Bout Of Eccentric Exercise Research Articles

Effects of eccentric exercise on toll-like receptor 4 signaling pathway in peripheral blood mononuclear cells

This study aimed to investigate the response of the toll-like receptor 4 (TLR4) signaling pathway to an acute bout of eccentric exercise, and to assess whether eccentric training attenuated the effects induced by acute eccentric exercise. Twenty men (22.4 ± 0.5 yr) were divided into a control group (CG, n = 8) and a training group (TG, n = 12). Both groups performed two acute eccentric bouts on a squat machine in a 9-wk interval. During this time, TG followed a 6-wk eccentric training program (3 session/wk; 3-5 sets of 10 repetitions with loads ranging between the 40 and 50% of maximal isometric voluntary contraction). CD14, TLR4, and TNF-α mRNA levels, and CD14, TLR4, myeloid differentiation factor 88, tumor necrosis factor receptor-associated factor 6, TIR-domain-containing adapter-inducing interferon-β, phospho-IκB kinases, phospho-IκB, phospho-ERK-1/2, and TNF-α protein concentration were measured in peripheral blood mononuclear cells, before, immediately, and 2 h after each eccentric bout. The first acute eccentric bout triggered a proinflammatory response mediated by an upregulation of all of the factors measured within the TLR4 signaling pathway. Following the training period and after the second acute bout, CG showed a similar proinflammatory response than that seen after the first bout. However, the eccentric training intervention decreased significantly the protein concentration of all factors analyzed in TG compared with results obtained after the first bout. These results suggest that the TLR4-signaling pathway plays a critical role in the proinflammatory response seen after acute eccentric exercise. This response was attenuated after an eccentric training program through myeloid differentiation factor 88-dependent and -independent pathways.

No adverse effects of statins on muscle function and health‐related parameters in the elderly: An exercise study

The aim of the present study was to investigate the effects of a repeated bout of eccentric exercise on health-related parameters and muscle performance on subjects undergoing atorvastatin therapy. Twenty-eight elderly men participated in the investigation and were assigned either in a control (n = 14) or in a statin therapy group (n = 14). All participants performed two isokinetic eccentric exercise bouts separated by 3 weeks. Muscle damage indices, resting energy expenditure, substrate metabolism, lipid and lipoprotein profile, as well as insulin sensitivity, were evaluated before and after eccentric. No differences in muscle function were observed between the two groups either at rest or after exercise. Eccentric exercise increased resting energy expenditure, increased fat oxidation, improved lipid profile, and increased insulin resistance 2 days after both eccentric exercise bouts. However, these changes appeared to lesser extent after the second bout. No differences were observed in the responses in the health-related parameters in the control and in the statin therapy group. Eccentric exercise affected similarly the control and the atorvastatin-treated individuals. The present results indicate that atorvastatin-treated elderly individuals may participate in various physical activities, even high-intensity muscle-damaging activities, without negative impact on muscle function and adaptation.

Measuring changes in muscle stiffness after eccentric exercise using elastography

Muscle stiffness has been reported to increase following eccentric muscle exercise, but to date only indirect methods have been used to measure it. This study aimed to use Magnetic Resonance Elastography (MRE), a noninvasive imaging technique, to assess the time-course of passive elasticity changes in the medial gastrocnemius and soleus muscles before and after a bout of eccentric exercise. Shear storage modulus (G') and loss modulus (G'') measurements were made in eight healthy subjects for both muscles in vivo before, one hour after, 48 hours after and 1 week after eccentric exercise. The results show a 21% increase in medial gastrocnemius storage modulus following eccentric exercise with a peak occurring ~48 hours after exercise (before exercise 1.15 ± 0.23 kPa, 48 hours after 1.38 ± 0.27 kPa). No significant changes in soleus muscle storage modulus were measured for the exercise protocol used in this study, and no significant changes in loss modulus were observed. This study provides the first direct measurements in skeletal muscle before and after eccentric exercise damage and suggests that MRE can be used to detect the time course of changes to muscle properties.

