Exercise-induced muscle damage and the potential protective role of estrogen

Creatine kinase isoenzyme activity during and after an ultra-distance (200 km) run

It is commonly assumed that creatine kinase (CK) activity in plasma is related to the state of an inflammatory response at 24-48 h, and also it has shown biphasic patterns after a marathon run. No information is available on CK isoenzymes after an ultra-marathon run. The purpose of the present study is to examine the CK isoenzymes after a 200 km ultra-marathon run and during the subsequent recovery. Blood samples were obtained during registration 1 2 h before the 200-km race and during the race at 100 km, 150 km and at the end of 200 km, as well as after a 24 h period of recovery. Thirty-two male ultra-distance runners participated in the study. Serum CPK showed a marked increase throughout the race and 24 h recovery period (p < 0.001). Serum CK during the race occurs mostly in the CK-MM isoform and only minutely in the CK-MB isoform and is unchanged in the CK-BB isoform. High-sensitivity C-reactive protein (hs-CRP), oestradiol, AST and ALT increased significantly from the pre-race value at 100 km and a further increase took place by the end of the 200 km run. The results of our study demonstrate a different release pattern of creatine kinase after an ultra-distance (200 km) run compared to the studies of marathon running and intense eccentric exercise, and changes in several biomarkers, indicative of muscle damage during the race, were much more pronounced during the latter half (100–200 km) of the race. However, the increases in plasma concentration of muscle enzymes may reflect not only structural damage, but also their rate of clearance.

Alterations in redox homeostasis in the elite endurance athlete

BACKGROUND

The production of reactive oxygen (ROS) and nitrogen species (RNS) is a fundamental feature of mammalian physiology, cellular respiration and cell signalling, and essential for muscle function and training adaptation. Aerobic and anaerobic exercise results in alterations in redox homeostasis (ARH) in untrained, trained and well trained athletes. Low to moderate doses of ROS and RNS play a role in muscle adaptation to endurance training, but an overwhelming increase in RNS and ROS may lead to increased cell apoptosis and immunosuppression, fatigued states and underperformance.

OBJECTIVES

The objectives of this systematic review are: (a) to test the hypotheses that ARH occur in elite endurance athletes; following an acute exercise bout, in an endurance race or competition; across a micro-, meso- or macro-training cycle; following a training taper; before, during and after altitude training; in females with amenorrhoea versus eumenorrhoea; and in non-functional over-reaching (NFOR) and overtraining states (OTS); (b) to report any relationship between ARH and training load and ARH and performance; and (c) to apply critical difference values for measures of oxidative stress/ARH to address whether there is any evidence of ARH being of physiological significance (not just statistical) and thus relevant to health and performance in the elite athlete.

METHODS

Electronic databases, Embase, MEDLINE, and SPORTDiscus were searched for relevant articles. Only studies that were observational articles of cross-sectional or longitudinal design, and included elite athletes competing at national or international level in endurance sports were included. Studies had to include biomarkers of ARH; oxidative damage, antioxidant enzymes, antioxidant capacity, and antioxidant vitamins and nutrients in urine, serum, plasma, whole blood, red blood cells (RBCs) and white blood cells (WBCs). A total of 3,057 articles were identified from the electronic searches. Twenty-eight articles met the inclusion criteria and were included in the review.

RESULTS

ARH occurs in elite endurance athletes, after acute exercise, a competition or race, across training phases, and with natural or simulated altitude. A reduction in ARH occurs across the season in elite athletes, with marked variation around intensified training phases, between individuals, and the greatest disturbances (of physiological significance) occurring with live-high-train-low techniques, and in athletes competing. A relationship with ARH and performance and illness exists in elite athletes. There was considerable heterogeneity across the studies for the biomarkers and assays used; the sport; the blood sampling time points; and the phase in the annual training cycle and thus baseline athlete fitness. In addition, there was a consistent lack of reporting of the analytical variability of the assays used to assess ARH.

CONCLUSIONS

The reported biochemical changes around ARH in elite athletes suggest that it may be of value to monitor biomarkers of ARH at rest, pre- and post-simulated performance tests, and before and after training micro- and meso-cycles, and altitude camps, to identify individual tolerance to training loads, potentially allowing the prevention of non-functionally over-reached states and optimisation of the individual training taper and training programme.

The effect of milk on the attenuation of exercise-induced muscle damage in males and females

PURPOSE

The consumption of 500 ml milk following muscle damaging exercise can attenuate decreases in muscle functional capacity and increases in markers of muscle damage and soreness in males. There has been no similar research in female participants. Therefore, the aim of this study was to investigate the effects of milk consumption on exercise-induced muscle damage (EIMD) in males and females.

METHODS

Thirty-two team sport players (male n = 16; female n = 16) were randomly, but equally divided into four groups: male milk, male carbohydrate, female milk, and female carbohydrate. Immediately following muscle damaging exercise, participants consumed either 500 ml of milk or 500 ml of an energy-matched carbohydrate solution. Skeletal troponin I (sTnI), creatine kinase (CK), peak torque, counter movement jump height, 20 m sprint performance and passive and active soreness were recorded prior to and 24, 48 and 72 h post-EIMD.

RESULTS

For females, milk had a likely/very likely beneficial effect on attenuating losses in peak torque at 60°/s from baseline to 24, 48 and 72 h, and a likely beneficial effect in minimising decrements in sprint performance and soreness over 72 h. Milk was unlikely to have a negative effect on serum markers of damage from baseline to 48 and 72 h. For males, milk had an unclear effect on muscle function variables. Milk had a most likely/likely beneficial effect on limiting muscle soreness from baseline to 72 h, and a possible beneficial effect on attenuating increases in CK. The effect on sTnI was unlikely to be negative from baseline-72 h. Overall gender comparisons provided many unclear outcomes. However, female participants demonstrated smaller increases in sprint time, passive soreness, active soreness (non-dominant leg) and sTnI values.

CONCLUSION

Consumption of 500 ml of milk post-EIMD can limit decrements in muscle function in females, and limit increases in soreness and serum markers of muscle damage in females and males.

Hepatoprotective effect of 17β-estradiol as antioxidant modulators against stress damage

BACKGROUND

Liver is one of the most important organs affected by exercise. According to the literature a few study to date has investigated the effects of estrogen supplementation on exercise-induced oxidative stress in liver tissue of rats.

OBJECTIVES

We aimed to investigate the effects of estrogen supplementation on oxidative stress markers in liver tissue of exercised rats.

MATERIALS AND METHODS

Male rats (n = 35) were divided as estrogen supplemented (n = 18) and non-supplemented groups (n = 17); these groups were further divided as rest and eccentric exercised groups. Eccentric exercise groups were further divided as rats killed after 1 hour and 48 hours of eccentric exercise. Estrogen (10 mg/kg) was administered subcutaneously for 30 days. Eccentric exercise was applied as treadmill run (15° downhill, 20 m/min) consisting of periods of "5 min" run and 2 min rest repeated 18 times. The rat liver was examined biochemically and histologically. Activities of GST, GSH-Px, CAT, SOD and MDA concentration were also measured spectrophotometrically.

