Eccentric Bout Research Articles

Mild to moderate damage in knee extensor muscles accumulates after two bouts of maximal eccentric contractions.

This study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days. Thirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course. Two days after the initial eccentric session, participants from EXP had a higher strength deficit (-14.5 ± 10.6%) than CON (-6.6 ± 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 ± 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%). Although the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage.

Knee position sense and knee flexor neuromuscular function are similarly altered after two submaximal eccentric bouts.

This study examined eccentric-induced fatigue effects on knee flexor (KF) neuromuscular function and on knee position sense. This design was repeated across two experimental sessions performed 1week apart to investigate potential repeated bout effects. Sixteen participants performed two submaximal bouts of KF unilateral eccentric contractions until reaching a 20% decrease in maximal voluntary isometric contraction force. Knee position sense was evaluated with position-matching tasks in seated and prone positions at 40° and 70° of knee flexion so that KF were either antagonistic or agonistic during the positioning movement. The twitch interpolation technique was used to assess KF neuromuscular fatigue. Perceived muscle soreness was also assessed. Measurements were performed before, immediately (POST) and 24h after (POST24) each eccentric bout. No repeated bout effect on neuromuscular function and proprioceptive parameters was observed. At POST, central and peripheral factors contributed to the force decrement as shown by significant decreases in voluntary activation level (-3.8 ± 4.8%, p < 0.01) and potentiated doublet torque at 100Hz (-10 ± 15.8%, p < 0.01). At this time point, position-matching errors significantly increased by 1.7 ± 1.9° in seated position at 40° (p < 0.01). At POST24, in presence of muscle soreness (p < 0.05), although KF neuromuscular function had recovered, position-matching errors increased by 0.6 ± 2.6° in prone position at 40° (p < 0.01). These results provide evidence that eccentric-induced position sense alterations may arise from central and/or peripheral mechanisms depending on the testing position.

Plasma α-Actin as an Early Marker of Muscle Damage After Repeated Bouts of Eccentric Cycling

ABSTRACT Purpose: This study aimed to examine the changes in skeletal muscle (SM) α-actin, myoglobin (Mb) and hydroxyproline (HP) in plasma and other indirect markers of muscle damage after repeated bouts of eccentric cycling. Methods: Ten healthy men (23.3 ± 2.8 years) performed two 30-min eccentric cycling bouts at 100% of maximal concentric power output (230.7 ± 36.9 W) separated by 2 weeks (ECC1 and ECC2). Maximal voluntary isometric contraction (MVIC) peak force of the knee extensor muscles, muscle soreness (SOR), pain pressure threshold (PPT) and plasma levels of SM α-actin, Mb, and HP were measured before, 0.5, 3, 24–168 h after each cycling bout. Results: MVIC peak force decreased on average 10.7 ± 13.1% more after ECC1 than ECC2. SOR was 80% greater and PPT was 12–14% lower after ECC1 than ECC2. Plasma SM α-actin levels increased at 0.5, 3, and 24–72 h after ECC1 (26.1–47.9%), and SM α-actin levels at 24 h after ECC1 were associated with muscle strength loss (r = −0.56, P = .04) and SOR (r = 0.88, P = .001). Mb levels increased at 0.5, 3, and 24 h after ECC1 (200–502%). However, Mb levels at 24 h after ECC1were not associated with muscle strength loss and SOR. HP levels remained unchanged after ECC1. ECC2 did not increase SM α-actin, Mb and HP levels. Conclusion: Our results indicate that α-actin could be used as a potential marker for the early identification of SM damage due to its early appearance in plasma and its association with other indirect markers of muscle damage.

The Effects of Spirulina Supplementation on Redox Status and Performance Following a Muscle Damaging Protocol