Eccentric Exercise Facilitates Mesenchymal Stem Cell Appearance in Skeletal Muscle

Eccentric, or lengthening, contractions result in injury and subsequently stimulate the activation and proliferation of satellite stem cells which are important for skeletal muscle regeneration. The discovery of alternative myogenic progenitors in skeletal muscle raises the question as to whether stem cells other than satellite cells accumulate in muscle in response to exercise and contribute to post-exercise repair and/or growth. In this study, stem cell antigen-1 (Sca-1) positive, non-hematopoetic (CD45-) cells were evaluated in wild type (WT) and α7 integrin transgenic (α7Tg) mouse muscle, which is resistant to injury yet liable to strain, 24 hr following a single bout of eccentric exercise. Sca-1+CD45− stem cells were increased 2-fold in WT muscle post-exercise. The α7 integrin regulated the presence of Sca-1+ cells, with expansion occurring in α7Tg muscle and minimal cells present in muscle lacking the α7 integrin. Sca-1+CD45− cells isolated from α7Tg muscle following exercise were characterized as mesenchymal-like stem cells (mMSCs), predominantly pericytes. In vitro multiaxial strain upregulated mMSC stem cells markers in the presence of laminin, but not gelatin, identifying a potential mechanistic basis for the accumulation of these cells in muscle following exercise. Transplantation of DiI-labeled mMSCs into WT muscle increased Pax7+ cells and facilitated formation of eMHC+DiI− fibers. This study provides the first demonstration that mMSCs rapidly appear in skeletal muscle in an α7 integrin dependent manner post-exercise, revealing an early event that may be necessary for effective repair and/or growth following exercise. The results from this study also support a role for the α7 integrin and/or mMSCs in molecular- and cellular-based therapeutic strategies that can effectively combat disuse muscle atrophy.

ACUTE EXERCISE-INDUCED MUSCLE INJURY

While much research has recently been focussing on the chronic effects of overtraining, the acute damaging effects of individual eccentric exercise bouts on muscle remain of interest and underlie long-term training effects. Systemic markers of muscle damage are limited in terms of sensitivity and reliability. A clearer insight into the extent of the damage and mechanisms involved are being obtained from ultrastructural, functional and molecular examination of the muscle. There are currently indications that while the initial muscle damage may appear to have negative consequences in the short term, intense eccentric exercise appears to initiate a remodelling process and promote favourable adaptation of muscle following training, which has applications for promoting health, rehabilitation and sports performance.

The effects of acute alcohol consumption and eccentric muscle damage on neuromuscular function

Voluntary and electrically stimulated muscular performance was examined to identify the effects of acute alcohol consumption on neuromuscular function in the presence and absence of exercise-induced muscle damage (EIMD). After initial neuromuscular performance measures were made, 12 subjects completed a bout of eccentric exercise (EX) using the quadriceps muscles of 1 leg while the remaining 11 subjects did not exercise (NX). Subjects then consumed either an alcoholic beverage containing 1 g·kg(-1) body weight (ALC) or a nonalcoholic beverage (OJ). On another occasion the contralateral leg of both groups was tested and those in the EX group performed an equivalent bout of eccentric exercise after which the other beverage was consumed. Measurements of neuromuscular function were made pre-exercise and 36 and 60h post-beverage consumption. Creatine kinase (CK) was measured pre-exercise and at 12, 36, and 60h. Significantly greater (p< 0.01) decrements in maximal voluntary isometric contraction were observed with EX ALC at 36 and 60h compared with EX OJ, and no change was seen in the NX group. Significant decreases in voluntary activation were observed at 36h (p = 0.003) and 60h (p = 0.01) with EX ALC only. Elevations in CK were observed at all posteccentric exercise time points (all p< 0.05) under both EX OJ and ALC. No change in electromyography or low-frequency fatigue was observed under either treatment in either group. These results suggest that decreased neural drive appears to contribute to alcohol's effect on the magnitude of EIMD-related decrements in voluntary force generation.

