysfunction play a critical role in cardiovascular disease. This review outlines the current evidence on the efficacy of nitrate-rich plant foods and other sources of dietary nitrate and nitrite to counteract inflammation and promote homeostasis of the immune and vascular systems. The data from these studies suggest that immune cells and immune-vasculature interactions are important targets for dietary interventions aimed at improving, preserving, or restoring cardiovascular health.

Shoulder Lameness in Dogs: Preliminary Investigation on Ultrasonography, Signalment and Hemato-Biochemical Findings Correlation

Forelimb lameness in medium and large breed dogs is frequently caused by traumatic or degenerative injuries of the shoulder. Patient history, physical examination, x-rays, blood, and chemical work are routinely used to achieve diagnosis, and may be associated with ultrasonography or magnetic resonance imaging. Ultrasonography is increasingly popular in small animal practice due to its low cost, ease of repetition, and the fact that it is non-invasive and can be performed in conscious patients. It is also widely accepted that muscular stress or injuries can induce detectable variations in blood and chemical work. The aim of this preliminary study is to search for correlation between measurements of selected hematobiochemical parameters and ultrasound diagnosis in dogs affected by shoulder injuries. A retrospective study was conducted on orthopedic clinical records of dogs presented to our Veterinary Teaching Hospital for lameness caused by shoulder problems over a period of 5 years. Dogs with both hematobiochemical and ultrasound examinations were selected. Patients were classified into 5 groups according to ultrasound diagnosis: (1) mild/moderate tendinopathy, (2) severe tendinopathy, (3) articular damage, (4) chronic myopathy, and (5) neoplastic injury. Statistical analysis was performed to detect possible correlations between group and hematobiochemical parameters. Forty-four dogs met the inclusion criteria and forty-nine shoulders were diagnosed as injured. Significant differences were found between the age, sex, body weight, neutrophil count, and AST levels. In particular, statistically significant increases were found for neutrophil count and AST concentration in case of ultrasonographically diagnosed severe tendinopathy, articular damage, and neoplastic pathology. Further and wider studies are suggested to determine whether these biomarkers can become a useful diagnostic aid.

Acid sphingomyelinase inhibition alleviates muscle damage in gastrocnemius after acute strenuous exercise

[Purpose]

Strenuous exercise often induces skeletal muscle damage, which results in impaired performance. Sphingolipid metabolism contributes to various cellular processes, including apoptosis, stress response, and inflammation. However, the relationship between exercise-induced muscle damage and ceramide (a key component of sphingolipid metabolism), is rarely studied. The present study aimed to explore the regulatory role of sphingolipid metabolism in exercise-induced muscle damage.

[Methods]

Mice were subjected to strenuous exercise by treadmill running with gradual increase in intensity. The blood and gastrocnemius muscles (white and red portion) were collected immediately after and 24 h post exercise. For 3 days, imipramine was intraperitoneally injected 1 h prior to treadmill running.

[Results]

Interleukin 6 (IL-6) and serum creatine kinase (CK) levels were enhanced immediately after and 24 h post exercise (relative to those of resting), respectively. Acidic sphingomyelinase (A-SMase) protein expression in gastrocnemius muscles was significantly augmented by exercise, unlike, serine palmitoyltransferase-1 (SPT-1) and neutral sphingomyelinase (N-SMase) expressions. Furthermore, imipramine (a selective A-SMase inhibitor) treatment reduced the exercise-induced CK and IL-6 elevations, along with a decrease in cleaved caspase-3 (Cas-3) of gastrocnemius muscles.

[Conclusion]

We found the crucial role of A-SMase in exercise-induced muscle damage.

Effect of Cocoa Products and Its Polyphenolic Constituents on Exercise Performance and Exercise-Induced Muscle Damage and Inflammation: A Review of Clinical Trials

In recent years, the consumption of chocolate and, in particular, dark chocolate has been "rehabilitated" due to its high content of cocoa antioxidant polyphenols. Although it is recognized that regular exercise improves energy metabolism and muscle performance, excessive or unaccustomed exercise may induce cell damage and impair muscle function by triggering oxidative stress and tissue inflammation. The aim of this review was to revise the available data from literature on the effects of cocoa polyphenols on exercise-associated tissue damage and impairment of exercise performance. To this aim, PubMed and Web of Science databases were searched with the following keywords: "intervention studies", "cocoa polyphenols", "exercise training", "inflammation", "oxidative stress", and "exercise performance". We selected thirteen randomized clinical trials on cocoa ingestion that involved a total of 200 well-trained athletes. The retrieved data indicate that acute, sub-chronic, and chronic cocoa polyphenol intake may reduce exercise-induced oxidative stress but not inflammation, while mixed results are observed in terms of exercise performance and recovery. The interpretation of available results on the anti-oxidative and anti-inflammatory activities of cocoa polyphenols remains questionable, likely due to the variety of physiological networks involved. Further experimental studies are mandatory to clarify the role of cocoa polyphenol supplementation in exercise-mediated inflammation.

Biomarkers in Inflammatory Myopathies-An Expanded Definition

Biomarkers as parameters of pathophysiological conditions can be of outmost relevance for inflammatory myopathies. They are particularly warranted to inform about diagnostic, prognostic, and therapeutic questions. As biomarkers become more and more relevant in daily routine, this review focusses on relevant aspects particularly addressing myopathological features. However, the level of evidence to use them in daily routine at presence is low, still since none of them has been validated in large cohorts of patients and rarely in independent biopsy series. Hence, they should be read as mere expert opinions. The evaluation of biomarkers as well as key biological parameters is an ongoing process, and we start learning about relevance of them, as we must recognize that pathophysiology of myositis is biologically incompletely understood. As such this approach should be considered an essay toward expansion of the definition “biomarker” to myositis, an emerging field of interest in biomedical research.