Spirulina plantensis is a popular supplement which has been shown to have antioxidant and performance enhancing properties. The purpose of this study was to evaluate the effects of spirulina supplementation on (a) redox status (b) muscle performance and (c) muscle damage following an eccentric bout of exercise that would induce muscle damage. Twenty-four healthy, recreationally trained males participated in the study and were randomly separated into two groups: a spirulina supplementation (6 g per day) and a placebo group. Both groups performed an eccentric bout of exercise consisting of 5 sets and 15 maximum reps per set. Blood was collected at 24, 48, 72 and 96 h after the bout and total antioxidant capacity (TAC) and protein carbonyls (PC) were assessed in plasma. Delayed onset muscle soreness (DOMS) was also assessed at the same aforementioned time points. Eccentric peak torque (EPT) was evaluated immediately after exercise, as well as at 24, 48, 72 and 96 h post exercise. Redox status indices (TAC and PC) did not change significantly at any time point post exercise. DOMS increased significantly 24 h post exercise and remained elevated until 72 h and 96 h post exercise for the placebo and spirulina group, respectively. EPT decreased significantly and immediately post exercise and remained significantly lower compared to baseline until 72 h post exercise. No significant differences between groups were found for DOMS and EPT. These results indicate that spirulina supplementation following a muscle damaging protocol does not confer beneficial effects on redox status, muscle performance or damage.

Metabolic Demand and Indirect Markers of Muscle Damage After Eccentric Cycling With Blood Flow Restriction

ABSTRACT Purpose: To compare the effects of a single bout of eccentric cycling (ECC) and eccentric cycling with blood flow restriction (ECCBFR) on the changes in cardio-metabolic demand and indirect markers of muscle damage in healthy men. Method: Twenty-one young men (24.0 ± 3.2 y) were randomly allocated in two groups to perform a 30-min eccentric cycling bout with or without blood flow restriction. Oxygen consumption, heart rate, rate of perceived exertion and mean arterial blood pressure were monitored during cycling. Blood lactate was measured before and after cycling. Maximal voluntary isometric knee extensor strength and muscle damage were measured before, immediately after and 1–4 days after each eccentric cycling bout. Results: Oxygen consumption, heart rate, rate of perceived exertion and mean arterial blood pressure were similar between bouts. Blood lactate concentrations increased in both groups (p < .01), with ECCBFR showing 60% greater blood lactate concentration than eccentric cycling (p < .01). Maximal voluntary isometric knee extensor strength decreased 19-7% until 48 h and decreased 16-7% until 72 h after ECC and ECCBFR, respectively. Muscle soreness and pressure pain threshold remained elevated until 72 h after ECC and until 96 h after ECCBFR. Conclusion: These results show that ECCBFR induces similar cardiovascular stress, greater lactate production and longer time to recover than ECC alone. Thus, BFR can be safely implemented with eccentric cycling.

Changes in arterial stiffness after eccentric versus concentric cycling.

This study compared changes in brachial-ankle pulse wave velocity (baPWV) after concentric (CON) versus eccentric (ECC) cycling. It was hypothesized that baPWV would increase after the first ECC bout (ECC1) because of muscle damage, but not after the second ECC bout (ECC2), and would decrease after CON. Fifteen young (aged 20-30 years) men performed 2 bouts of 30-min ECC (ECC1 and ECC2) at 60% of maximal CON power output and 2 bouts of 30-min CON at the same intensity as that of ECC (CON1), and at the same oxygen consumption as that of ECC (CON2) every 2 weeks. Oxygen uptake during the cycling was recorded, and baPWV was measured before and at 0.5, 1, 24, and 48 h after each cycling bout. Maximal voluntary contraction (MVC) torque and muscle soreness of the knee extensors were assessed before and at 24 and 48 h after each cycling bout. Changes in these variables over time were compared among the 4 cycling bouts by 2-way repeated-measured ANOVA. baPWV decreased (P < 0.05) 8% from the baseline (1119 ± 116 cm/s) at 0.5 h after CON1 (1028 ± 126 cm/s), but no significant changes were evident after ECC1, ECC2, and CON2. MVC torque decreased 10% from the baseline at 24 h after ECC1, but no significant changes were evident after CON1, CON2, and ECC2. These results did not support the hypothesis, and suggest that minor muscle damage induced by eccentric cycling does not affect arterial stiffness.

ALTERATIONS OF ECCENTRICALLY EVOKED PROTEIN SYNTHESIS IN ISOLATED RAT SOLEUS FOLLOWING GRAVITATIONAL UNLOADING: ROLE OF FAK

ALTERATIONS OF ECCENTRICALLY EVOKED PROTEIN SYNTHESIS IN ISOLATED RAT SOLEUS FOLLOWING GRAVITATIONAL UNLOADING: ROLE OF FAK

Using first bout effect to study the mechanisms underlying eccentric exercise induced force loss