Muscle fatigue experienced during maximal eccentric exercise is predictive of the plasma creatine kinase (CK) response

Unaccustomed eccentric exercise may cause skeletal muscle damage with an increase in plasma creatine kinase (CK) activity. Although the wide variability among individuals in CK response to standardized lengthening contractions has been well described, the reasons underlying this phenomenon have not yet been understood. Therefore, this study investigated a possible correlation of the changes in muscle damage indirect markers after an eccentric exercise with the decline in muscle performance during the exercise. Twenty-seven healthy untrained male subjects performed three sets of 30 maximal isokinetic eccentric contractions of the knee extensors. The muscular work was recorded using an isokinetic dynamometer to assess muscle fatigue by means of various fatigue indices. Plasma CK activity, muscle soreness, and stiffness were measured before (pre) and one day after (post) exercise. The eccentric exercise bout induced significant changes of the three muscle damage indirect markers. Large inter-subject variability was observed for all criteria measured. More interestingly, the log (CK(post) /CK(pre)) and muscle stiffness appeared to be closely correlated with the relative work decrease (r = 0.84, r(2) = 0.70 and r = 0.75, r(2) = 0.56, respectively). This is the first study to propose that the muscle fatigue profile during maximal eccentric protocol could predict the magnitude of the symptoms associated with muscle damage in humans.

Effects of set-repetition configuration in eccentric exercise on muscle damage and the repeated bout effect

The number of eccentric contractions is a factor affecting the magnitude of muscle damage; however, it is unknown whether set-repetition configurations for the same total number of eccentric contractions affect the muscle damage. The present study investigated whether different set-repetition configurations would result in different force output during eccentric exercise and different magnitude of muscle damage following the first and second exercise bouts. Ten non-resistance-trained men (26.1 ± 4.1 years) performed two bouts of eccentric exercise of the elbow flexors of each arm (4 bouts in total). One arm performed 3 sets of 10 maximal eccentric contractions (3 × 10) and the contralateral arm performed 10 sets of 3 maximal eccentric contractions (10 × 3), and each arm performed 20 sets of 3 maximal eccentric contractions (20 × 3) 4 weeks after the first bout. The order of the exercise (3 × 10, 10 × 3) and the use of arm (dominant, non-dominant) were counterbalanced amongst subjects. The torque produced over 30 eccentric contractions was similar between 3 × 10 and 10 × 3, and the changes in torque during 20 × 3 were similar between arms. Maximal voluntary contraction strength, range of motion, biceps brachii cross-sectional area and muscle soreness changed significantly (P < 0.05) following the exercise without significant differences between 3 × 10 and 10 × 3, and changes in the measures following 20 × 3 were similar between arms, except for range of motion (ROM). No significant difference in the changes in any measures except ROM was evident when compared between the first and second bouts. These results showed that changing the set-repetition configuration had little effect on muscle damage.

Influence of Acute Eccentric Exercise on the H:Q Ratio

The purpose of the present study was to examine the effects of an acute bout of eccentric exercise on maximal isokinetic concentric peak torque (PT) of the leg flexors and extensors and the hamstrings-to-quadriceps (H:Q) strength ratio. Sixteen male (mean±SD: age=20.9±2 years; stature=177.0±4.4 cm; mass=76.8±10.0 kg) volunteers performed maximal, concentric isokinetic leg extension and flexion muscle actions at 60°·sec - 1 before and after (24-72 h) a bout of eccentric exercise. The eccentric exercise protocol consisted of 4 sets of 10 repetitions for the leg press, leg extension, and leg curl exercises at 120% of the concentric one repetition maximum (1-RM). The results indicated that the acute eccentric exercise protocol resulted in a significant (P<0.05) decrease in isokinetic leg flexion (13-19%) and leg extension (11-16%) PT 24-72 h post-exercise. However, the H:Q ratios were unaltered by the eccentric exercise protocol. These findings suggest that an acute bout of eccentric exercise utilizing both multi - and single - joint dynamic constant external resistance (DCER) exercises results in similar decreases in maximal isokinetic strength of the leg flexors and extensors, but does not alter the H:Q ratio.

Effects of 14 days of prophylactic resveratrol supplementation in trained endurance runners upon the inflammatory markers TNF-a, IL1β, and IL-6 following a single bout of eccentric exercise