CXCL10 increases in human skeletal muscle following damage but is not necessary for muscle regeneration

CXCL10 is a chemokine for activated and memory T cells with many important immunological functions. We recently found that CXCL10 is upregulated in human muscle following contraction‐induced damage. No information is available on the role of CXCL10 in the context of muscle damage or repair. In this study, we confirm that CXCL10 is elevated in human muscle at 2 and 3 days following damage and perform cell culture and animal studies to examine the role of CXCL10 in muscle repair. CXCL10 did not impact proliferation rates of human primary myoblasts but it did promote myogenic differentiation in vitro, suggesting a possible direct impact on muscle regeneration. To test if CXCL10 was dispensable for effective muscle regeneration in vivo, we measured functional and histological markers of muscle repair out to 14 days postmuscle injury caused by a myotoxin in wild‐type (WT) mice and CXCL10 knockout (KO) mice. Between genotypes, no significant differences were found in loss or restoration of in situ muscle force, cross‐sectional area of newly formed myofibers, or the number of embryonic myosin heavy chain‐positive myofibers. In addition, KO animals were not deficient in T‐cell accumulation in the damaged muscle following injury. Gene expression of the other two ligands (CXCL9 and 11) that bind to the same receptor as CXCL10 were also elevated in the damaged muscle of KO mice. Thus, other ligands may have compensated for the lack of CXCL10 in the KO mice. We conclude that CXCL10 is not necessary for effective muscle regeneration.

Muscle oxygenation induced by cycling exercise does not accelerate recovery kinetics following exercise-induced muscle damage in humans: A randomized cross-over study

The aim of this study was to analyze the effects of inducing muscle oxygenation using an intermittent cycling exercise on recovery kinetics after exercise-induced muscle damage. Ten soccer players performed single-leg knee flexors exercise: 75 eccentric contractions. The day after, subjects performed an intermittent cycling exercise of 12 min (15 s work - 15 s rest) or recovered passively in a balanced and randomized cross-over design. Force, single and double-leg countermovement jumps, muscle soreness, perceived recovery and creatine kinase concentrations were assessed through a 72 h period. Oxygenation during cycling was assessed using Near Infrared Spectroscopy. Results showed an increase in knee flexors oxygenation using intermittent cycling (ΔHbO₂ = 70.2 ± 19.8% ; ΔHHb = 68.2 ± 14.1%). Possibly small detrimental effect of cycling on eccentric force was found (ES = -0.58, 90% CI: -1.33 to 0.17). Small detrimental effects of cycling were found for soreness and perceived recovery. Implementing intermittent cycling exercise the day after muscle damage may be detrimental for recovery.

Muscle and Systemic Molecular Responses to a Single Flywheel Based Iso-Inertial Training Session in Resistance-Trained Men

Growing evidence points to the effectiveness of flywheel (FW) based iso-inertial resistance training in improving physical performance capacities. However, molecular adaptations induced by FW exercises are largely unknown. Eight resistance-trained men performed 5 sets of 10 maximal squats on a FW device. Muscle biopsies (fine needle aspiration technique) and blood samples were collected before (t0), and 2 h (t1) after FW exercise. Blood samples were additionally drawn after 24 h (t2) and 48 h (t3). Paired samples t-tests revealed significant increases, at t1, of mRNA expression of the genes involved in inflammation, in both muscle (MCP-1, TNF-α, IL-6) and peripheral blood mononuclear cells (IkB-α, MCP-1). Circulating extracellular vesicles (EVs) and EV-encapsulated miRNA levels (miR-206, miR-146a) significantly increased at t1 as well. Conversely, muscle mRNA level of genes associated with muscle growth/remodeling (IGF-1Ea, cyclin D1, myogenin) decreased at t1. One-way repeated measure ANOVAs, with Bonferroni corrected post-hoc pairwise comparisons, revealed significant increases in plasma concentrations of IL-6 (t1; t2; t3) and muscle creatine kinase (t1; t2), while IGF-1 significantly increased at t2 only. Our findings show that, even in experienced resistance trained individuals, a single FW training session modifies local and systemic markers involved in late structural remodeling and functional adaptation of skeletal muscle.

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.

The compelling link between physical activity and the body's defense system

This review summarizes research discoveries within 4 areas of exercise immunology that have received the most attention from investigators: (1) acute and chronic effects of exercise on the immune system, (2) clinical benefits of the exercise-immune relationship, (3) nutritional influences on the immune response to exercise, and (4) the effect of exercise on immunosenescence. These scientific discoveries can be organized into distinctive time periods: 1900-1979, which focused on exercise-induced changes in basic immune cell counts and function; 1980-1989, during which seminal papers were published with evidence that heavy exertion was associated with transient immune dysfunction, elevated inflammatory biomarkers, and increased risk of upper respiratory tract infections; 1990-2009, when additional focus areas were added to the field of exercise immunology including the interactive effect of nutrition, effects on the aging immune system, and inflammatory cytokines; and 2010 to the present, when technological advances in mass spectrometry allowed system biology approaches (i.e., metabolomics, proteomics, lipidomics, and microbiome characterization) to be applied to exercise immunology studies. The future of exercise immunology will take advantage of these technologies to provide new insights on the interactions between exercise, nutrition, and immune function, with application down to the personalized level. Additionally, these methodologies will improve mechanistic understanding of how exercise-induced immune perturbations reduce the risk of common chronic diseases.

Prolonged low-frequency force depression is underestimated when assessed with doublets compared with tetani in the dorsiflexors

Prolonged low-frequency force depression (PLFFD) after damaging eccentric exercise may last for several days. Historically, PLFFD has been calculated from the tetanic force responses to trains of supramaximal stimuli. More recently, for methodological reasons, stimulation has been reduced to two pulses. However, it is unknown whether doublet responses provide a valid measure of PLFFD in the days after eccentric exercise. In 12 participants, doublets and tetani were elicited at 10 and 100 Hz before and after (2, 3, 5 min, 48 and 96 h) 200 eccentric maximal voluntary contractions of the dorsiflexors. Doublet and tetanic torque responses at 10 Hz were similarly depressed throughout recovery (P > 0.05; e.g., 2 min: 58.9 ± 12.8% vs. 57.1 ± 14.5% baseline; 96 h: 85.6 ± 11.04% vs. 85.1 ± 10.8% baseline). At 100 Hz, doublet torque was impaired more than tetanic torque at all time points (P < 0.05; e.g., 2 min: 70.5 ± 14.2% vs. 88.1 ± 11.7% baseline; 96 h: 83.0 ± 14.2% vs. 98.7 ± 9.5% baseline). As a result, the postfatigue reduction of the 10 Hz-to-100 Hz ratio (PLFFD) was markedly greater for tetani than for doublets (P < 0.05; e.g., 2 min: 64.3 ± 15.1% vs. 83.0 ± 5.8% baseline). In addition, the doublet ratio recovered by 48 h (99.2 ± 5.0% baseline), whereas the tetanic ratio was still impaired at 96 h (88.2 ± 9.7% baseline). Our results indicate that doublets are not a valid measure of PLFFD in the minutes and days after eccentric exercise. If study design favors the use of paired stimuli, it should be acknowledged that the true magnitude and duration of PLFFD are likely underestimated. NEW & NOTEWORTHY Prolonged low-frequency force depression (PLFFD) will result from damaging exercise and may last for several days. After 200 eccentric maximal dorsiflexor contractions, we compared the gold-standard measure of PLFFD (calculated using trains of supramaximal stimulation) to the value obtained from an alternative technique that is becoming increasingly common (paired supramaximal stimuli). Doublets underestimated the magnitude and duration of PLFFD compared with tetani, so caution must be used when reporting PLFFD derived from paired stimuli.