RESULTS

Some disruptions were detected in experimental groups compared with the control group. Additionally, exercise training caused an increase in SOD and decrease in GSH-Px activities in some experimental groups. SOD activities increased significantly in group 3 (Estrogen (-), eccentric exercise (+) killed (after 1 h), compared with group 5 (Estrogen (-), eccentric exercise (+) killed (after 48 h). On the other hand, GSH-Px activities were also significantly decreased in groups 3, 4 and 5 compared with the control group. Leukocyte infiltration in liver increased after 48 hours compared with after 1 hour and estrogen supplementation was not able to prevent this infiltration.

CONCLUSIONS

Estrogen seemed to be not very effective to prevent eccentric exercise-induced liver damage.

Mechanisms and efficacy of heat and cold therapies for musculoskeletal injury

Nonpharmacological treatment strategies for acute musculoskeletal injury revolve around pain reduction and promotion of healing in order to facilitate a return to normal function and activity. Heat and cold therapy modalities are often used to facilitate this outcome despite prevalent confusion about which modality (heat vs cold) to use and when to use it. Most recommendations for the use of heat and cold therapy are based on empirical experience, with limited evidence to support the efficacy of specific modalities. This literature review provides information for practitioners on the use of heat and cold therapies based on the mechanisms of action, physiological effects, and the medical evidence to support their clinical use. The physiological effects of cold therapy include reductions in pain, blood flow, edema, inflammation, muscle spasm, and metabolic demand. There is limited evidence from randomized clinical trials (RCTs) supporting the use of cold therapy following acute musculoskeletal injury and delayed-onset muscle soreness (DOMS). The physiological effects of heat therapy include pain relief and increases in blood flow, metabolism, and elasticity of connective tissues. There is limited overall evidence to support the use of topical heat in general; however, RCTs have shown that heat-wrap therapy provides short-term reductions in pain and disability in patients with acute low back pain and provides significantly greater pain relief of DOMS than does cold therapy. There remains an ongoing need for more sufficiently powered high-quality RCTs on the effects of cold and heat therapy on recovery from acute musculoskeletal injury and DOMS.

Acute resistance exercise increases the expression of chemotactic factors within skeletal muscle

INTRODUCTION

Intense resistance exercise causes mechanical loading of skeletal muscle, followed by muscle adaptation. Chemotactic factors likely play an important role in these processes.

PURPOSE

We investigated the time course of changes in the expression and tissue localization of several key chemotactic factors in skeletal muscle during the early phase of recovery following resistance exercise.

METHODS

Muscle biopsy samples were obtained from vastus lateralis of eight untrained men (22 ± 0.5 years) before and 2, 4 and 24 h after three sets of leg press, squat and leg extension at 80 % 1-RM.

RESULTS

Monocyte chemotactic protein-1 (95×), interleukin-8 (2,300×), IL-6 (317×), urokinase-type plasminogen activator (15×), vascular endothelial growth factor (2×) and fractalkine (2.5×) mRNA was significantly elevated 2 h post-exercise. Interleukin-8 (38×) and interleukin-6 (58×) protein was also significantly elevated 2 h post-exercise, while monocyte chemotactic protein-1 protein was significantly elevated at 2 h (22×) and 4 h (21×) post-exercise. Monocyte chemotactic protein-1 and interleukin-8 were expressed by cells residing in the interstitial space between muscle fibers and, in some cases, were co-localized with CD68 + macrophages, PAX7 + satellite cells and blood vessels. However, the patterns of staining were inconclusive and not consistent.

CONCLUSION

In conclusion, resistance exercise stimulated a marked increase in the mRNA and protein expression of various chemotactic factors in skeletal muscle. Myofibers were not the dominant source of these factors. These findings suggest that chemotactic factors regulate remodeling/adaptation of skeletal muscle during the early phase of recovery following resistance exercise.

The effect of prior eccentric exercise on heavy-intensity cycling: the role of gender and oral contraceptives

PURPOSE

To determine if gender and/or the use of oral contraceptives alter cycling performance with exercise-induced muscle damage (EiMD).

METHODS

Nine male adults (MEN), nine normally menstruating female adults (WomenNM), and nine female adults using oral contraceptives (WomenOC) participated. Gas exchange and time to exhaustion were measured during continuous cycling performed at three distinct power outputs before (pre) and 48 h after (post) 240 maximal effort eccentric contractions of the quadriceps muscles designed to induce muscle damage (i.e., EiMD).

RESULTS

The change in muscle damage (i.e., range of motion about the knee joint and serum creatine kinase activity) from pre- compared to post-EiMD was greater in MEN and WomenOC compared to the WomenNM. Time to exhaustion decreased after EiMD in MEN (5.19 ± 4.58 min, p = 0.01) and in WomenOC (2.86 ± 2.83 min, p = 0.02) but did not change in WomenNM (0.98 ± 2.28 min, p = 0.43). Accordingly, the slow component of O2 uptake, expressed relative to time to exhaustion (i.e., % min(-1)), was greater in post- compared to pre-EiMD for MEN (p = 0.02) and the WomenOC (p = 0.03), but not for the WomenNM (p = 0.12).

CONCLUSION

The preservation of exercise tolerance during heavy-intensity cycling performed after intense eccentric exercise is improved in women compared to men. Furthermore, the preservation of exercise tolerance is exclusive to 17β-estradiol and cannot be replicated with an exogenous synthetic estrogen replacement delivered in an oral contraceptive.

Sex differences in serum CK activity but not in glomerular filtration rate after resistance exercise: is there a sex dependent renal adaptative response?

We investigated differences in sex responses in serum CK activity and renal function measured by glomerular filtration rate (GFR) after an exercise session. Twenty-two healthy and trained volunteers (11 males and 11 females) performed 17 resistance exercises with 3 × 12 repetitions in a circuit training fashion. Subjects provided blood samples prior to exercise session, and at 24, 48, and 72 h following exercise sessions for creatine kinase and creatinine. Twenty-four-hour urine samples were collected before and 72 h after the exercise. Estimate (e) GFR was obtained by using the Chronic Kidney Disease Epidemiology Collaboration equation adjusted for males and females. After the exercise session, males showed greater serum CK activity than females (p < 0.02), serum creatinine increased 31.3 % for males and 29.8 % for females, and urinary creatinine decreased on average 5.4 % for males and 0.6 % for females, with no significant differences (p > 0.05) between sex for serum and urinary creatinine. eGFR decreased significantly for males (~10 %) and females (~8 %), but also without a difference between the sexes (p > 0.05). The correlation between CK and eGFR was significant for males (r = -0.794; p = 0.003), and females (r = -0.8875; p < 0.001). A significant negative correlation between CK activity and the eGFR indice of renal function in both males and females was observed. Additionally, the renal function compromise was similar for both sexes, despite males presenting greater exercise-induced skeletal muscle damage when compared to females.

A single bout of downhill running transiently increases HOMA-IR without altering adipokine response in healthy adult women

PURPOSE

Eccentric exercise-induced muscle damage may cause marked alterations in insulin sensitivity. However, it is not entirely known whether such alterations are also related to changes in adipokine levels. The aim of this study was to investigate the effects of muscle damage due to downhill running on inflammation, insulin sensitivity and selected adipokines related to insulin regulation (adiponectin, visfatin, resistin).