Background Resveratrolis a natural polyphenol found in peanuts and grapes. Resveratrolpossesses antioxidative properties which have shown to reduce the oxidative damage from reactive oxygen species (ROS). Resveratrol also has the ability to attenuate inflammation via inhibiting TNF-a, IL-1b, IL-6, and blocking NF-kB activation. Resveratrol supplementation may have the potential to mitigate the damages associated with intense orprolonged exercise; consequently improving recovery. The purpose of this study is to evaluate the effects of a14 day prophylactic supplementation trans-resveratrol onTNF-a, IL-1b ,a nd IL-6 from a single bout of eccentric exercise in traineddistance runners. Methods Eight trained male distance runners ages 35 to 45 (38.13 ± 2.95yrs) were randomly assigned to consume in a double blind manner either a placebo (PL) or 1000mg of transresveratrol (polygonum cuspidatum)(RESV) daily for 14 days (Transmax, BiotiviaBioceuticals). Prior to supplementation participants’ height (69.5 ± 2.3in) and weight (165.2 ± 24.25lbs.) were recorded and body composition (17.75 ± 4.8BF%) was assessed using DEXA. VO2max (55.3 ± 6.4 ml/kg/min) was assessed using Fox and Costill protocol and 65% of VO2max heart rate (117±4.2 bpm) was established for use as intensity predicator in the downhill running protocol. Following 14 days of prophylactic supplementation, participants engaged in a 45 minute downhill running protocol at 65% of VO2max at a declined grade of 12%. Venous blood samples were taken prior to (PRE), immediately after(POST), one hour (1HR) and two hours (2HR) following the downhill protocol. Serum samples for each time point (PRE,POST, 1HR, 2HR) were assayed for TNF-a, IL-1b ,a nd IL-6 using ELISA. Dietary analyses were conducted during the four days prior to testing to determine any antioxidant and anti-inflammatory influences within the diet. Results A significant main effect for time (p = 0.003) for IL-6 (RESV: 0.613±0.253, 1.38±0.394, 1.978±0.479, 1.594±0.66; PL: 0.921±0.73, 2.25±1.05, 1.698±0.561, 1.953±1.87 pg/mL). Delta responses for IL-6 showed a 125.12% change at POST, 222.68% change at 1HR, and 160.03% at 2HR for the RESV group while the PL group showed a 144.3%, 84.36%, and 112.05% change at the same time points, respectively. No significant observationsfor time or between groups for TNF-a and IL-1b were observed. Responsefrom baseline for TNF-a showed a 10.91% change at POST, 53.33% change at 1HR, and 8.48% at 2HR for the RESV group while the PL group showed a 15.3%, -1.87%, and -8.96% change at the same time points (p > 0.05), respectively. For IL-1b, the response from baseline showed a 10.96% change at POST, 16.04% change at 1HR, and 18.18% at 2HR for the RESV group while the PL group showed a -39.67%, -31.15%, and -33.93% change at the same time points (p >0 .05), respectively.No differences were observed on pain scale values between groups resulting from the eccentric protocol (p > 0.05).

The α7β1-integrin increases muscle hypertrophy following multiple bouts of eccentric exercise

Mechanical stimuli increase skeletal muscle growth in a mammalian target of rapamycin (mTOR)- and p70(S6K)-dependent manner. It has been proposed that costameric proteins at Z bands may sense and transfer tension to these initiators of protein translation, but few candidates have been identified. The purpose of this study was to determine whether a role exists for the α(7)-integrin in the activation of hypertrophic signaling and growth following eccentric exercise training. Five-week-old, wild-type (WT) and α(7)BX2-integrin transgenic (α(7)Tg) mice were randomly assigned to one of two groups: 1) sedentary (SED), or 2) exercise training (EX). Exercise training consisted of downhill running 3 sessions/wk for 4 wk (-20°, 17 m/min, 30 min). Downhill running was used to induce physiological mechanical strain. Twenty-four hours following the final training session, maximal isometric hindlimb plantar flexor force was measured. Gastrocnemius-soleus complexes were collected for further analysis of signaling changes, which included AKT, mTOR and p70(S6K), and muscle growth. Despite increased p70(S6K) activity in WT/EX, no significant changes in cross-sectional area or force were observed in WT/EX compared with WT/SED. AKT, mTOR, and p70(S6K) activation was higher, and whole muscle hypertrophy, relative muscle weight, myofibrillar protein, and force were significantly elevated in α(7)Tg/EX compared with α(7)Tg/SED. A marked increase in average myofiber cross-sectional area was observed in α(7)Tg/EX compared with all groups. Our findings demonstrate that the α(7)β(1)-integrin sensitizes skeletal muscle to mechanical strain and subsequent growth. Thus the α(7)β(1)-integrin may represent a novel molecular therapy for the treatment of disuse muscle atrophy.