Assessing the usefulness of acute physiological responses following resistance exercise: sensitivity, magnitude of change, and time course of measures

A variety of strategies exist to modulate the acute physiological responses following resistance exercise aimed at enhancing recovery and/or adaptation processes. To assess the true impact of these strategies, it is important to know the ability of different measures to detect meaningful change. We investigated the sensitivity of measures used to quantify acute physiological responses to resistance exercise and constructed a physiological profile to characterise the magnitude of change and the time course of these responses. Eight males accustomed to regular resistance exercise performed experimental sessions during a “control week”, void of an exercise stimulus. The following week, termed the “exercise week”, participants repeated this sequence of experimental sessions, and they also performed a bout of lower-limb resistance exercise following the baseline assessments. Assessments were conducted at baseline and at 2, 6, 24, 48, 72, and 96 h after the intervention. On the basis of the signal-to-noise ratio, the most sensitive measures were maximal voluntary isometric contraction, 20-m sprint, countermovement jump peak force, rate of force development (100–200 ms), muscle soreness, Daily Analysis Of Life Demands For Athletes part B, limb girth, matrix metalloproteinase-9, interleukin-6, creatine kinase, and high-sensitivity C-reactive protein with ratios >1.5. Clear changes in these measures following resistance exercise were determined via magnitude-based inferences. These findings highlight measures that can detect real changes in acute physiological responses following resistance exercise in trained individuals. Researchers investigating strategies to manipulate acute physiological responses for recovery and/or adaptation can use these measures, as well as the recommended sampling points, to be confident that their interventions are making a worthwhile impact.

Exercise-Induced Illness and Inflammation: Can Immunonutrition and Iron Help?

The main focus of this review is illness among elite athletes, how and why it occurs, and whether any measures can be taken to combat it or to prevent its onset. In particular, there is particular interest in exercise-induced immunodepression, which is a result of the immune system regarding exercise (e.g., prolonged, exhaustive exercise) as a challenge to its function. This promotes the inflammatory response. There is often a high incidence of illness in athletes after undertaking strenuous exercise, particularly among those competing in endurance events, not only mainly in terms of upper respiratory tract illness, but also involving gastrointestinal problems. It may well be that this high incidence is largely due to insufficient recovery time being allowed after, for example, a marathon, a triathlon, or other endurance events. Two examples of the incidence of upper respiratory tract illness in moderate versus endurance exercise are provided. In recent years, increasing numbers of research studies have investigated the origins, symptoms, and incidence of these bouts of illness and have attempted to alleviate the symptoms with supplements, sports foods, or immunonutrition. One aspect of the present review discusses iron deficiency, which has been primarily suggested to have an impact upon cell-mediated immunity. Immunonutrition is also discussed, as are new techniques for investigating links between metabolism and immune function.

Presleep Casein Protein Ingestion: Acceleration of Functional Recovery in Professional Soccer Players

PURPOSE

To examine whether consuming casein protein (CP) before sleep would enhance recovery after a nighttime soccer match in professional players.

METHODS

In a randomized, crossover design, 10 professional soccer players from the reserve squad of a team in the highest tier of English soccer consumed 40 g of CP or 40 g of carbohydrates (CON) 30 min presleep after a soccer match (kick off: 7 PM). To assess recovery, countermovement-jump height, reactive strength index, muscle soreness, and the adapted Brief Assessment of Mood (BAM+) Questionnaire were measured before and 12, 36, and 60 h after each match. Dietary intake across the testing period was also recorded.

RESULTS

There were unclear differences in external load in the matches and dietary intake between CON and CP. Casein protein had a most likely and likely beneficial effect on countermovement-jump recovery at 12 and 36 h postmatch (CP -1.6; ±1.2% vs CON -6.6; ±1.7%; -4.1; ±2.3% vs -0.4; ±1.1%, respectively). Reactive strength index recovery was most likely enhanced with CP at 12 and 36 h postmatch, and muscle soreness, as measured with a visual analog scale (in millimeters), was most likely greater in CON versus CP at 12 h postmatch (72; ±17 vs 42; ±20 mm). BAM+ was possibly lower in CON at 36 h postmatch but unaffected at other time points.

CONCLUSIONS

Presleep CP accelerates functional recovery in professional soccer players and, therefore, provides a practical means of attenuating performance deficits in the days after a match.

Photobiomodulation by Led Does Not Alter Muscle Recovery Indicators and Presents Similar Outcomes to Cold-Water Immersion and Active Recovery