METHODS

Data were collected from 12 healthy adult women. Each subject participated in two trials, 4 weeks apart. The first trial was reserved for resting measurements only (control trial), while the second trial involved a 45-min exercise (-15 % slope, ~60 % of VO2max) intervention (exercise trial). Insulin sensitivity (HOMA), creatine kinase activity (CK), delayed onset muscle soreness (DOMS), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), glucose, insulin, adiponectin, resistin, and visfatin were assessed pre-exercise and 1, 2, 3, and 4 days post-exercise and during the same time points in the control trial.

RESULTS

Analyses revealed that CK, DOMS, TNF-α, IL-6, insulin and HOMA significantly increased (p < 0.05) throughout recovery (days 1-4). Adiponectin and visfatin remained unchanged, while resistin significantly increased (p < 0.05) only 2 days post-exercise. Visfatin was negatively correlated with HOMA at days 1 and 4 of recovery.

CONCLUSION

Although muscle damage due to downhill running caused a decline of insulin sensitivity, this response was not associated with the changes in adipokine levels.

Effects of estrogen fluctuation during the menstrual cycle on the response to stretch-shortening exercise in females

The aim of this study was to investigate whether variation in estrogen levels during the menstrual cycle influences susceptibility to exercise-induced muscle damage after stretch-shortening cycle exercise. Physically active women (n = 18; age = 20.2 ± 1.7 yr) participated in this research. The subjects performed one session of 100 maximal drop jumps on day 1 or 2 of the follicular phase and another identical session on day 1 or 2 of the ovulatory phase; the order of the sessions was randomized. Quadriceps femoris muscle peak torque evoked by electrical stimulation and maximal voluntary contraction, muscle pain, and CK activity were measured before and at various times up to 72 h after exercise. It was found that the high estrogen level during the ovulatory phase might be related to an earlier return to baseline muscle strength after strenuous stretch-shortening cycle exercise in that phase compared with the follicular phase. The estrogen effect appears to be highly specific to the damaged site because the differences in most EIMD markers (CK, soreness, and low-frequency fatigue) between the two menstrual cycle phases were small.

Cold-water immersion and other forms of cryotherapy: physiological changes potentially affecting recovery from high-intensity exercise

High-intensity exercise is associated with mechanical and/or metabolic stresses that lead to reduced performance capacity of skeletal muscle, soreness and inflammation. Cold-water immersion and other forms of cryotherapy are commonly used following a high-intensity bout of exercise to speed recovery. Cryotherapy in its various forms has been used in this capacity for a number of years; however, the mechanisms underlying its recovery effects post-exercise remain elusive. The fundamental change induced by cold therapy is a reduction in tissue temperature, which subsequently exerts local effects on blood flow, cell swelling and metabolism and neural conductance velocity. Systemically, cold therapy causes core temperature reduction and cardiovascular and endocrine changes. A major hindrance to defining guidelines for best practice for the use of the various forms of cryotherapy is an incongruity between mechanistic studies investigating these physiological changes induced by cold and applied studies investigating the functional effects of cold for recovery from high-intensity exercise. When possible, studies investigating the functional recovery effects of cold therapy for recovery from exercise should concomitantly measure intramuscular temperature and relevant temperature-dependent physiological changes induced by this type of recovery strategy. This review will discuss the acute physiological changes induced by various cryotherapy modalities that may affect recovery in the hours to days (<5 days) that follow high-intensity exercise.

Changes in lymphocyte HSP70 levels in women handball players throughout 1 year of training: the role of estrogen levels

Heat shock protein 70 (HSP70) is a chaperone that maintains protein conformation during heat stress. It has recently been observed that HSP70 may be released from cells in response to increased energy demand (e.g., exercise) and/or oxidative stress. Since HSP70 levels should change in response to athletic training, we have investigated whether blood HSP70 levels in young women handball players change over a complete training season. Thirty women handball players (12-24 years old) were divided into low (≥30 pg mL(-1)) (LE) and normal (30-330 pg mL(-1)) (NE) estradiol groups. HSP70 levels in lymphocytes and plasma and blood redox parameters were evaluated over 1 year (2009), with sampling at the beginning, middle, and end of the season. We observed no changes in superoxide dismutase activity or protein carbonyl or extracellular HSP70 levels, while catalase activity increased at the middle of the season in the NE group, and the thiobarbituric acid species levels in both groups were higher at the beginning of the season than at the middle or end. The lymphocyte HSP70 content was higher at the middle and end than at the beginning of the season in the NE group and also higher in the LE group than in the NE group at the beginning of the season. These results suggest that plasma estradiol levels may play an important role in exercise training and that the intracellular HSP70 content, a biomarker for inflammation, is affected by both estradiol levels and exercise-induced oxidative stress.

Effects of Panax ginseng Supplementation on Muscle Damage and Inflammation after Uphill Treadmill Running in Humans

The purpose of this investigation was to determine whether Panax ginseng extract intake would influence exercise-induced muscle damage and inflammation responses. Eighteen male college students were randomly assigned to either an RG intake group (RG, n = 9) or a placebo group (P, n = 9). All subjects performed a high-intensity uphill treadmill running task (two rounds of 45 min at 10 km/h speed with a 15 degree uphill slope separated by 5 min of rest). The RG group ingested 20 g/day of Korean red ginseng extract (mixed with 200 ml of water) three times/day for seven days prior to performing the uphill treadmill exercise test and for four days after the treadmill test, while the P group ingested 200 ml of water containing Agastachis Herba on the same schedule. Plasma creatine kinase activity (CK) and interlukin-6 (IL-6) levels were measured at pre-exercise and 24, 48, 72, and 96 h post-exercise; the IL-6 level was also measured at 1 and 2 h post-exercise. To evaluate insulin sensitivity, the oral glucose tolerance test (OGTT) was performed 24 h post-exercise. Plasma CK level in RG was significantly lower than that in P 72 h post-exercise (p < 0.05), and IL-6 level was significantly decreased in RG during the 2 h and 3 h recovery period compared to that of P (p < 0.05). Plasma glucose and insulin responses in RG were significantly reduced compared to those of P (p < 0.05). The results of this study suggest that RG supplementation could reduce exercise-induced muscle damage and inflammatory responses, resulting in improvements in insulin sensitivity.

The role of androgens and estrogens on healthy aging and longevity

Aging is associated with a loss of sex hormone in both men (andropause) and women (menopause). In men, reductions in testosterone can trigger declines in muscle mass, bone mass, and in physical function. In women, the impact of the loss of sex hormones, such as estradiol, on bone is well elucidated, but evidence is limited on whether the loss of estradiol negatively affects muscle mass and physical function. However, deficiencies in multiple anabolic hormones have been shown to predict health status and longevity in older persons. Thus, consideration should be given as to whether targeted hormone replacement therapies may prove effective at treating clinical conditions, such as age-related sarcopenia, cancer cachexia, and/or acute or chronic illnesses. If initiated carefully in the appropriate clinical population, hormone replacement therapies in men and women may prevent and reverse muscle and bone loss and functional declines and perhaps promote healthy aging and longevity.