The effects of vibration therapy on muscle force loss following eccentrically induced muscle damage

The purpose of this study was to investigate the effects of acute vibration therapy (VT) on performance recovery after a bout of strenuous eccentric exercise. Eight healthy males completed 300 maximal eccentric contractions of the quadriceps of one leg on an isokinetic dynamometer. Immediately after exercise and 12 and 24 h post-exercise, the subjects underwent either VT or a control treatment of no VT. Five sets of 1 min VT was performed at 26 Hz, with 6 mm peak-to-peak displacement, on a commercially available vibration machine. At least 2 weeks after the initial trial, the subjects completed the second trial using the contralateral leg and other treatment. Peak and average peak isometric tension and isokinetic concentric and eccentric torque were measured prior to exercise and 24 and 48 h post-exercise. Treatment with VT resulted in significantly (all P < 0.05) greater decrements in peak (-38%) and average peak eccentric (-39%) torque 24 h after eccentric exercise as compared to a control treatment (-24 and -29%, respectively). These results suggest that the use of 26 Hz VT in the first 24 h after damaging exercise may be detrimental to the magnitude of force loss and/or recovery over this period.

The α7β1-integrin accelerates fiber hypertrophy and myogenesis following a single bout of eccentric exercise

The α(7)β(1)-integrin is a heterodimeric transmembrane protein that adheres to laminin in the extracellular matrix, representing a critical link that maintains structure in skeletal muscle. In addition to preventing exercise-induced skeletal muscle injury, the α(7)-integrin has been proposed to act as an intrinsic mechanosensor, initiating cellular growth in response to mechanical strain. The purpose of this study was to determine the extent to which the α(7)-integrin regulates muscle hypertrophy following eccentric exercise. Wild-type (WT) and α(7)-integrin transgenic (α(7)Tg) mice completed a single bout of downhill running exercise (-20°, 17 m/min, 60 min), and gastrocnemius-soleus complexes were collected 1, 2, 4, and 7 days (D) postexercise (PE). Maximal isometric force was maintained and macrophage accumulation was suppressed in α(7)Tg muscle 1D PE. Mean fiber cross-sectional area was unaltered in WT mice but increased 40% in α(7)Tg mice 7D PE. In addition, a rapid and striking fivefold increase in embryonic myosin heavy chain-positive fibers appeared in α(7)Tg mice 2D PE. Although Pax7-positive satellite cells were increased in α(7)Tg muscle 1D PE, the number of nuclei per myofiber was not altered 7D PE. Phosphorylation of mammalian target of rapamycin (mTOR) was significantly elevated in α(7)Tg 1D PE. This study provides the first demonstration that the presence of the α(7)β(1)-integrin in skeletal muscle increases fiber hypertrophy and new fiber synthesis in the early time course following a single bout of eccentric exercise. Further studies are necessary to elucidate the precise mechanism by which the α(7)-integrin can enhance muscle hypertrophy following exercise.

Exercise-induced muscle damage and the repeated bout effect: evidence for cross transfer

We examined whether a prior bout of eccentric exercise in the elbow flexors provided protection against exercise-induced muscle damage in the contralateral arm. Fifteen males (age 22.7 ± 2.1 years; height 178.6 ± 6.8 cm, mass 75.8 ± 9.3 kg) were randomly assigned to two groups who performed two bouts of 60 eccentric contractions (30°/s) separated by 2 weeks: ipsilateral (n = 7, both bouts performed in the same arm), contralateral (n = 8, one bout performed in each arm). Strength, muscle soreness and resting arm angle (RAA) were measured at baseline and at 1, 24 and 48 h post exercise. Surface electromyography was recorded during both bouts of exercise. The degree of strength loss was attenuated (p < 0.05) in the ipsilateral group after the second bout of eccentric exercise (-22 cf. -3% for bout 1 and 2 at 24 h, respectively). Strength loss following eccentric exercise was also attenuated (p < 0.05) at 24 h in the contralateral group (-30 cf. 13% for bout 1 and 2, respectively). Muscle soreness (≈34 cf 19 mm) and change in RAA (≈5 cf. 3%) were also lower following the second bout of eccentric exercise (p < 0.05), although there was no difference in the overall change in these values between groups. Median frequency (MF) was decreased by 31% between bouts, with no difference between groups. Data support observations that the repeated bout effect transfers to the opposite (untrained) limb. The similar reduction in MF between bouts for the two groups provides evidence for a centrally mediated, neural adaptation.