Purpose: The aim of the present study was to investigate the effectiveness of photobiomodulation therapy (PBMT) on muscle recovery based on inflammation (interleukin-10 [IL-10]; tumor necrosis factor-α [TNFα]), muscle damage markers (creatine kinase [CK]; lactate dehydrogenase [LDH]), delay onset muscle soreness (DOMS), and countermovement jump performance (CMJ) after two sprint interval training (SIT) sessions compared with a placebo condition (part-I), as well as to compare the effectiveness of PBMT with active recovery (AR) and cold-water immersion (CWI) (part-II). Methods: Part-I was conducted as a double-blind, randomized and placebo-controlled study and part-II as a parallel-group study. Thirty-six men participated in the studies (12 participants in part-I and 36 participants in part-II). Volunteers performed two SITs interspaced by 24-h (SIT₁ and SIT₂) to mimic the effect of accumulating 2 consecutive days of SIT. In part-I, only after SIT₂, PBMT [Total energy: 600J (300J per leg in 5 spots); wavelength: 660-850 nm] or placebo interventions were performed, while in part-II PBMT (part-I data), AR (15-min; 50% of the maximal aerobic power), or CWI (10-min; 10°C) were carried out, also after SIT₂. Blood samples were collected before (i.e., baseline), and 0.5, 1, 24, 48, and 72-h after SIT₂, while CMJ and DOMS were measured before, 24, 48, and 72-h after SIT₂. Results: In part-I, there were no interactions between PBMT and placebo conditions for any blood markers (P ≥ 0.313), DOMS (P = 0.052), and CMJ (P = 0.295). However, an effect of time was found with increases in LDH, CK, and IL-10 (P ≤ 0.043) as well as a decrease in DOMS at 72-h compared with 24-h (P = 0.012). In part-II, there were no interactions between the PBMT, AR, and CWI groups for any markers at the same moments (P ≥ 0.189) and for the peak and integral values (P ≥ 0.193), for DOMS (P = 0.314) and CMJ (P = 0.264). However, an effect of time was found with an increase in CK and IL-10 (P = 0.003), while DOMS decreased at 48 and 72-h compared with 24-h (P = 0.001). Conclusion: In summary, PBMT had no effect on inflammation, muscle damage, CMJ performance, or DOMS after two consecutive sprint interval training sessions compared to placebo, CWI, and AR strategies.

Immunometabolism: A Multi-Omics Approach to Interpreting the Influence of Exercise and Diet on the Immune System

Immunometabolism is an evolving field of scientific endeavor that merges immunology and metabolism and has provided valuable context when evaluating the influence of dietary interventions on exercise-induced immune dysfunction. Metabolomics, lipidomics, and proteomics provide a system-wide view of the metabolic response to exercise by simultaneously measuring and identifying a large number of small-molecule metabolites, lipids, and proteins. Many of these are involved with immune function and regulation and are sensitive to dietary influences, especially acute carbohydrate ingestion from either sugar beverages or fruits such as bananas. Emerging evidence using large multi-omics data sets supports the combined intake of fruit sugars and phytochemicals by athletes during heavy exertion as an effective strategy to improve metabolic recovery, augment viral defense, and counter postexercise inflammation and immune dysfunction at the cell level. Multi-omics methodologies have given investigators new outcome targets to assess the efficacy of various dietary interventions for physiologically stressed athletes.

Nutritional and Supplementation Strategies to Prevent and Attenuate Exercise-Induced Muscle Damage: a Brief Review

Exercise-induced muscle damage (EIMD) is typically caused by unaccustomed exercise and results in pain, soreness, inflammation, and reduced muscle function. These negative outcomes may cause discomfort and impair subsequent athletic performance or training quality, particularly in individuals who have limited time to recover between training sessions or competitions. In recent years, a multitude of techniques including massage, cryotherapy, and stretching have been employed to combat the signs and symptoms of EIMD, with mixed results. Likewise, many varied nutritional and supplementation interventions intended to treat EIMD-related outcomes have gained prominence in the literature. To date, several review articles have been published that explore the many recovery strategies purported to minimize indirect markers of muscle damage. However, these articles are very limited from a nutritional standpoint. Thus, the purpose of this review is to briefly and comprehensively summarize many of these strategies that have been shown to positively influence the recovery process after damaging exercise. These strategies have been organized into the following sections based on nutrient source: fruits and fruit-derived supplements, vegetables and plant-derived supplements, herbs and herbal supplements, amino acid and protein supplements, vitamin supplements, and other supplements.

Effects of acute grape seed extract supplementation on muscle damage after eccentric exercise: A randomized, controlled clinical trial

Background/objective

High intensity eccentric exercise causes muscle damage. Polyphenol supplementation is one nutritional intervention available to limit muscle damage, but there is a lack of published data concerning the use of polyphenol-rich grape seed extract (GSE). This study investigated the effect of acute GSE supplementation on muscle damage markers after eccentric exercise.

Methods

Sixteen healthy male university students (mean age: 20.3 ± 0.4 years, height: 176.1 ± 4.7 cm, weight: 69.9 ± 10.2 kg) were included. Participants were randomly assigned to GSE group (n = 8) or placebo group (n = 8); 300 mg/day of GSE or placebo was consumed from the time of eccentric exercise to 72 h after exercise. For the eccentric exercise, the elbow flexor muscle was activated using a modified preacher curl machine at 25 repetitions for 2 sets. For the muscle damage markers, maximal muscle strength, muscle soreness, and creatine kinase (CK) level were measured.

Results

There was no difference in maximal muscle strength and muscle soreness between groups in the recovery stage after eccentric exercise (p > 0.05); CK level, a marker of cell membrane damage, was significantly decreased 96 h after exercise in the GSE group compared with the placebo group (p < 0.05).

Conclusion

Acute GSE supplement can be an effective way to decrease cellular membrane damage after eccentric exercise. These results could be helpful in the application of GSE supplementation as a nutritional intervention to reduce muscle damage after high intensity strength training, especially in the early stage of a new strength training program. However, a larger scale study is necessary to validate these results.

Impact of heat therapy on recovery after eccentric exercise in humans

The purpose of this study was to investigate the effects of heat therapy (HT) on functional recovery, the skeletal muscle expression of angiogenic factors, macrophage content, and capillarization after eccentric exercise in humans. Eleven untrained individuals (23.8 ± 0.6 yr) performed 300 bilateral maximal eccentric contractions of the knee extensors. One randomly selected thigh was treated with five daily 90-min sessions of HT, whereas the opposite thigh received a thermoneutral intervention. Peak isokinetic torque of the knee extensors was assessed at baseline and daily for 4 days and fatigue resistance was assessed at baseline and 1 and 4 days after the eccentric exercise session. Muscle biopsies were obtained 2 wk before and 1 and 5 days after the eccentric exercise bout. There were no differences between thighs in the overall recovery profile of peak torque. However, the thigh exposed to HT had greater fatigue resistance than the thigh exposed to the thermoneutral intervention. The change from baseline in mRNA expression of vascular endothelial growth factor (VEGF) was higher at day 1 in the thigh exposed to HT. Protein levels of VEGF and angiopoietin 1 were also significantly higher in the thigh treated with HT. The number of capillaries around type II fibers decreased similarly in both thighs at day 5. Exposure to HT had no impact on macrophage content. These results suggest that HT accelerates the recovery of fatigue resistance after eccentric exercise and promotes the expression of angiogenic factors in human skeletal muscle. NEW & NOTEWORTHY We investigated whether exposure to local heat therapy (HT) accelerates recovery after a bout of eccentric exercise in humans. Compared with a thermoneutral control intervention, HT improved fatigue resistance of the knee extensors and enhanced the expression of the angiogenic mediators vascular endothelial growth factor and angiopoietin 1. These results suggest that HT hastens functional recovery and enhances the expression of regulatory factors involved in muscle repair after eccentric exercise in humans.