Creatine-kinase- and exercise-related muscle damage implications for muscle performance and recovery

The appearance of creatine kinase (CK) in blood has been generally considered to be an indirect marker of muscle damage, particularly for diagnosis of medical conditions such as myocardial infarction, muscular dystrophy, and cerebral diseases. However, there is controversy in the literature concerning its validity in reflecting muscle damage as a consequence of level and intensity of physical exercise. Nonmodifiable factors, for example, ethnicity, age, and gender, can also affect enzyme tissue activity and subsequent CK serum levels. The extent of effect suggests that acceptable upper limits of normal CK levels may need to be reset to recognise the impact of these factors. There is a need for standardisation of protocols and stronger guidelines which would facilitate greater scientific integrity. The purpose of this paper is to examine current evidence and opinion relating to the release of CK from skeletal muscle in response to physical activity and examine if elevated concentrations are a health concern.

Skeletal muscle gender dimorphism from proteomics

Gross contraction in skeletal muscle is primarily determined by a relatively small number of contractile proteins, however this tissue is also remarkably adaptable to environmental factors such as hypertrophy by resistance exercise and atrophy by disuse. It thereby exhibits remodeling and adaptations to stressors (heat, ischemia, heavy metals, etc.). Damage can occur to muscle by a muscle exerting force while lengthening, the so-called eccentric contraction. The contractile proteins can be damaged in such exertions and need to be repaired, degraded and/or resynthesized; these functions are not part of the contractile proteins, but of other much less abundant proteins in the cell. To determine what subset of proteins is involved in the amelioration of this type of damage, a global proteome must be established prior to exercise and then followed subsequent to the exercise to determine the differential protein expression and thereby highlight candidate proteins in the adaptations to damage and its repair. Furthermore, most studies of skeletal muscle have been conducted on the male of the species and hence may not be representative of female muscle. In this article we present a method for extracting proteins reproducibly from male and female muscles, and separating them by two-dimensional gel electrophoresis followed by high resolution digital imaging. This provides a protocol for spots (and subsequently identified proteins) that show a statistically significant (p < 0.05) two-fold increase or decrease, appear or disappear from the control state. These are then excised, digested with trypsin and separated by high-pressure liquid chromatography coupled to a mass spectrometer (LC/MS) for protein identification (LC/MS/MS). This methodology (Figure 1) can be used on many tissues with little to no modification (liver, brain, heart etc.).

17β-estradiol attenuates exercise-induced neutrophil infiltration in men

17β-estradiol (E2) attenuates exercise-induced muscle damage and inflammation in some models. Eighteen men completed 150 eccentric contractions after random assignment to placebo (Control group) or E2 supplementation (Experimental group). Muscle biopsies and blood samples were collected at baseline, following 8-day supplementation and 3 h and 48 h after exercise. Blood samples were analyzed for sex hormone concentration, creatine kinase (CK) activity and total antioxidant capacity. The mRNA content of genes involved in lipid and cholesterol homeostasis [forkhead box O1 (FOXO1), caveolin 1, and sterol regulatory element binding protein-2 (SREBP2)] and antioxidant defense (SOD1 and -2) were measured by RT-PCR. Immunohistochemistry was used to quantify muscle neutrophil (myeloperoxidase) and macrophage (CD68) content. Serum E2 concentration increased 2.5-fold with supplementation ( P < 0.001), attenuating neutrophil infiltration at 3 h ( P < 0.05) and 48 h ( P < 0.001), and the induction of SOD1 at 48 h ( P = 0.02). Macrophage density at 48 h ( P < 0.05) and SOD2 mRNA at 3 h ( P = 0.01) increased but were not affected by E2. Serum CK activity was higher at 48 h for both groups ( P < 0.05). FOXO1, caveolin 1 and SREBP2 expression were 2.8-fold ( P < 0.05), 1.4-fold ( P < 0.05), and 1.5-fold ( P < 0.001) and higher at 3 h after exercise with no effect of E2. This suggests that E2 attenuates neutrophil infiltration; however, the mechanism does not appear to be lesser oxidative stress or membrane damage and may indicate lesser neutrophil/endothelial interaction.

Hindlimb skeletal muscle function in myostatin-deficient mice

Absence of functional myostatin (MSTN) during fetal development results in adult skeletal muscle hypertrophy and hyperplasia. To more fully characterize MSTN loss in hindlimb muscles, the morphology and contractile function of the soleus, plantaris, gastrocnemius, tibialis anterior, and quadriceps muscles in male and female null (Mstn(-/-)), heterozygous (Mstn(+/-)), and wild-type (Mstn(+/+)) mice were investigated. Muscle weights of Mstn(-/-) mice were greater than those of Mstn(+/+) and Mstn(+/-) mice. Fiber cross-sectional area (CSA) was increased in female Mstn(-/-) soleus and gastrocnemius muscles and in the quadriceps of male Mstn(-/-) mice; peak tetanic force in Mstn(-/-) mice did not parallel the increased muscle weight or CSA. Male Mstn(-/-) muscle exhibited moderate degeneration. Visible pathology in male mice and decreased contractile strength relative to increased muscle weight suggest MSTN loss results in muscle impairment, which is dose-, sex-, and muscle-dependent.

Sex differences in intracellular Ca2+ accumulation following eccentric contractions of rat skeletal muscle in vivo

It is commonly believed that estrogen and sex influences play significant effects in skeletal muscle damage following eccentric exercise. The mechanistic bases for this sex-specific phenomenon remain to be resolved. The muscle damage has been linked to loss of Ca2+ homeostasis and resultant intramyocyte Ca2+ ([Ca2+]i) accumulation; therefore, we tested the hypothesis that the greater eccentric exercise-induced muscle damage in males would be associated with more pronounced [Ca2+]i accumulation. The intact spinotrapezius muscle of adult Wistar rats [male, female, and ovariectomized (OVX)—to investigate the effects of estrogen] was exteriorized. Tetanic eccentric contractions (100 Hz, 700-ms duration, 20 contractions/min for a total of 10 sets of 50 contractions) were elicited by electrical stimulation during synchronized muscle stretch of 10% resting muscle length. The fluorescence ratio (F340/F380 nm) was determined from images captured following each set of contractions, and fura-2 AM was used to estimate [Ca2+]i and changes thereof. Following eccentric contractions, [Ca2+]i increased significantly in male (42.8 ± 5.3%, P < 0.01) but not in female (9.4 ± 3.5%) rats. OVX evidenced an intermediate response (17.0 ± 1.2%) that remained significantly reduced compared with males. These results demonstrate that females maintain [Ca2+]i homeostasis following novel eccentric contractions, whereas males do not, which is consistent with a role for elevated [Ca2+]i in eccentric exercise-induced muscle damage. The presence of normal estrogen levels is not obligatory for the difference between the sexes.

Whey protein isolate attenuates strength decline after eccentrically-induced muscle damage in healthy individuals

Background

We examined the effects of short-term consumption of whey protein isolate on muscle proteins and force recovery after eccentrically-induced muscle damage in healthy individuals.