Rate Of Velocity Development Less Decreased Following The Repeated Bout Of Maximal Eccentric Exercise

It has been reported that rate of velocity development (RVD) and strength are two of important measures of athletic performance, and eccentric exercise-induced muscle damage can be impaired RVD and strength performance (Nguyen et al., 2009 JSRC). It is well-documented that a bout of eccentric exercise confers protection against muscle damage after a subsequent bout of the same exercise performed several weeks to several months later (Clarkson et al., 1992 MSSE), but no study has examined effect of repeated bout of eccentric exercise on changes in RVD. PURPOSE: This study was to test the hypothesis that a repeated bout of maximal eccentric exercise of the elbow flexors would be less decreased RVD and faster recovery in comparison with the first bout. METHODS: Ten untrained young men (21.0 ± 3 yrs) performed 2 bouts of 30 maximal eccentric exercises (MAX1 & MAX2; 30°/s) of the elbow flexors of the non-dominant arm separated by 2 weeks. Maximal isokinetic concentric strength (MVC) and RVD (300°/s), muscle soreness, and range of motion were measured before, immediately after, and for 5 consecutive days after each bout. All data was analyzed by a two-way repeated measures ANOVA. RESULTS: The first bout of maximal eccentric exercise produced significant (P<0.05) decrease in maximal concentric strength (39%), RVD (49%), range of motion, and increase in muscle soreness. The changes in all criterion measures (e.g. MVC: 30%, RVD: 44%) after the second bout of the same exercise were significantly smaller (P<0.05) than that of the first bout. CONCLUSION: These results supported that MAX1 induced significantly muscle damage and soreness would be affected RVD, and protective effect occurred following the first bout of eccentric exercise results in a smaller decrease in RVD and faster recovery when the exercise is repeated after 2 weeks.

The Influence Of An Acute Bout Of Eccentric Exercise On The Hamstrings To Quadriceps Ratio

INTRODUCTION: The hamstrings to-quadriceps (H:Q) ratio has been used to assess the muscle balance at the knee joint. An imbalance of the flexor and extensor muscles at the knee joint has been shown to be associated with an increased risk for knee and hamstring related injuries. Eccentric training may potentially influence the (H:Q) ratio as it leads to an acute reduction in muscle force and impaired muscle function in the days following the workout. However, we are aware of no previous studies that have examined the effects of an acute bout of eccentric exercise on the H:Q ratio. PURPOSE: To examine the effects of a single bout of eccentric exercise on the H:Q ratio in recreationally active college age males. METHODS: Eight healthy male individuals (mean ± age = 20.75 ± 2.49 yr) volunteered to participate in the study. Isokinetic peak torque (IPT) of the right leg extensors and flexors were assessed on a Biodex System 2 dynamometer at 60° s-1. IPT was assessed 4 days prior to the eccentric workout protocol and again 24 hrs following the protocol. The eccentric workout consisted of four sets of 10 repetitions for the leg press, leg extension, and leg curl exercises that were performed at 120% of their predetermined concentric one repetition maximum. All exercises were performed on the right leg only. Conventional H:Q ratios were calculated by dividing the highest leg flexion IPT value by the highest leg extension IPT value. A paired samples t-test was used to analyze all data. An alpha of P ≤ 0.05 was used to determine statistical significance. RESULTS: The acute bout of eccentric exercise resulted in a significant decrease in IPT of the leg extensors (-10.93%, P = 0.007) and a non-significant decrease in IPT of the leg flexors (-5.90%, P = 0.138) at 24 hrs post eccentric training. There was no significant difference (P = 0.302) observed in the H:Q ratio following the acute eccentric exercise protocol. CONCLUSIONS: These findings indicated that a single bout of eccentric exercise reduced hamstring and quadriceps isokinetic strength, but did not influence the H:Q ratio. Thus, an acute bout of lower body eccentric exercise appears to not adversely affect muscular balance across the knee joint as measured from the H:Q ratio.