Effects of oat protein supplementation on skeletal muscle damage, inflammation and performance recovery following downhill running in untrained collegiate men

The positive influence of animal-based protein supplementation during muscle-damaging exercise has been widely studied. However, the effects of plant-based proteins remain unclear and require further clarification. This study investigated the protective role of oat protein against exercise induced muscle damage (EIMD), subsequent inflammation, and loss of performance induced by downhill running. Subjects consumed either oat protein (25 g protein) or a placebo for 14 days prior to a downhill running test and then for 4 days thereafter. Treatments with oat protein for 19 days markedly alleviated eccentric exercise induced skeletal muscle soreness, and reduced the elevation of plasma IL-6 concentrations and serum creatine kinase, myoglobin and C reactive protein contents. In addition, oat protein supplementation significantly inhibited limb edema following damaging exercise, and the adverse effects on muscle strength, knee-joint range of motion, and vertical jump performance were lessened. Furthermore, the administration of oat protein facilitated recovery from exhaustive downhill running in this study. These findings demonstrated that oat protein supplementation has the potential to alleviate the negative effects of eccentric exercise in untrained young males.

Acute and Delayed Neuromuscular Alterations Induced by Downhill Running in Trained Trail Runners: Beneficial Effects of High-Pressure Compression Garments

Introduction: The aim of this study was to examine, from a crossover experimental design, whether wearing high-pressure compression garments (CGs) during downhill treadmill running affects soft-tissue vibrations, acute and delayed responses in running economy (RE), neuromuscular function, countermovement jump, and perceived muscle soreness. Methods: Thirteen male trail runners habituated to regular eccentric training performed two separate 40-min downhill running (DHR, -8.5°) sessions while wearing either CGs (15-20 mmHg for quadriceps and calves) or control garments (CON) at a velocity associated with ∼55% of VO2max , with a set of measurements before (Pre-), after (Post-DHR), and 1 day after (Post-1D). No CGs was used within the recovery phase. Perceived muscle soreness, countermovement jump, and neuromuscular function (central and peripheral components) of knee extensors (KE) and plantar flexors (PF) were assessed. Cardiorespiratory responses (e.g., heart rate, ventilation) and RE, as well as soft-tissue vibrations (root mean square of the resultant acceleration, RMS Ar ) for vastus lateralis and gastrocnemius medialis were evaluated during DHR and in Post-1D. Results: During DHR, mean values in RMS Ar significantly increased over time for the vastus lateralis only for the CON condition (+11.6%). RE and cardiorespiratory responses significantly increased (i.e., alteration) over time in both conditions. Post, small to very large central and peripheral alterations were found for KE and PF in both conditions. However, the deficit in voluntary activation (VA) was significantly lower for KE following CGs (-2.4%), compared to CON (-7.9%) conditions. No significant differences in perceived muscle soreness and countermovement jump were observed between conditions whatever the time period. Additionally, in Post-1D, the CGs condition showed reductions in neuromuscular peripheral alterations only for KE (from -4.4 to -7.7%) and perceived muscle soreness scores (-8.3%). No significant differences in cardiorespiratory and RE responses as well as countermovement jump were identified between conditions in Post-1D. Discussion: Wearing high-pressure CGs (notably on KE) during DHR was associated with beneficial effects on soft-tissue vibrations, acute and delayed neuromuscular function, and perceived muscle soreness. The use of CGs during DHR might contribute to the enhanced muscle recovery by exerting an exercise-induced "mechanical protective effect."

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.

Syzygium cumini Nectar Supplementation Reduced Biomarkers of Oxidative Stress, Muscle Damage, and Improved Psychological Response in Highly Trained Young Handball Players

The purpose of this study was to investigate the effects of Syzygium cumini (SC) nectar supplementation on performance, markers of oxidative stress, muscle damage, and psychological response in Handball players. Twenty-five young athletes (age = 18.6 ± 2.4 years) from an elite high school national level Brazilian Handball team were randomized into two study groups: SC/Jamelon nectar (SC, n = 12) and placebo (n = 13). The subjects ingested 10 mL/kg/day of Jamelon nectar or placebo 30 min before the training sessions and immediately after training cessation, for 28 days. Body mass index (BMI) and percentage of fat mass were assessed using bioelectrical impedance analysis. Biomarkers of oxidative stress were measured by lipid peroxidation, which was quantified by malondialdehyde (MDA). Total antioxidant capacity (TAC), creatine kinase (CK) activity, and lactate dehydrogenase (LDH) were determined. The 20 m shuttle run test, vertical jump, and running anaerobic sprint test were assessed to verify performance and the fatigue index was calculated. The Profile of Mood States (POMS) questionnaire was used for psychological evaluation. Both groups demonstrated improved vertical jump performance and a decreased fatigue index over time but without significant differences between them regarding performance. There was statistically significance only for SC in CK, LDH, and MDA, and TAC was greater in the SC compared to placebo. Furthermore, only the SC group demonstrated improved mood disturbance and confusion after the intervention. In conclusion, the present study suggests that SC nectar supplementation reduced biomarkers of oxidative stress and muscle damage, and improved psychological response in young handball players.