Methods

Seventeen untrained male participants (23 ± 5 yr, 180 ± 6 cm, 80 ± 11 kg) were randomly separated into two supplement groups: i) whey protein isolate (WPH; n = 9); or ii) carbohydrate (CHO; n = 8). Participants consumed 1.5 g/kg.bw/day supplement (~30 g consumed immediately, and then once with breakfast, lunch, in the afternoon and after the evening meal) for a period of 14 days following a unilateral eccentric contraction-based resistance exercise session, consisting of 4 sets of 10 repetitions at 120% of maximum voluntary contraction on the leg press, leg extension and leg flexion exercise machine. Plasma creatine kinase and lactate dehydrogenase (LDH) levels were assessed as blood markers of muscle damage. Muscle strength was examined by voluntary isokinetic knee extension using a Cybex dynamometer. Data were analyzed using repeated measures ANOVA with an alpha of 0.05.

Results

Isometric knee extension strength was significantly higher following WPH supplementation 3 (P < 0.05) and 7 (P < 0.01) days into recovery from exercise-induced muscle damage compared to CHO supplementation. In addition, strong tendencies for higher isokinetic forces (extension and flexion) were observed during the recovery period following WPH supplementation, with knee extension strength being significantly greater (P < 0.05) after 7 days recovery. Plasma LDH levels tended to be lower (P = 0.06) in the WPH supplemented group during recovery.

Conclusions

The major finding of this investigation was that whey protein isolate supplementation attenuated the impairment in isometric and isokinetic muscle forces during recovery from exercise-induced muscle injury.

Gender dimorphism in the exercise-naïve murine skeletal muscle proteome

Skeletal muscle is a plastic tissue with known gender dimorphism, especially at the metabolic level. A proteomic comparison of male and female murine biceps brachii was undertaken, resolving an average of 600 protein spots of MW 15-150 kDa and pI 5-8. Twenty-six unique full-length proteins spanning 11 KOG groups demonstrated statistically significant (p<0.05) abundance differences between genders; the majority of these proteins have metabolic functions. Identified glycolytic enzymes demonstrated decreased abundance in females, while abundance differences in identified oxidative phosphorylation enzymes were specific to the proteins rather than to the functional group as a whole. Certain cytoskeletal and stress proteins showed specific expression differences, and all three phosphorylation states of creatine kinase showed significant decreased abundance in females. Expression differences were significant but many were subtle (< or = 2-fold), and known hormonally-regulated proteins were not identified. We conclude that while gender dimorphism is present in non-exercised murine skeletal muscle, the proteome comparison of male and female biceps brachii in exercise-naive mice indicates subtle differences rather than a large or obviously hormonal dimorphism.

Impact of serum estradiol on postprandial lipemia, oxidative stress, and inflammation across a single menstrual cycle

BACKGROUND

An abrupt rise in circulating lipids, oxidative stress, and inflammatory biomarkers is a common finding after ingestion of a high-fat meal. Estradiol, typically provided via hormone replacement therapy to postmenopausal women, has been reported to possess lipidemic, antioxidant, and antiinflammatory properties, all of which may minimize postprandial oxidative stress.

OBJECTIVE

The purpose of this study was to compare the postprandial triglyceride (TG), oxidative stress, and inflammatory responses after a lipid meal in menstruating women during the early follicular (days 1-3) and preovulatory (day 14) phases of the menstrual cycle.

METHODS

Healthy normolipidemic women (fasting blood TG, <200 mg/dL) with regular menstrual cycles reported to the Cardiorespiratory/Metabolic Laboratory at the University of Memphis, Memphis, Tennessee (October-December 2008) and consumed an identical lipid meal (heavy whipping cream and water) on 2 separate days during the menstrual cycle. Blood samples were collected premeal and 1, 2, 4, and 6 hours postmeal, then assayed for TG, malondialdehyde (MDA), hydrogen peroxide, Trolox equivalent antioxidant capacity (TEAL), nitrate/nitrite, and C-reactive protein (CRP). The AUC was calculated for each variable, and a 2 (menstrual cycle phase) x 5 (time) ANOVA with Tukey post hoc testing was also conducted. Estradiol concentration was measured in premeal samples for verification of cycle phase.

RESULTS

Ten women (mean [SD] age, 29 [11] years; 8 white, 2 black; body mass index, 22 [3] kg/m(2)) participated in the study. Despite a higher serum estradiol concentration on day 14 (113 [56] pg/mL) compared with the early follicular phase (61 [34] pg/mL), the TG, oxidative stress, and inflammatory AUC responses to feeding were not significantly different. TG (P = 0.03), MDA (P = 0.02), and hydrogen peroxide (P < 0.001) were significantly increased in response to feeding (time effect), whereas nitrate/nitrite was decreased (P = 0.01). TEAC and CRP were not significantly affected.

CONCLUSIONS

These data indicate that estradiol, at the concentrations noted in the present study, had no significant effect on postprandial TG or biomarkers of oxidative stress or inflammation in a sample of young, healthy women. It is possible that a greater divergence in circulating estradiol may be needed for significant differences to be detected, as may be the case with chronic hormone replacement therapy in postmenopausal women.

The influence of estrogen on skeletal muscle: sex matters

As women enter menopause, the concentration of estrogen and other female hormones declines. This hormonal decrease has been associated with a number of negative outcomes, including a greater incidence of injury as well as a delay in recovery from these injuries. Over the past two decades, our understanding of the protective effects of estrogen against various types of injury and disease states has grown immensely. In skeletal muscle, studies with animals have demonstrated that sex and estrogen may potentially influence muscle contractile properties and attenuate indices of post-exercise muscle damage, including the release of creatine kinase into the bloodstream and activity of the intramuscular lysosomal acid hydrolase, beta-glucuronidase. Furthermore, numerous studies have revealed an estrogen-mediated attenuation of infiltration of inflammatory cells such as neutrophils and macrophages into the skeletal muscles of rats following exercise or injury. Estrogen has also been shown to play a significant role in stimulating muscle repair and regenerative processes, including the activation and proliferation of satellite cells. Although the mechanisms by which estrogen exerts its influence upon indices of skeletal muscle damage, inflammation and repair have not been fully elucidated, it is thought that estrogen may potentially exert its protective effects by: (i) acting as an antioxidant, thus limiting oxidative damage; (ii) acting as a membrane stabilizer by intercalating within membrane phospholipids; and (iii) binding to estrogen receptors, thus governing the regulation of a number of downstream genes and molecular targets. In contrast to animal studies, studies with humans have not as clearly delineated an effect of estrogen on muscle contractile function or on indices of post-exercise muscle damage and inflammation. These inconsistencies have been attributed to a number of factors, including age and fitness level of subjects, the type and intensity of exercise protocols, and a focus on sex differences that typically involve factors and hormones in addition to estrogen. In recent years, hormone replacement therapy (HRT) or estrogen combined with exercise have been proposed as potentially therapeutic agents for postmenopausal women, as these agents may potentially limit muscle damage and inflammation and stimulate repair in this population. While the benefits and potential health risks of long-term HRT use have been widely debated, controlled studies using short-term HRT or other estrogen agonists may provide future new and valuable insights into understanding the effects of estrogen on skeletal muscle, and greatly benefit the aging female population. Recent studies with older females have begun to demonstrate their benefits.