IntroductionThe first bout of eccentric exercise is known to have a protective effect on the consequent bouts. This effect is still disputable as it is not known whether it protects muscle damage by reducing force production or by improving force recovery in the healing process. The underlying mechanisms of this protective effect have not been fully understood. ObjectivesTo determine the mechanisms of this protective effect, three different loads were used for the first eccentric bout. This was done to investigate whether the protective effect is related to the size of the load in the first bout. To determine the neural adaptations, voluntary activation was assessed and to determine the muscular adaptations, the resting twitch was measured. MethodThirty healthy participants were selectively allocated into three groups (low-, moderate- and high-load group) to match for maximal voluntary contraction (MVC) (n = 10 per group). Participants in each group performed only one of the three sets of ten eccentric (ECC) exercises of the elbow flexors (10%, 20% and 40% of MVC) as their first eccentric bout. The second bout of eccentric exercise was performed two weeks later and was identical for all the three groups, i.e., 40% ECC. ResultsThe results showed that for the first bout, MVC, voluntary activation and the resting twitch displayed significant (p < 0.0001) interaction (group x time). This was not the case however for the second bout as there was no significant (group x time) interaction in all outcome variables immediately after exercise. When the first and second bouts were compared, it was found that the high-load group had faster recovery in MVC at day 1 and 4 corresponding to voluntary activation and only at day 4 corresponding to the resting twitch. ConclusionsIn this study, it was found that high-load exercise aids fast recovery either via neural or muscular adaptations.

Diclofenac pretreatment modulates exercise-induced inflammation in skeletal muscle of rats through the TLR4/NF-κB pathway.

Nonsteroidal anti-inflammatory drugs, such as diclofenac, are widely used to treat inflammation and pain in several conditions, including sports injuries. This study analyzes the influence of diclofenac on the toll-like receptor-nuclear factor kappa B (TLR-NF-κB) pathway in skeletal muscle of rats submitted to acute eccentric exercise. Twenty male Wistar rats were divided into 4 groups: control-saline, control-diclofenac, exercise-saline, and exercise-diclofenac. Diclofenac or saline were administered for 7 days prior to an acute eccentric exercise bout. The inflammatory status was evaluated through mRNA levels of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), IL-1β, and tumor necrosis factor alpha (TNF-α), and protein content of COX-2, IL-6, and TNF-α in vastus lateralis muscle. Data obtained showed that a single bout of eccentric exercise significantly increased COX-2 gene expression. Similarly, mRNA expression and protein content of other inflammation-related genes also increased after the acute exercise. However, these effects were attenuated in the exercise + diclofenac group. TLR4, myeloid differentiation primary response gene 88 (MyD88), and p65 were also upregulated after the acute eccentric bout and the effect was blunted by the anti-inflammatory drug. These findings suggest that pretreatment with diclofenac may represent an effective tool to ameliorate the pro-inflammatory status induced by acute exercise in rat skeletal muscle possibly through an attenuation of the TLR4-NF-κB signaling pathway.

In Memoriam

In Memoriam

TLR4-mediated blunting of inflammatory responses to eccentric exercise in young women.

This study assessed the inflammatory response mediated by the toll-like receptor 4 (TLR4) signaling pathway after acute eccentric exercise before and after an eccentric training program in women. Twenty women performed two acute eccentric bouts using a squat machine over a ~9 week interval. The training group (TG) carried out an eccentric training program during 6 weeks, while the control group (CG) did not follow any training. Protein content of markers involved in the TLR4-mediated activation of several nuclear transcription factors, such as nuclear factor κB (NF-κB), and interferon regulatory transcription factor 3 (IRF3), was analyzed. The inflammatory response after the first acute bout was similar between TG and CG, showing an upregulation of all the markers analyzed, with the exception of IRF3. After the second bout, the upregulation of TLR4 signaling pathway was blunted in TG, but not in CG, through both the myeloid differentiation factor 88- and toll/interleukin-1 receptor domain containing adapter inducing interferon-β-dependent pathways. These results highlight the role of the TLR4 in controlling the exercise-induced inflammatory response in young women. More importantly, these data suggest eccentric training may help to prevent TLR4 activation principally through NF-κB, and perhaps IRF3, downstream signaling in this population.