Stimuli and sensors that initiate skeletal muscle hypertrophy following resistance exercise

One of the most striking adaptations to exercise is the skeletal muscle hypertrophy that occurs in response to resistance exercise. A large body of work shows that a mammalian target of rapamycin complex 1 (mTORC1)-mediated increase of muscle protein synthesis is the key, but not sole, mechanism by which resistance exercise causes muscle hypertrophy. While much of the hypertrophy signaling cascade has been identified, the initiating, resistance exercise-induced and hypertrophy-stimulating stimuli have remained elusive. For the purpose of this review, we define an initiating, resistance exercise-induced and hypertrophy-stimulating signal as "hypertrophy stimulus," and the sensor of such a signal as "hypertrophy sensor." In this review we discuss our current knowledge of specific mechanical stimuli, damage/injury-associated and metabolic stress-associated triggers, as potential hypertrophy stimuli. Mechanical signals are the prime hypertrophy stimuli candidates, and a filamin-C-BAG3-dependent regulation of mTORC1, Hippo, and autophagy signaling is a plausible albeit still incompletely characterized hypertrophy sensor. Other candidate mechanosensing mechanisms are nuclear deformation-initiated signaling or several mechanisms related to costameres, which are the functional equivalents of focal adhesions in other cells. While exercise-induced muscle damage is probably not essential for hypertrophy, it is still unclear whether and how such muscle damage could augment a hypertrophic response. Interventions that combine blood flow restriction and especially low load resistance exercise suggest that resistance exercise-regulated metabolites could be hypertrophy stimuli, but this is based on indirect evidence and metabolite candidates are poorly characterized.

The Role of Inflammation and Immune Cells in Blood Flow Restriction Training Adaptation: A Review

Blood flow restriction (BFR) combined with low-intensity strength training has been shown to increase skeletal muscle mass and strength in a variety of populations. BFR results in a robust metabolic stress which is hypothesized to induce muscle growth via increased recruitment of fast-twitch muscle fibers, a greater endocrine response, and/or enhancing the cellular swelling contribution to the hypertrophic process. Following exercise, neutrophils are the first immune cells to initiate the tissue remodeling process via several mechanisms including an increased production of cytokines and recruitment of monocytes/macrophages, which facilitate the phagocytosis of foreign particles, the differentiation of myoblasts, and the formation of new myotubes. Thus, the purpose of this review was to discuss the mechanisms through which metabolic stress and immune cell recruitment may induce skeletal muscle remodeling following BFR strength training.

Reduction of Real-Time Imaging of M1 Macrophage Chemotaxis toward Damaged Muscle Cells is PI3K-Dependent

Macrophages migrate and invade into damaged muscle rapidly and are important for muscle repair and subsequent regeneration. The exact cellular and biological events that cause macrophage migration toward injured muscle are not completely understood. In this study, the effect of macrophage differentiation on the chemotactic capability to invade local damaged muscle was investigated using an in vitro model of muscle injury. We used C2C12 cell myoblasts and J774 cell macrophages, and the "killed-C2C12" cells were combined with live C2C12 cells as a partially damaged muscle model. The cultured J774 cells, with or without lipopolysaccharide (LPS), were treated with Ly294002 (Ly), which is an inhibitor of phosphoinositide 3-kinase (PI3K). In order to evaluate the polarization effect of LPS stimulation on J774 cells, expression of cell surface Toll-like receptor 4 (TLR4), CD11c and CCR2, and expression of F-actin intensity, were analyzed by flow cytometry. The real-time horizontal chemotaxis assay of J774 cells was tested using the TAXIScan device. The expressions of TLR4, CD11c, and F-actin intensity in LPS-treated cells were significantly higher than those in Ctrl cells. In LPS-treated cells, the chemotactic activity toward damaged muscle cells completely disappeared. Moreover, the reduced chemotaxis depended far more on directionality than velocity. However, Ly treatment reversed the reduced chemotactic activity of the LPS-treated cells. In addition, cell-adhesion and F-actin intensity, but not CCR2 expression, in LPS-treated cells, was significantly reduced by Ly treatment. Taken together, our results suggest that the PI3K/Akt activation state drives migration behavior towards damaged muscle cells.

Age-specific response of skeletal muscle extracellular matrix to acute resistance exercise: A pilot study

The extracellular matrix (ECM) plays an essential role in the development, growth and repair of skeletal muscles and serves to transmit contractile force. However, its regulation is poorly understood. This study investigates the age-specificity of the effects of acute resistance exercise on ECM gene expression. To this purpose, five young (YM, 23.8 ± 2.2 yrs.) and 5 elderly (EM, 66.8 ± 4.1 yrs.) men performed one session of unilateral leg press and leg extension exercises. Six hours post-exercise, biopsies were taken from the vastus lateralis muscles of both legs. A PCR array was used to profile the expression of 84 ECM-related genes, of which 6 were validated by qPCR. The PCR array found 9 and 4 ECM-associated genes to be selectively altered (>1.5-fold change) in YM or EM only. Four further genes were upregulated in YM but downregulated in EM. Of the 6 genes validated on individual samples MMP9 expression increased in YM (9.7-fold) and decreased (0.2-fold) in EM. MMP15 was downregulated in EM only (0.6-fold). A significant correlation between leg extension 1 RM and changes in COL7A1 expression (ρ = 0.71) suggests a potential influence of fitness levels. In conclusion, acute resistance exercise affects ECM gene expression at least partly in an age-specific manner. The altered expression of genes encoding matrix metalloproteinases (MMP3, MMP9, MMP15) highlights the role of remodelling processes in the response to an acute bout of resistance exercise. Larger studies are required to verify the age-associated differences in gene expression profiles and establish their functional implications.

Involvement of Neutrophil Dynamics and Function in Exercise-Induced Muscle Damage and Delayed-Onset Muscle Soreness: Effect of Hydrogen Bath

The purpose of this study was to investigate the involvement of neutrophil dynamics and function in exercise-induced muscle damage (EIMD) and delayed-onset muscle soreness (DOMS), and the effect of molecular hydrogen (H₂) intake on these parameters. Nine healthy and active young men performed H₂ and placebo bath trial in a crossover design. They carried out downhill running (−8% slope) for 30 min at a speed corresponding to 75~85% of peak oxygen uptake (VO₂peak). Subsequently, they repeated bathing for 20 min per day for one week. Degree of muscle soreness (visual analogue scale: VAS), peripheral leukocyte counts, neutrophil dynamics and function, muscle damage, and inflammation markers were measured. Plasma interleukin (IL)-6 concentration was significantly correlated with peripheral neutrophil count, VAS, and serum creatine kinase activity, respectively, after downhill running. Peripheral neutrophil count and serum myoglobin concentration were also significantly correlated. Conversely, there were no effects of H₂ bath. These results suggest that IL-6 may be involved in the mobilization of neutrophils into the peripheral blood and subsequent EIMD and DOMS after downhill running; however, it is not likely that H₂ bath is effective for the inflammatory process that is centered on neutrophils after downhill running.