The Effect Of Muscle Recovery Drinks On Peak Torque Following An Eccentric Exercise Bout

PURPOSE: The purpose of this study was to exam the effects of consuming a protein drink containing a blend of whey protein (PRO) or an amino acid (AA) drink on muscle recovery following an intense bout of lower body eccentric exercise on leg extension and leg flexion peak torque (PT). METHODS: Twenty four male subjects volunteered to participate in this study. The subjects were randomly assigned to either the PRO (n=8, age=20.1+2.2 yrs, weight=84.7+13.8 kg, height=176.1+7.4 cm) AA (n=8, age=18.8+0.7 yrs, weight=78.1+ 14.8 kg, height=176.8+4.1 cm) or PL (n=8, age=20.8+2.5 yrs, weight=73.6+8.3 kg, height=176.1+4.1 cm) group. The study was approved by the university Institutional Review Board and each subject completed an informed consent and health history questionnaire. The subjects reported to the laboratory to perform strength testing on the dominant limb of the lower extremity in order to determine their one repetition maximum (1RM) for leg press, leg extension, and leg flexion. The subjects returned to perform three sets of three maximal leg extensions and flexions at 60 degrees per second on an isokinetic machine in order to determine baseline leg extension/flexion peak torque. Five days later the subjects were lead through a unilateral (dominant limb) high intensity eccentric resistance training protocol in order to elicit muscle soreness. Immediately following the exercise session the subjects received either the PRO, AA, or PL. Subjects then returned to the lab day 1, 2, 3, and 4 post eccentric training for isokinetic strength testing at 60 degrees per second (just like baseline testing mentioned above 3 sets of 3 reps). Immediately following each test session the subjects consumed their assigned drinks. RESULTS: Two (leg extension PT and leg flexion PT) group × time repeated measures ANOVA resulted in a non significant (p>0.05) group × time interaction with a significant (p<0.05) main effect for time. Therefore, the results of this study indicated that the subjects all recovered at an equally independent of their group assignment. CONCLUSIONS: In conclusion, the supplementation of either PRO or AA following a high intensity bout of lower body eccentric exercise did not significantly improve peak torque for leg flexion or leg extension when compared to the PL group.

Effects of a Repeated Bout of Eccentric Exercise on Skeletal Muscle Function and Gene Expression

Eccentric exercise (ECC) results in muscle damage indicated by reduced muscle function (soreness and strength loss). There is an adaptation to the damage such that the response to a second bout of ECC is reduced compared with the first bout. The underlying mechanisms that assist in the skeletal muscle remodeling process are largely unknown. The extracellular matrix (EM) protein tenascin-C (TNC) has been related to cardiac muscle remodeling in animals and muscle soreness in humans. PURPOSE: To examine whether gene expression of EM proteins are altered by a repeated bout of exercise. METHODS: 12 healthy subjects were randomized into the study, 8 (4 men/4 women) completed the two bouts of eccentric exercise (ECC) consisting of 15 descents of 10 flights of stairs and 4 (2 men/2 women) performed no exercise (CON). The 2 exercise bouts (ECC1 and ECC2) were separated by 2 wks. Skeletal muscle biopsies (MB) were taken from the vastus lateralis. The first biopsy (MB1, baseline) was taken 1wk before ECC1, the second (MB2) at 24 h post-ECC1, and the third (MB3) at 24 h post-ECC2. The CON subjects had three MB at the same time points. Samples were processed for qRT-PCR analysis for the following genes INTGB1, INTGA7, TNC, COL3, COL4, MMP9, MMP2, TIMP2, LAMA2. Samples were normalized to a housekeeping gene (B2M) and to then to their respective baseline sample (MB1). RESULTS: There was less soreness after ECC2 compared to ECC1. The major finding was that TNC was profoundly elevated after ECC1 (60.3 fold-change ±19.9; p<.05) and ECC2 (26.9 fold±12.5; p<.05). Control group values were 1.4 and 2.22 fold-change, respectively. INTGB3 was elevated after ECC1 and ECC2 (1.46±0.23 and 1.75±0.20 fold-change, p<.05), and there was a decrease from ECC1 to ECC2 (p<.05). Control group values were 0.59±0.19 and 0.96±0.14, respectively. No other genes changed significantly. CONCLUSION: Eccentric exercise profoundly elevated TNC, but there was no significant repeated about effect. There was a significant increase in INTGB1, a protein that connects the extracellular matrix and acts as a mechanotransducer for muscle. Overall, the extracellular matrix genes (except INTGB1) do not appear to be related to the repeated bout effect, but the increase in INTGB1 gene expression suggests some role for the ECM in the adaptation process that occurs with a repeated bout.