The susceptibility of the knee extensors to eccentric exercise‐induced muscle damage is not affected by leg dominance but by exercise order

The aims of this study were first to compare the response of dominant and non-dominant legs to eccentric exercise and second, to examine whether there is an effect of exercise order on the magnitude of symptoms associated with intense eccentric protocols. Eighteen young men performed three sets of 30 maximal eccentric isokinetic (60° s(-1)) contractions of the knee extensors (range of motion, ROM: 0°-100°, 0 = full extension) using either dominant or non-dominant leg. They repeated a similar eccentric bout using the contralateral leg 6 weeks later. The sequence of leg's use was allocated to create equally balanced groups. Four indirect markers of muscle damage including subjective pain intensity, maximal isometric strength, muscle stiffness and plasma creatine kinase (CK) activity were measured before and 24 h after exercise. All markers changed significantly following the eccentric bout performed either by dominant or non-dominant legs, but no significant difference was observed between legs. Interestingly, the comparison between the first and second eccentric bouts revealed that muscle soreness (-42%, P<0.001), CK activity (-62%, P<0.05) and strength loss (-54%, P<0.01) were significantly lower after the second bout. This study suggests that leg dominance does not influence the magnitude of exercise-induced muscle damage and supports for the first time the existence of a contralateral protection against exercise-induced muscle damage in the lower limbs.

Effect of Brief Intense TENS and Cryotherapy on the Symptoms Associated with Delayed Onset of Muscle Soreness in Healthy Male Subjects

Objective: The study investigated the effect of brief intense TENS and ice on pain relaxed elbow extension angle. Design and setting: Three sets of concentric and eccentric action induced delayed onset of the elbow flexors of non dominant hand. Pre exercise measures were recorded for relaxed elbow extension range and perceived muscle pain. Group A received ice treatment for 15 minutes, group B received brief intense TENS (100 Hz, 100 milliseconds, maximum tolerable intensity), Group C received sham TENS treatments after 48 hours of post-exercise. Subjects: Forty five healthy male subjects Measurements: Relaxed elbow extension angle and perceived muscle pain was recorded before exercise, before treatment after 48 hours post exercise and after treatment. Results: Readings were compared for difference using ANOVA it was found that there was statistically significant difference p=0.045 (p Conclusion: Cryotherapy was effective in reducing the perceived pain in elbow flexors after eccentric bouts

Specific training improves skeletal muscle mitochondrial calcium homeostasis after eccentric exercise

There is limited understanding of the mitochondrial adaptation following repeated eccentric exercise bouts, a model resulting in muscle adaptation known as the repeat bout effect. It was hypothesized that downhill training would reduce mitochondrial calcium content (MCC) post an acute eccentric bout with concurrent improvements in mitochondrial respiratory function. Thirty-four Sprague-Dawley rats were divided into four groups: control (N), control with acute eccentric exercise (N (ecc)), trained control (X) and trained with acute eccentric exercise (X (ecc)). Training for X and X (ecc) consisted of 30min per day for five consecutive days of downhill treadmill running. The acute eccentric exercise bout was a -14° treadmill exercise for 90min performed 2weeks after the training period. Animals were killed 48h post-exercise. Isolated mitochondria from the red quadriceps allowed for the measure of mitochondrial respiratory indices and MCC. Calpain activity and heat shock protein 72 expression (HSP72) were also measured. MCC dramatically increased following the acute bout of eccentric exercise in N (ecc) (p<0.001), but did not change in X (ecc). Mitochondrial respiratory function tended to be slightly depressed in N (ecc) (state 3 respiration, p=0.053; respiratory control ratio, p=0.098) and unaltered in X (ecc). Previous training altered the calpain and heat shock protein response to an acute bout of eccentric exercise. The results suggest that downhill exercise training improves mitochondrial calcium homeostasis following an acute bout of prolonged eccentric exercise and may stabilize mitochondrial respiratory function. These improvements coincide with a reduction in calpain activity and heat shock protein upregulation.

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.

The Effect of Muscular Endurance on Running Economy

The purpose of this study was to examine the relationship between fatigue-induced changes in running economy (RE) and muscular strength endurance (MSE). Ten well-trained male runners completed 2 runs of the same energy expenditure at 20%Δ VO(2) below LT. In the middle of the experimental condition (high intensity exercise [HIE]), there was a 4-minute block at sVO(2)max. The aim of the 4-minute block was to increase RE through fatigue, without inducing exhaustion. The MSE of hip extensors (HEs) and knee flexors (KFs) was assessed by 2 20-second eccentric bouts on an isokinetic dynamometer at 180°·s(-1). The RE increased after HIE compared to the control condition. Partial correlations found the increase in RE was strongly related with KF MSE (r = -0.709-0.798; p = 0.03-0.01). Greater MSE appeared to confer a fatigue resistant effect, resulting in a smaller increase in RE. The underlying mechanism of the fatigue resistant effect remains to be elucidated. Conditioning work focusing on augmenting eccentric muscular endurance of the legs may offer beneficial adaptations that promote fatigue resistance.