Detection of Functional Overreaching in Endurance Athletes Using Proteomics

No reliable biomarkers exist to identify athletes in various training states including functional overreaching (FOR), non-functional overreaching (NFOR), and overtraining syndrome (OTS). Participants (N = 10, age 38.3 ± 3.4 years) served as their own controls and in random, counterbalanced order either ran/cycled 2.5 h (70.0 ± 3.7% VO_2max) three days in a row (FOR) or sat in the lab (rest) (separated by three weeks; 7:00–9:30 am, overnight fasted state). Participants provided fingerprick samples for dried blood spot samples (DBS) pre- and post-exercise/rest, and then during two recovery days. DBS proteins were measured with nanoLC-MS in data-independent acquisition (DIA) mode, and 593 proteins were identified and quantified. Proteins were considered for the FOR cluster if they were elevated during one of the two recovery days but not more than one of the exercise days (compared to rest). The generalized estimating equation (GEE) was used to identify proteins linked to FOR. A total of 13 proteins was linked to FOR and most were associated with the acute phase response and innate immune system activation. This study used a system-wide proteomics approach to define a targeted panel of blood proteins related to FOR that could form the basis of future NFOR- and OTS-based studies.

Eccentric Training Improves Body Composition by Inducing Mechanical and Metabolic Adaptations: A Promising Approach for Overweight and Obese Individuals

Skeletal muscle generates force by either shortening (concentrically) or lengthening (eccentrically). Eccentric (ECC) exercise is characterized by a lower metabolic demand and requires less muscle activity than concentric (CON) exercise at the same level of exerted force. However, the specific effect of ECC training vs. CON training on lean and fat mass remains underexplored. The first aim of this paper was to review the available evidence regarding the effects of ECC training on whole body and segmental lean and fat mass and, when possible, compare these with the effects of CON training. The second aim was to provide some insights into the main mechanical, physiological, and metabolic adaptations of ECC training that contribute to its effects on body composition. The third aim was to determine the beneficial effects of ECC exercise on health-related parameters in overweight and obese patients. ECC training is an effective modality to improve lean mass, but when matched for load or work, the difference between ECC and CON trainings seems unclear. A few studies reported that ECC training is also efficient at reducing fat mass. By increasing post-exercise resting energy expenditure, modifying metabolic substrate, and improving both blood lipid profile and insulin resistance, ECC training is a potential exercise modality for individuals with chronic conditions such as those who are overweight and obese. Further investigations using standardized experimental conditions, examining not only segmental but also whole body composition, are required to compare ECC and CON trainings.

The Psychophysiological Regulation of Pacing Behaviour and Performance Fatigability During Long-Distance Running with Locomotor Muscle Fatigue and Exercise-Induced Muscle Damage in Highly Trained Runners

BACKGROUND

Locomotor muscle fatigue (LMMF) and exercise-induced muscle damage (EIMD) are common conditions experienced during long-distance running due to the pooled effect of mechanical and metabolic strain on the locomotor muscles. However, little is known about the instant effects of combined LMMF and EIMD on pacing behaviour and performance during the decisive final stages of 'real-world' long-distance running events.

METHODS

Twenty-two highly trained runners (11 females) completed two maximal self-paced 20-km treadmill time trials in a counterbalanced crossover design: (A) in a tapered condition and (B) with LMMF and EIMD. Indicators of muscle damage, muscle metabolic strain, and endocrinological stress were assessed to investigate the physiological effects, and a three-dimensional framework of perceived fatigability was applied to investigate the perceptual effects of running with LMMF and EIMD on performance fatigability.

RESULTS

LMMF and EIMD caused restrictions in work capacity and medium increases in blood leucocyte and neutrophil count, interleukin-6, and cortisol concentrations, collectively constituting a physiological milieu likely not conducive to high performance. LMMF and EIMD further caused large increases in perceived physical strain and large decreases in valence as well as large increases and decreases in action crisis and flow state, respectively.

CONCLUSIONS

Under the constraint of amplified physical duress, findings are suggestive of heuristic and rational antecedents in the goal disengagement process. Dynamic changes in physiological and perceptual effects of LMMF and EIMD are hypothesised to underpin the observed alterations in pacing behaviour and performance fatigability during long-distance running. The applied three-dimensional framework provides a more comprehensive understanding of strain-perception-thinking-action coupling in centrally regulated and goal-directed exercise behaviour.

Adding omega-3 fatty acids to a protein-based supplement during pre-season training results in reduced muscle soreness and the better maintenance of explosive power in professional Rugby Union players

Evidence suggests that omega-3 fatty acid supplementation could reduce muscle soreness and maintain muscle function following eccentric exercise-induced muscle damage. The aim of this applied field study was to investigate the effectiveness of consuming a protein-based supplement containing 1546 mg of omega-3 polyunsaturated fatty acid (PUFA) (551 mg eicosapentaenoic acid (EPA) and 551 mg docosahexaenoic acid (DHA)) twice daily (FO) compared to a protein-based placebo (P) on muscle soreness, countermovement jump (CMJ) performance and psychological well-being in 20 professional Rugby Union players during 5 weeks of pre-season training. Players completed a 5-point-Likert soreness scale with 5 indicating "no soreness" and a questionnaire assessing fatigue, sleep, stress and mood each morning of training, plus they performed CMJ tests once or twice per week. Data were analysed using magnitude-based inferential statistics and are presented as percent beneficial/trivial/harmful. On day 35, there was a likely (% beneficial/trivial/harmful: 94/5/1) moderate (0.75, standardized mean difference (SMD)) beneficial effect of FO vs. P on the change in lower body muscle soreness compared with day 0 (FO: -3.8 ± 21.7%; P: -19.4 ± 11.2%). There was a likely (92/7/0) moderate (SMD: 0.60) beneficial effect of FO vs. P on CMJ performance (change from baseline to day 35, FO: +4.6 ± 5.9%; P: -3.4 ± 8.6%). From day 20, a moderate beneficial effect of FO on fatigue was observed. In terms of practical relevance, the moderate beneficial effect of adding fish oil to a protein-based supplement on muscle soreness translated into the better maintenance of explosive power in elite Rugby Union players during pre-season training.