The α7B1 Integrin Promotes Skeletal Muscle Hypertrophy Following Eccentric Exercise

Myogenesis and/or new and preexisting fiber hypertrophy are primary factors responsible for muscle growth observed following eccentric exercise training. We have recently demonstrated that muscle-specific transgenic expression of the α7 integrin enhances de novo fiber synthesis in skeletal muscle following a single bout of eccentric exercise. PURPOSE: The purpose of this study was to determine the extent to which transgenic expression of the α7 integrin increases muscle fiber size and force generation following multiple bouts of eccentric exercise. METHODS: 5 wk old, female wild type (WT) (n=10) and α7BX2 integrin transgenic (α7Tg) (n=10) mice were randomly assigned to one of two groups: 1) sedentary (SED) or 2) exercise training (EX). Exercise training consisted of downhill running 3 times/wk for 4 wk (-20°, 17 m/min, 30 min). Twenty-four hr following the final training session, maximal isometric hindlimb plantarflexor force was measured via in situ stimulation of the sciatic nerve. Gastrocnemius-soleus complexes were collected for further analysis of fiber cross sectional areas (CSA). Analysis of signaling events reflective of protein synthesis (AKT and p70S6K) were completed on the contralateral limb. RESULTS: Whereas p70S6K phosphorylation was elevated 1.5-fold (P<0.05), no significant increases in average CSA (WT SED: 617.02 56.34 vs. WT EX: 847.77 76.18 mm2; NS), or hindlimb force were observed in the WT EX group compared to WT SED. In contrast, all AKT, mTOR and p70S6K phosphorylation were significantly elevated (AKT: 70%, mTOR: 2.0-fold; p70S6K: 1.3-fold; P<0.05) and concomitant increases in average CSA (α7Tg SED: 1280.80 62.25 mm2 vs. α7Tg EX: 1790.25 126.88; P<0.05) and hindlimb force (25.3%; P=0.054) were observed in the α7Tg EX group compared to α7Tg SED. The percentage of fibers ranging 2000 to 3000 mm2 increased 2.6-fold in α7Tg EX compared to α7Tg SED (P<0.05). CONCLUSION: The results from this study and our previous work demonstrate that the presence of the α7 integrin markedly enhances individual muscle fiber growth and suggest the α7B1 integrin is an important regulator of exercise-induced hypertrophy. Supported by grants from the Illinois Regenerative Medicine Institute, UIUC Arnold O. Beckman Award, and the Ellison Medical Foundation.

Repeated Bout Effect is not Correlated With Intraindividual Variability During Muscle-Damaging Exercise

The aim of this study was to test the hypothesis that the repeated bout effect depends on intraindividual variability during a second bout of eccentric exercise. Eleven healthy men performed 2 resistance training bouts consisting of maximal eccentric exercise (EE1 and EE2) using the knee extensor muscles. The interval between the exercise bouts was 2 weeks and consisted of 10 sets of 12 repetitions at 160° · s(-1). Maximal isokinetic concentric torque at 30° · s(-1) was measured before the bouts and 2 minutes and 24 hours thereafter. Muscle soreness score and creatine kinase activity were determined before and after exercise. Intraindividual variability in torque during each eccentric repetition was measured during exercise. Repeated bout effect manifested after EE2: Muscle soreness was less, the shift in optimal knee joint angle to a longer muscle length was less, and the decrease in isokinetic concentric torque 2 minutes after exercise was less for EE2 compared with that for EE1. During concentric (isokinetic) contraction, length-dependent changes in isokinetic torque (IT) occurred after both EE1 and EE2: The shorter the muscle length, the greater the change in IT. There was a significant relationship between the decrease in maximal isokinetic knee extension torque 24 hours after EE1 and intraindividual variability of EE1 (R2 = 0.71, p < 0.05), but this relationship was not significant for EE2 (R2 = 0.18). It seems that intraindividual variability during eccentric exercise protects against muscle fatigue and damage during the first exercise bout but not during a repeat bout. These findings may be useful to coaches who wish to improve muscle function in resistance training with less depression in muscle function and discomfort of their athletes, specifically, when muscle is most sensitive to muscle-damaging exercise.