Oestradiol and SERM treatments influence oestrogen receptor coregulator gene expression in human skeletal muscle cells

AIM

Oestrogen receptors (ER) are present in human skeletal muscle (hSkM) cells; however, the function of the receptor is currently unknown. We investigated the influence of oestradiol and selective ER modulators [tamoxifen (TAM), raloxifene (RAL)] on ER coregulator mRNA expression in hSkM.

METHODS

Human skeletal muscle cells were treated with 10 nm oestradiol, 5 microm TAM and 10 microm RAL over a 24-h period. Following the treatment period, mRNA expression was quantified using real-time PCR to detect changes in ER-alpha, ER-beta, steroid receptor coactivator (SRC), silencing mediator for retinoid and thyroid hormone receptors (SMRT), MyoD, GLUT4 and c-fos.

RESULTS

ER-alpha mRNA expression increased with all three drug treatments (P < 0.05) while there was no change in mRNA expression of ER-beta in hSkM cells. mRNA expression of SRC increased and SMRT decreased with oestradiol, TAM and RAL in hSkM cells (P < 0.05). Importantly, mRNA expression of MyoD increased with oestradiol and decreased with TAM and RAL in hSkM cells (P < 0.05). mRNA expression of GLUT4 increased with oestradiol and RAL and decreased with TAM in hSkM cells (P < 0.05).

CONCLUSIONS

These findings are novel in that they provide the first evidence that oestradiol and selective ER modulators influence ER-alpha function in hSkM cells. This demonstrates the importance of the ER and alterations in its coregulators, to potentially prevent sarcopenia and promote muscle growth in postmenopausal women using these forms of hormone replacement therapy.

Hormone therapy attenuates exercise-induced skeletal muscle damage in postmenopausal women

Hormone therapy (HT) is a potential treatment to relieve symptoms of menopause and prevent the onset of disease such as osteoporosis in postmenopausal women. We evaluated changes in markers of exercise-induced skeletal muscle damage and inflammation [serum creatine kinase (CK), serum lactate dehydrogenase (LDH), and skeletal muscle mRNA expression of IL-6, IL-8, IL-15, and TNF-alpha] in postmenopausal women after a high-intensity resistance exercise bout. Fourteen postmenopausal women were divided into two groups: women not using HT (control; n = 6, 59 +/- 4 yr, 63 +/- 17 kg) and women using traditional HT (HT; n = 8, 59 +/- 4 yr, 89 +/- 24 kg). Both groups performed 10 sets of 10 maximal eccentric repetitions of single-leg extension on the Cybex dynamometer at 60 degrees /s with 20-s rest periods between sets. Muscle biopsies of the vastus lateralis were obtained from the exercised leg at baseline and 4 h after the exercise bout. Gene expression was determined by RT-PCR for IL-6, IL-8, IL-15, and TNF-alpha. Blood draws were performed at baseline and 3 days after exercise to measure CK and LDH. Independent t-tests were performed to test group differences (control vs. HT). A probability level of P <or= 0.05 was used to determine statistical significance. We observed significantly greater changes in mRNA expression of IL-6, IL-8, IL-15, and TNF-alpha (P <or= 0.01) in the control group compared with the HT group after the exercise bout. CK and LDH levels were significantly greater after exercise (P <or= 0.01) in the control group. Postmenopausal women not using HT experienced greater muscle damage after maximal eccentric exercise, indicating a possible protective effect of HT against exercise-induced skeletal muscle damage.

Creatine supplementation enhances muscle force recovery after eccentrically-induced muscle damage in healthy individuals

Background

Eccentric exercise-induced damage leads to reductions in muscle force, increased soreness, and impaired muscle function. Creatine monohydrate's (Cr) ergogenic potential is well established; however few studies have directly examined the effects of Cr supplementation on recovery after damage. We examined the effects of Cr supplementation on muscle proteins and force recovery after eccentrically-induced muscle damage in healthy individuals.

Methods

Fourteen untrained male participants (22.1 ± 2.3 yrs, 173 ± 7.7 cm, 76.2 ± 9.3 kg) were randomly separated into 2 supplement groups: i) Cr and carbohydrate (Cr-CHO; n = 7); or ii) carbohydrate (CHO; n = 7). Participants consumed their supplement for a period of 5 days prior to, and 14 days following a resistance exercise session. Participants performed 4 sets of 10 eccentric-only repetitions at 120% of their maximum concentric 1-RM on the leg press, leg extension and leg flexion exercise machine. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activity were assessed as relevant blood markers of muscle damage. Muscle strength was examined by voluntary isokinetic knee extension using a Cybex dynamometer. Data were analyzed using repeated measures ANOVA with an alpha of 0.05.

Results

The Cr-supplemented group had significantly greater isokinetic (10% higher) and isometric (21% higher) knee extension strength during recovery from exercise-induced muscle damage. Furthermore, plasma CK activity was significantly lower (by an average of 84%) after 48 hrs (P < 0.01), 72 hrs (P < 0.001), 96 hrs (P < 0.0001), and 7 days (P < 0.001) recovery in the Cr-supplemented group.

Conclusion

The major finding of this investigation was a significant improvement in the rate of recovery of knee extensor muscle function after Cr supplementation following injury.

Emerging peripheral receptor targets for deep-tissue craniofacial pain therapies

While effective therapies are available for some types of craniofacial pain, treatments for deep-tissue craniofacial pain such as temporomandibular disorders are less efficacious. Several ion channels and receptors which are prominent in craniofacial nociceptive mechanisms have been identified on trigeminal primary afferent neurons. Many of these receptors and channels exhibit unusual distributions compared with extracranial regions. For example, expression of the ATP receptor P2X(3) is strongly implicated in nociception and is more abundant on trigeminal primary afferent neurons than analogous extracranial neurons, making them potentially productive targets specifically for craniofacial pain therapies. The initial part of this review therefore focuses on P2X(3) as a potential therapeutic target to treat deep-tissue craniofacial pain. In the trigeminal ganglion, P2X(3) receptors are often co-expressed with the nociceptive neuropeptides CGRP and SP. Therefore, we discuss the role of CGRP and SP in deep-tissue craniofacial pain and suggest that neuropeptide antagonists, which have shown promise for the treatment of migraine, may have wider therapeutic potential, including the treatment of deep-tissue craniofacial pain. P2X(3), TRPV1, and ASIC3 are often co-expressed in trigeminal neurons, implying the formation of functional complexes that allow craniofacial nociceptive neurons to respond synergistically to altered ATP and pH in pain. Future therapeutics for craniofacial pain thus might be more efficacious if targeted at combinations of P2X(3), CGRP, TRPV1, and ASIC3.