A novel biomarker explaining the role of oxidative stress in exercise and l-tyrosine supplementation: thiol/disulphide homeostasis

The present study aimed to evaluate the relationship between exercise and both l-tyrosine and oxidative stress using thiol/disulphide homeostasis via a novel biomarker in rats. Following the completion of the exercise and l-tyrosine protocol, serum total thiol, native thiol, and disulphide concentrations were determined using a novel automated measurement method. Compared with the control group, serum dynamic disulphide levels were significantly lower in the E group (116.75 ± 10.49; p < .05) and the highest in the LT group (151.0 ± 5.84). The lowest oxidised thiol (49.75 ± 6.18; p = .087) and the highest reduced thiol (75.38 ± 3.16; p = .079) rates were determined to be in the E group. The highest oxidised thiol value was observed in the LT group. Exercise positively affects thiol/disulphide homeostasis, which is a novel indicator of oxidant-antioxidant parameters. Additionally, l-tyrosine appears to be more convenient combined with exercise. The new method used in our study proposes a promising, practical, and useful method for assessing the oxidative stress parameters.

Exertional Rhabdomyolysis after an Extreme Conditioning Competition: A Case Report

This case report describes an instance of exercise-induced rhabdomyolysis caused by an extreme conditioning program (ECP) competition. A 35-year-old female presented with abdominal pain and soreness, which began one day after she completed two days of ECPcompetition composed of five workouts. Three days after competition, creatine kinase (CK) was 77,590 U/L accompanied by myalgia and abnormal liver function tests, while renal function was normal and this resulted in a diagnosis of rhabdomyolysis. A follow-up examination revealed that her serum level of CK was still elevated to 3034 U/L on day 10 and 1257 U/L on day 25 following the ECP competition. The subject reported myalgia even up to 25 days after the ECP competition. Exertional rhabdomyolysis can be observed in ECP athletes following competition and highlights a dangerous condition, which may be increasing in recent years due to the massive expansion of ECP popularity and a growing number of competitions. Future research should investigate the causes of rhabdomyolysis that occur as a result of ECP, especially training methods and/or tasks developed specifically for these competitions.

Arachidonic acid supplementation transiently augments the acute inflammatory response to resistance exercise in trained men

Strenuous exercise can result in skeletal muscle damage, leading to the systemic mobilization, activation, and intramuscular accumulation of blood leukocytes. Eicosanoid metabolites of arachidonic acid (ARA) are potent inflammatory mediators, but whether changes in dietary ARA intake influence exercise-induced inflammation is not known. This study investigated the effect of 4 wk of dietary supplementation with 1.5 g/day ARA ( n = 9, 24 ± 1.5 yr) or corn-soy oil placebo ( n = 10, 26 ± 1.3 yr) on systemic and intramuscular inflammatory responses to an acute bout of resistance exercise (8 sets each of leg press and extension at 80% one-repetition maximum) in previously trained men. Whole EDTA blood, serum, peripheral blood mononuclear cells (PMBCs), and skeletal muscle biopsies were collected before exercise, immediately postexercise, and at 2, 4, and 48 h of recovery. ARA supplementation resulted in higher exercise-stimulated serum creatine kinase activity [incremental area under the curve (iAUC) P = 0.046] and blood leukocyte counts (iAUC for total white cells, P < 0.001; neutrophils: P = 0.007; monocytes: P = 0.015). The exercise-induced fold change in peripheral blood mononuclear cell mRNA expression of interleukin-1β ( IL1B), CD11b ( ITGAM), and neutrophil elastase ( ELANE), as well as muscle mRNA expression of the chemokines interleukin-8 ( CXCL8) and monocyte chemoattractant protein 1 ( CCL2) was also greater in the ARA group than placebo. Despite this, ARA supplementation did not influence the histological presence of leukocytes within muscle, perceived muscle soreness, or the extent and duration of muscle force loss. These data show that ARA supplementation transiently increased the inflammatory response to acute resistance exercise but did not impair recovery. NEW & NOTEWORTHY Daily arachidonic acid supplementation for 4 wk in trained men augmented the acute systemic and intramuscular inflammatory response to a subsequent bout of resistance exercise. Greater exercise-induced inflammatory responses in men receiving arachidonic acid supplementation were not accompanied by increased symptoms of exercise-induced muscle damage. Although increased dietary arachidonic acid intake does not appear to influence basal inflammation in humans, the acute inflammatory response to exercise stress is transiently increased following arachidonic acid supplementation.

Collision activity during training increases total energy expenditure measured via doubly labelled water

PURPOSE

Collision sports are characterised by frequent high-intensity collisions that induce substantial muscle damage, potentially increasing the energetic cost of recovery. Therefore, this study investigated the energetic cost of collision-based activity for the first time across any sport.

METHODS

Using a randomised crossover design, six professional young male rugby league players completed two different 5-day pre-season training microcycles. Players completed either a collision (COLL; 20 competitive one-on-one collisions) or non-collision (nCOLL; matched for kinematic demands, excluding collisions) training session on the first day of each microcycle, exactly 7 days apart. All remaining training sessions were matched and did not involve any collision-based activity. Total energy expenditure was measured using doubly labelled water, the literature gold standard.

RESULTS

Collisions resulted in a very likely higher (4.96 ± 0.97 MJ; ES = 0.30 ± 0.07; p = 0.0021) total energy expenditure across the 5-day COLL training microcycle (95.07 ± 16.66 MJ) compared with the nCOLL training microcycle (90.34 ± 16.97 MJ). The COLL training session also resulted in a very likely higher (200 ± 102 AU; ES = 1.43 ± 0.74; p = 0.007) session rating of perceived exertion and a very likely greater (- 14.6 ± 3.3%; ES = - 1.60 ± 0.51; p = 0.002) decrease in wellbeing 24 h later.

CONCLUSIONS

A single collision training session considerably increased total energy expenditure. This may explain the large energy expenditures of collision-sport athletes, which appear to exceed kinematic training and match demands. These findings suggest fuelling professional collision-sport athletes appropriately for the "muscle damage caused" alongside the kinematic "work required".