Measuring changes in muscle stiffness after eccentric exercise using elastography

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

In Memoriam

The results regarding the effects of unaccustomed eccentric exercise on muscle tissue are often conflicting and the aetiology of delayed onset muscle soreness (DOMS) induced by eccentric exercise is still unclear. This study aimed to re-evaluate the paradigm of muscular alterations with regard to muscle sarcolemma integrity and fibre swelling in human muscles after voluntary eccentric exercise leading to DOMS. Ten young males performed eccentric exercise by downstairs running. Biopsies from the soleus muscle were obtained from 6 non-exercising controls, 4 exercised subjects within 1 hour and 6 exercised subjects at 2–3 days and 7–8 days after the exercise. Muscle fibre sarcolemma integrity, infiltration of inflammatory cells and changes in fibre size and fibre phenotype composition as well as capillary supply were examined with specific antibodies using enzyme histochemistry and immunohistochemistry. Although all exercised subjects experienced DOMS which peaked between 1.5 to 2.5 days post exercise, no significant sarcolemma injury or inflammation was detected in any post exercise group. The results do not support the prevailing hypothesis that eccentric exercise causes an initial sarcolemma injury which leads to subsequent inflammation after eccentric exercise. The fibre size was 24% larger at 7–8 days than at 2–3 days post exercise (p<0.05). In contrast, the value of capillary number per fibre area tended to decrease from 2–3 days to 7–8 days post exercise (lower in 5 of the 6 subjects at 7–8 days than at 2–3 days; p<0.05). Thus, the increased fibre size at 7–8 days post exercise was interpreted to reflect fibre swelling. Because the fibre swelling did not appear at the time that DOMS peaked (between 1.5 to 2.5 days post exercise), we concluded that fibre swelling in the soleus muscle is not directly associated with the symptom of DOMS.

All athletes have experienced the discomfort and debilitating effects of exercise-induced muscle damage. Symptoms are most common at the beginning of the season when intense training is reintroduced after a period of relative inactivity. A plethora of scientific data describes exercise conditions that lead to muscle damage. It is well accepted that damage occurs with unfamiliar exercise, primarily involving eccentric contractions. For example, downhill running places a large eccentric stress on the quadriceps muscle group and commonly results in muscle damage.1 However, muscles that have been preconditioned with eccentric contractions are protected against damage from subsequent bouts of eccentric exercise. This muscle damage is known as the “repeated-bout effect” and has been shown with various forms of exercise in both humans and animal models.2 Despite the many studies describing muscle damage and its various clinical symptoms, few have identified intrinsic causative factors or suitable interventions for limiting the symptoms. Clinically, it is important to first identify people at risk of developing more severe symptoms and then to design interventions that might limit those symptoms. Three recent experimental studies provide clinically relevant information for athletes and physicians.3,4,5 Controlled experimental studies have shown wide variation in symptoms between subjects after a bout of unfamiliar eccentric exercise. These data indicate that some people are more susceptible to damage than others, but it is not clear why. Recently musculoskeletal flexibility has been shown to be an important factor affecting the severity of symptoms after eccentric exercise.3 Flexibility was quantified according to a measure of passive muscle stiffness, and subjects' muscles were categorized as “stiff,” “normal,” or “compliant.” After a bout of eccentric exercise, subjects with stiff muscles had significantly greater loss of strength, pain, muscle tenderness, and elevation of plasma creatine kinase activity than those with compliant muscles. Greater apparent muscle damage was attributed to the inability of the tendon and aponeurosis of stiffer muscles to absorb the lengthening imposed by the eccentric contractions. Warm-up and stretching are known to greatly reduce muscle stiffness.6 Because stiffness seems to predispose muscles to damage, it follows that appropriately warming up before exercise may reduce the severity of exercise-induced muscle damage. It has also been shown that warm-up reduces subsequent symptoms of muscle damage.4 Eccentric contractions of the elbow flexors preceded by a warm-up resulted in significantly less loss of strength and elevation of plasma creatine kinase activity than eccentric contractions without a prior warm-up. The protective effect was attributed to decreased passive muscle stiffness, although actual stiffness measurements were not made. Besides the possible role of warm-ups in limiting the symptoms of muscle damage, preconditioning the muscle with eccentric contractions clearly provides a protective effect (repeated-bout effect). Recent data suggest that it may not be necessary to damage the muscle with the initial bout to provide a protective effect.5 Brown and associates showed that as few as 10 maximal eccentric contractions of the knee extensors were sufficient to reduce symptoms appreciably after a subsequent bout of 50 maximal contractions performed three weeks later. There was a clear repeated-bout effect despite that 10 contractions did not result in appreciable muscle damage. These data indicate that preconditioning muscles with a few maximal eccentric contractions can considerably reduce symptoms after a subsequent, more intense, bout of eccentric exercise. The key elements for the repeated-bout effect are that the preconditioning contractions are eccentric, that high-intensity contractions are performed, and that the preconditioning contractions affect the same muscle groups that will be working eccentrically in the repeated bout. All dynamic sports activities involve a large component of high-intensity eccentric contractions, whether the activity is in a game or a practice. Athletes typically experience considerable symptoms of muscle damage when returning to these activities after a prolonged layoff because of injury or between seasons. The severity of these symptoms may be reduced by maintaining good flexibility, especially of the principal muscle groups involved in the given sport; preconditioning the principal muscle groups with a few high-intensity eccentric contractions one to two weeks before returning to full activities; and performing specific warm-up exercises for the principal muscle groups immediately before the first few training sessions or games. Increasing the athletes' awareness of the cause of symptoms will increase compliance with any intervention directed at limiting muscle damage. This is especially important in sports that do not place a large emphasis on warm-up or flexibility.