Effects Of Concentric And Eccentric Muscle Contractions On Il-6 Signaling In Human Skeletal Muscle And Downstream Regulation Of Hsp-72 Gene Expression

Inflammation response in exercise of healthy humans is significantly different than that which is commonly reported for chronic inflammatory conditions. Regardless of the scenario, cytokines such as Tumor Necrosis Factor (TNF)-α and Interleukin (IL)-1b have demonstrated pro-inflammatory functions, while IL-6 has demonstrated versatile pro- and anti-inflammatory roles when exercise is a factor. Prolonged skeletal muscle contractions of sufficient intensity have been shown to induce significant muscle protein damage and a complex inflammatory cascade involving IL-6 and, separately, Heat Shock Proteins (HSP), and components of the Mitogen-Activated Protein Kinase (MAPK) pathway. This cascade not completely understood in any scenario, particularly in humans. Thus the role of inflammation in regards to exercise, particularly resistance training, has not been elucidated. To determine the effects of concentric (CON) and eccentric (ECC) contractions on creatine kinase (CK), lactate dehydrogenase (LDH), and IL-6 signaling in regards to IL-1b, TNF-α, HSP-72, Nuclear Factor-kappa B (NF-?B), p38 MAPK, Signal Transducer and Activator of Transcription (STAT)-1 and STAT-3 and the potential cytoprotection HSP-27. Six active males (19.33 ± 1.03 yrs; 181.94 ± 6.40 cm; 72.83 ± 12.78 kg) participated in two separate bouts of 10 × 10 unilateral isokinetic knee extensions at 30°/sec. Each bout consisted of either CON or ECC contractions on either the right or left leg; each contraction type and leg was utilized once for each subject. Isokinetic strength tests were performed five days pre- and 24 and 48 hours post-exercise. Serum CK, LDH, IL-6, IL-1b, and TNF-α were assessed immediately preexercise (PRE), immediately post-exercise (PX), and at 2, 6, 24, and 48 hr PX. IL-6, HSP-27, and HSP-72, NF-?B, p38 MAPK, STAT-1 and STAT-3 protein and mRNA expression of IL-6, HSP-27, and HSP-72 were assessed from vastus lateralis biopsies (Bergstrom ) collected at PRE, PX, and 2 and 6 hr PX. Repeated measures MANOVAs and subsequent univariate analyses were performed on all data. Peak torque decreased (p < 0.05) at 24 and 48 hr PX. CK, but not LDH, increased (p < 0.05) similarly following CON and ECC. Serum cytokines were different (p < 0.05) between CON and ECC, but did not change over time. In muscle, NF-?B (p < 0.05) increased and STAT-1 decreased (p < 0.05). ECC contractions demonstrated significantly greater expression for IL-6, p38 MAPK, and STAT-3 than did CON, with a trend (p = 0.093) for STAT-1. There was significant CON/ECC interaction among NF-?B and STAT-1 and a trend (p = 0.074) for HSP-72. Skeletal muscle mRNA expression demonstrated no significant results. Both CON and ECC bouts demonstrated muscle damage and fatigue, but were not sufficient to induce a systemic inflammatory response. Intramuscular inflammatory response was most robust for NF-?B and STAT-1. The hypothesis of ECC stimulating the IL-6 pathway more so than CON is supported the relationship in expression of IL-6, p38 MAPK, STAT-1 and STAT-3. This is novel evidence of a relationship among these factors. Bouts of resistance exercise that include ECC contractions can favorably affect the exercise inflammation response; perhaps more so than lower intensity CON-only contractions.