[Body mass regulation by estrogen and physical activity]

Female steroid hormones deficiency leads to a significant increase in body mass, but the possible central and peripheral mechanisms involved in increased food ingestion and fat accumulation in this situation are still unknown. In animal models, the specific lack of estrogen or its action produce progressive body mass gain, clearly demonstrating the possible role of this hormone in overweight after menopause. Obesity and overweight correspond to a relevant human health problem that can lead to premature death. Therefore unraveling the mechanisms underlying body mass gain is of great relevance, as well as the development of strategies to prevent its establishment. Energy balance regulation is associated with the control of body mass, and physical exercise is an important modulator of this homeostatic parameter. However, the influence of physical exercise in mass gain development during estrogen deficiency is controversial and depends on the exercise protocol used. In this study, we intend to review the data on the effects of estrogen deficiency on body mass gain in humans and animal models.

Effect of exercise on oxidative stress biomarkers

Acute bouts of aerobic and anaerobic exercise can induce a state of oxidative stress, as indicated by an increase in oxidized molecules in a variety of tissues and body fluids. The extent of oxidation is dependent on the exercise mode, intensity, and duration, and is specifically related to the degree of oxidant production. Findings of increased oxidative stress have been reported for both healthy and diseased subjects following single bouts of exercise. While acute exercise has the ability to induce an oxidative stress, this same exercise stimulus appears necessary to allow for an upregulation in endogenous antioxidant defenses. This chapter presents a summary of exercise-induced oxidative stress.

The effect of muscle-damaging exercise on blood and skeletal muscle oxidative stress: magnitude and time-course considerations

The aim of this article is to present the effects of acute muscle-damaging exercise on oxidative stress/damage of animal and human tissues using a quantitative approach and focusing on the time-course of exercise effects. The reviewed studies employed eccentric contractions on a dynamometer or downhill running. The statistical power of each study to detect a 20% or 40% post-exercise change compared with pre-exercise value in each oxidative stress/damage biomarker was calculated. Muscle-damaging exercise can increase free radical levels and augment oxidation of lipids, proteins, glutathione and possibly DNA in the blood. In contrast, the effect of muscle-damaging exercise on concentration of antioxidants in the blood, except for glutathione, was little. Muscle-damaging exercise induces oxidative stress/damage in skeletal muscle, even though this is not fully supported by the original statistical analysis of some studies. In contrast, muscle-damaging exercise does not appear to affect--at least to similar extent as the oxidative stress/damage markers--the levels of antioxidants in skeletal muscle. Based on the rather limited data available, the oxidative stress response of skeletal muscle to exercise was generally independent of muscle fibre type. Most of the changes in oxidative stress/damage appeared and were sustained for days after muscle-damaging exercise. The major part of the delayed oxidative stress/damage production that follows muscle-damaging exercise probably comes from phagocytic cells that are activated and recruited to the site of the initial damage. A point that emerged and potentially explains much of the lack of consensus among studies is the low statistical power of many of them. In summary, muscle-damaging exercise can increase oxidative stress/damage in blood and skeletal muscle of rats and humans that may persist for and/or appear several days after exercise.

The prevention and treatment of exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) can be caused by novel or unaccustomed exercise and results in a temporary decrease in muscle force production, a rise in passive tension, increased muscle soreness and swelling, and an increase in intramuscular proteins in blood. Consequently, EIMD can have a profound effect on the ability to perform subsequent bouts of exercise and therefore adhere to an exercise training programme. A variety of interventions have been used prophylactically and/or therapeutically in an attempt to reduce the negative effects associated with EIMD. This article focuses on some of the most commonly used strategies, including nutritional and pharmacological strategies, electrical and manual therapies and exercise. Long-term supplementation with antioxidants or beta-hydroxy-beta-methylbutyrate appears to provide a prophylactic effect in reducing EIMD, as does the ingestion of protein before and following exercise. Although the administration of high-dose NSAIDs may reduce EIMD and muscle soreness, it also attenuates the adaptive processes and should therefore not be prescribed for long-term treatment of EIMD. Whilst there is some evidence that stretching and massage may reduce muscle soreness, there is little evidence indicating any performance benefits. Electrical therapies and cryotherapy offer limited effect in the treatment of EIMD; however, inconsistencies in the dose and frequency of these and other interventions may account for the lack of consensus regarding their efficacy. Both as a cause and a consequence of this, there are very few evidence-based guidelines for the application of many of these interventions. Conversely, there is unequivocal evidence that prior bouts of eccentric exercise provide a protective effect against subsequent bouts of potentially damaging exercise. Further research is warranted to elucidate the most appropriate dose and frequency of interventions to attenuate EIMD and if these interventions attenuate the adaptation process. This will both clarify the efficacy of such strategies and provide guidelines for evidence-based practice.

Effects of step exercise on muscle damage and muscle Ca2+ content in men and women

Eccentric exercise often produces severe muscle damage, whereas concentric exercise of a similar load elicits a minor degree of muscle damage. The cellular events initiating muscle damage are thought to include an increase in cytosolic Ca. It was hypothesized that eccentric muscle activity in humans would lead to a larger degree of cell damage and increased intracellular Ca accumulation in skeletal muscle than concentric activity would. Furthermore, possible differences between men and women in muscle damage were investigated following step exercise. Thirty-three healthy subjects (18 men and 15 women) participated in a 30-minute step exercise protocol involving concentric contractions with 1 leg and eccentric contractions with the other leg. Muscle Ca content, maximal voluntary contraction (MVC), and muscle enzymes in the plasma were measured. In a subgroup of the subjects, T2 relaxation time was measured by magnetic resonance imaging. No significant changes were found in muscle Ca content in vastus lateralis biopsy specimens in women or in men. Following step exercise, MVC decreased in both legs of both genders. The women had a significantly larger strength decrease in the eccentric leg than the men had on postexercise day 2 (p < 0.01). Plasma creatine kinase increased following step exercise, with a sevenfold higher response in women than in men on day 3 (p < 0.001). The women, but not the men, had an increase in T2 relaxation time in the eccentrically working adductor magnus muscle, peaking on day 3 (75%) (p < 0.001). In conclusion, step exercise does not lead to Ca accumulation in the vastus lateralis but does induce muscle damage preferentially in the eccentrically working muscles, considerably more in women than in men. This indicates that gender-specific step training programs may be warranted to avoid excessive muscle damage.

Gender comparisons of exercise-induced oxidative stress: influence of antioxidant supplementation

The purpose of this study was to determine the influence of gender and antioxidant supplementation on exercise-induced oxidative stress. Twenty-five men and 23 women ran for 30 min at 80% VO2 max, once before and once after 2 weeks of supplementation, and again after a 1-week wash-out period. Subjects were randomly assigned to either placebo (P), antioxidant (A: 400 IU vitamin E+1 g vitamin C), or a fruit and vegetable powder (FV) treatment. Blood was obtained at rest and immediately after exercise. Before supplementation, women had higher resting reduced glutathione, total glutathione, and plasma vitamin E compared with men. With both A and FV supplementations, plasma vitamin E gender differences disappeared. Protein carbonyls, oxidized glutathione, and malondialdehyde all increased similarly for both genders in response to exercise. Both A and FV attenuated the reduced glutathione decrease and the oxidized glutathione and protein carbonyls increase compared with P, with no gender differences. 8-hydroxydeoxyguanosine was lower with treatment A compared with FV and P only for men. Plasma vitamin C increased 39% (A) and 21% (FV) compared with P. These data indicate that women have higher resting antioxidant levels than men. Markers of oxidative stress increased similarly in both genders in response to exercise of similar intensity and duration. Two weeks of antioxidant supplementation can attenuate exercise-induced oxidative stress equally in both genders.

Soleus muscle force following downhill running in ovariectomized rats treated with estrogen

The ovariectomized (OVX) rat model was used to investigate the effects of estrogen treatment on soleus muscle functionality in situ following muscle injury induced by downhill running. Fifty immature, 24- to 26-d-old, OVX rats were randomly assigned to 5 separate experimental groups: sedentary controls (OVX-Sed), placebo-treated and studied immediately after exercise (OVX-Pb0), placebo-treated and studied 72 h after exercise (OVX-Pb72), estradiol-treated and studied immediately after exercise (OVX-Ed0), and estradiol-treated and studied 72 h after exercise (OVX-Ed72). At the age of 9 weeks, under ketamine and xylazine anesthesia i.p., the rats were subcutaneously implanted with either placebo or 17beta-estradiol-impregnated pellets (0.05 mg/pellet, 3 week release). Treatment with 17beta-estradiol increased the estradiol plasma levels in OVX animals to those normally seen during the proestrous cycle of normal animals. Three weeks after the implantation the rats were subjected to a 90 min intermittent downhill running protocol. Our results indicate that the exercise protocol used in the study induced injury in the soleus muscle, as it was detected by the significant reduction in unfused (stimulation at 10, 20, and 40 Hz) and maximal (Po) tetanic force, as well as the decreased ability of the soleus muscle to maintain tension (stimulation at 40 Hz for 3 min) in OVX-Pb0 and OVX-Pb72 placebo-treated animals subjected to downhill running (injured muscles) as compared with OVX-Sed control rats (uninjured muscle). Estradiol replacement in OVX rats partially protected the soleus muscle from the injury normally induced by downhill running. As compared with the OVX-Pb0 and OVX-Pb72 placebo-treated groups, the soleus muscles of OVX-Ed0 and OVX-Ed72 estradiol-treated rats were capable of producing significantly greater unfused tetanic force and had an increased ability to maintain tension after fatigue. However, estrogen at the dose administered did not prevent the decrease in maximal tetanic force. We postulate that the protective effect of estrogens on muscle strength may be related to the ability of estrogen hormones to attenuate the E--C coupling failure and (or) the disorganization of the contractile apparatus associated with eccentric exercise through a mechanism or mechanisms yet to be fully understood.

Ovarian hormone status and skeletal muscle inflammation during recovery from disuse in rats

Resumption of normal muscle loading after a period of disuse initiates cellular processes related to mass accretion. The renewed loading also induces a significant amount of muscle damage and subsequent inflammation. Ovarian hormone depletion delays atrophied myofibre mass recovery. Ovarian hormones are also global regulators of immune system function. The purpose of this study was to determine whether ovarian hormone depletion-induced deficits in myofibre regrowth after disuse atrophy are related to the induction of muscle damage and the associated inflammatory response. We hypothesized that soleus muscle immune cell infiltration and inflammatory gene expression would be both accentuated and prolonged in ovarian hormone-depleted rats during the first week of recovery from disuse atrophy. Intact and ovariectomized (OVX) female rats were subjected to hindlimb suspension for 10 days and then returned to normal ambulation for a recovery period, the rats were killed and the soleus muscle removed for analysis. Although reloading increased both circulating creatine kinase and myofibre membrane disruption, there was no effect of ovarian hormones on these processes during recovery. Muscle neutrophil concentration was increased above baseline regardless of hormone status at days 1 and 3 of recovery; however, this increase was 43% greater at day 3 in the OVX group. Muscle ED1+ and ED2+ macrophage concentrations were increased during recovery in both groups. However, macropage concentrations remained elevated at day 7 of recovery in the OVX group, whereas they returned to control levels in the intact group. Cyclo-oxygenase-2, interleukin-6 and interleukin-1beta muscle mRNA expression increased similarly during recovery, regardless of ovarian hormone status. These results demonstrate that the initial myofibre damage and inflammatory gene expression induced during muscle recovery from disuse atrophy are independent of ovarian hormone status.

Effects of sensory-level high-volt pulsed electrical current ondelayed-onset muscle soreness

Ten healthy males and ten healthy females aged 21.5 +/- 3.2 years (mean +/- s) participated in the study, which was designed to evaluate the effectiveness of sensory level-high volt pulsed electrical current (HVPC) on delayed-onset muscle soreness (DOMS). Arm discomfort, elbow extension range of motion and isometric elbow flexion strength were obtained as baseline measurements. Delayed-onset muscle soreness was induced in the participants' dominant or non-dominant arm using two sets of 20 maximal eccentric elbow flexion contractions. After the induction of DOMS, the participants were randomly divided into an experimental condition (HVPC) or a placebo condition. The experimental condition consisted of 20 min of HVPC immediately after the induction of DOMS, and 20 min every 24 h for three consecutive days thereafter. The participants in the placebo condition received an intervention similar in design; however, no electrical current was administered. Baseline measurements were reevaluated at 24, 48, 72 and 96 h after the induction of DOMS. Three weeks later, the participants returned and the protocol was repeated on the contralateral limb, using the opposite intervention (HVPC or placebo). Repeated-measures analysis of variance revealed a significant increase in overall arm discomfort, decrease in elbow extension and decrease in isometric strength for both conditions over time. No significant main effect of treatment, or time-by-treatment interaction, was found for the HVPC condition when compared with the placebo condition for any variable. Sensory-level HVPC, as utilized in our application, was ineffective in reducing the measured variables associated with DOMS.

Variability in muscle damage after eccentric exercise and the repeated bout effect

The first purpose of this study was to determine a possible explanation for the variability in the response to eccentric exercise by having participants repeat the same exercise 1 year apart. The second purpose was to examine whether initial injury in response to eccentric exercise was associated with the extent of the repeated bout effect (RBE). Male students performed 30 eccentric contractions (ECC) of the elbow flexors using a dumbbell set at 80% of the pre-exercise maximal isometric force (MIF). Participants were then classified into low (LR; n=6), medium (MR; n=6), high (HR; n=5), and higher (HrR; n=7) based on the increase in blood creatine kinase (CK) activity. A year later, participants repeated this exercise (ECC30). Four days after ECC30, participants performed 70 eccentric contractions (ECC70). Range of motion, MFI upper arm circumference, soreness, and blood CK activity were measured before and up to 9 days after each bout. The change in the criterion measures following ECC and ECC30 were similar for each group. There were no further changes in all parameters after ECC70 for MR, HR, and HrR, although there was a small increase in CK after ECC70 for LR. LR showed a smaller RBE after ECC70 compared with the other groups. It is concluded that participants who exercised 1 year apart showed remarkably similar responses between the bouts. The extent of the RBE following the second bout for the LR group is less for participants who demonstrate the least evidence of muscle damage after a first exercise bout.