Post-Eccentric Exercise Blunted hGH Response

The purpose of the present study was to test if a previous acute concentric exercise bout blunts hGH response after an eccentric exercise bout. Nine healthy untrained male university students (25.4+/-0.5 yr, 176.5+/-1.2 cm, and 79.4+/-2.0 kg) performed a concentric exercise bout followed by an eccentric exercise bout one week later. Serum human growth hormone (hGH), creatine kinase (CK), and lactate were measured before, immediately and up to 32 h after both exercise bouts. Higher lactate values were observed immediately, 5 and 10 min after the concentric bout (70%, 119%, and 142%, respectively, p<0.05) than the eccentric bout. There was a CK main time effect at 8 and 32 h after the exercise bouts compared to baseline values (p<0.002). However, peak serum CK effect size was higher after the concentric than the eccentric exercise bout, 1.3 and 0.9, respectively. hGH increased after both exercise bouts, however it reached significance only at immediately (207%), 5 min (256%), 10 min (276%), 20 min (300%), and 40 min (168%) after the concentric exercise bout (p<0.05). Our findings suggest that a previous concentric exercise bout may blunt the anabolic response expected after an eccentric exercise bout.

Intramuscular adaptations to eccentric exercise and antioxidant supplementation

Prophylactic supplementation of N-acetyl-cysteine (NAC) and epigallocatechin gallate (EGCG) was studied for physiological and cellular changes in skeletal muscle after eccentric muscle contractions. Thirty healthy, active males (20.0 +/- 1.8 years, 160 +/- 7.1 cm, 76.1 +/- 17.0 kg) ingested for 14 days either 1,800 mg of NAC, 1,800 mg of EGCG, or 1,000 mg of fiber (glucomannan) placebo (PLC) in a double blind, prophylactic fashion. Subjects completed one eccentric exercise bout (100 repetitions at 30 degrees /s) using the dominant knee extensors. Strength and soreness were assessed, and blood and muscle samples obtained before and 6, 24, 48, and 72 h with no muscle sample being collected at 72 h. Separate mixed factorial repeated measures ANOVA (P < 0.05) were used for all statistical analysis. All groups experienced significantly reduced peak torque production after 6 and 24 h, increased soreness at all time points from baseline [with even greater soreness levels 24 h after exercise in PLC when compared to EGCG and NAC (P < 0.05)], increased lactate dehydrogenase at 6 h, and increased creatine kinase 6, 24 and 48 h after exercise. No significant group x time interaction effects were found for serum cortisol, neutrophil counts, and the neutrophil:lymphocyte ratio; although, all values experienced significant changes 6 h after exercise (P < 0.05), but at no other time points. At 48 h after the exercise bout the Neu:Lym ratio in EGCG was significantly less than NAC (P < 0.05), whereas there was a trend (P = 0.08) for the EGCG values to be less when compared to PLC at this time point. Markers of intramuscular mitochondrial and cytosolic apoptosis were assessed (e.g., bax, bcl-2, cytochrome C, caspase-3 content/enzyme activity, and total DNA content). Significant increases (P < 0.05) in muscle levels of bax and bcl-2 were observed in all groups with no significant differences between groups, whereas no changes (P > 0.05) were reported for cytochrome C, caspase-3 content, caspase-3 enzyme activity, and total DNA. Caspase-3 enzyme activity was significantly greater in all groups 48 h after exercise when compared to baseline (P < 0.05) and 6 h (P < 0.05) after exercise. An eccentric bout of muscle contractions appears to significantly increase muscle damage, markers of mitochondrial apoptosis, apoptotic enzyme activity, and whole-blood cell markers of inflammation with no changes in oxidative stress. While soreness ratings were blunted in the two supplementation groups 24 h after exercise when compared to PLC values, more research is needed to determine the potential impact of EGCG and NAC supplementation on changes related to oxidative stress, apoptosis, and eccentric exercise.

Repeated bout effect is absent in resistance trained men: An electromyographic analysis

A prior bout of exercise is well known to confer protection from subsequent eccentric bouts (i.e. repeated bout effect; RBE), which may be fostered through neural adaptations, specifically a shift in the frequency content of the surface electromyogram (EMG). It is currently not clear whether chronically resistance trained men are capable of a RBE driven by neural adaptations. Eleven resistance trained men (23.5 ± 3.4 yrs) performed 100 eccentric actions of the barbell bench press exercise, followed by an equivalent bout 14 days later. Indirect markers of muscle damage (i.e. force production, soreness) along with surface EMG were measured before and through 48 h of recovery. Median frequency and maximal isometric force demonstrated time main effects ( p > 0.05), but no RBE. A prior bout of eccentric exercise does not confer a RBE for indirect markers of muscle injury or elicit changes in the frequency content of the EMG signal in resistance trained men.