Morawetz, D, Blank, C, Koller, A, Arvandi, M, Siebert, U, and Schobersberger, W. Sex-related differences after a single bout of maximal eccentric exercise in response to acute effects: a systematic review and meta-analysis. J Strength Cond Res 34(9): 2697-2707, 2020-The most prominent effects after unaccustomed eccentric exercise are muscle damage, muscle soreness, strength loss, and higher concentrations of muscle proteins in the plasma. The aim of this systematic review is to evaluate sex-related differences in these acute effects. A systematic literature search in MEDLINE following the PRISMA guidelines was performed. Inclusion criteria were the difference in absolute outcomes between sexes in eccentric muscle strength, strength loss after eccentric exercise, blood concentrations of creatine kinase (CK), and delayed onset muscle soreness (DOMS). Results for maximal eccentric torque and CK data were pooled using a random-effect meta-analysis. A meta-regression was conducted to explain heterogeneity. Based on the 23 included trials, men showed significantly higher absolute eccentric strength. No sex-related differences were detected when normalizing strength for body mass, cross-sectional area of the muscle, or fat-free mass. Women displayed a tendency toward greater relative strength loss immediately after exercise. The absolute CK concentrations of men were significantly higher after exercise-induced muscle damage. No significant difference was found between sexes in DOMS. Untrained men and women display similar responses in all measures of relative muscle strength and DOMS. Apart from the enzymatic activity after exercise and the levels of absolute eccentric torque, there is no evidence for sex-related differences immediately after eccentric exercise. Therefore, eccentric training might have the same impact on men and women. One potential sex difference with practical relevance would be the possible difference in fatigue pattern immediately after eccentric exercise.

ABSTRACTPurposeUnilateral resistance training increases muscle strength of the contralateral homologous muscle by the cross-education effect. Muscle damage induced by second eccentric exercise bout is attenuated, even when it is performed by the contralateral limb. The present study compared the effects of unilateral eccentric training (ET) and concentric training (CT) of the elbow flexors (EF) on maximal voluntary isometric contraction (MVC) strength and muscle damage of the contralateral untrained EF.MethodsYoung men were placed into ET, CT, ipsilateral repeated bout (IL-RB), and contralateral repeated bout (CL-RB) groups (n = 12 per group). The ET and CT groups performed unilateral EF training consisting of five sets of six eccentric and concentric contractions, respectively, once a week for 5 wk by increasing the intensity from 10% to 100% of MVC, followed by 30 maximal eccentric contractions (30MaxEC) of the opposite EF 1 wk later. The IL-RB group performed two bouts of 30MaxEC separated by 2 wk using the nondominant arm, and CL-RB group performed two bouts of 30MaxEC with a different arm for each bout in 1-wk apart.ResultsThe MVC increased (P < 0.05) greater for the trained (19% ± 8%) and untrained (11% ± 5%) arms in ET when compared with those in CT (10% ± 6%, 5% ± 2%). The magnitude of changes in muscle damage markers was reduced by 71% ± 19% after the second than the first bout for IL-RB group, and by 48% ± 21% for CL-RB group. Eccentric training and CT attenuated the magnitude by 58% ± 25% and 13% ± 13%, respectively, and the protective effect of ET was greater (P < 0.05) than CL-RB, but smaller (P < 0.05) than IL-RB.ConclusionsThese results showed that cross-education effect was stronger for ET than CT, and progressive ET produced greater contralateral muscle damage protective effect than a single eccentric exercise bout.

Is It Possible to Individualize Intensity of Eccentric Cycling Exercise From Perceived Exertion on Concentric Test?

The purpose was to investigate eccentric (ECC) exercise with full range of motion (FROM) induce a greater magnitude of delayed onset muscle soreness (DOMS), pain, functional limitations compared to partial range of motion (PROM; outer 60° of ROM). Thirty-four participants (men and women) aged between 18 and 30 years performed ECC exercise protocol on elbow and knee muscles (5 × 10 repetitions each session) using their 15%/25%/35% of maximal voluntary isometric contraction (MVIC) with PROM (week 2-4) and FROM (week 6-8). Two days a week, ECC exercises and remaining days the subjective and objective assessments were carried out (activities of daily living (ADL), pain (visual analogue scale (VAS), pain pressure threshold (PPT)), and MVIC. The ECC exercise with FROM showed moderate pain (0-3.5) in ADL (pulling a heavy object and descending stairs), VAS, and PPT for elbow extensors and knee flexors and showed a statistically significant difference (p ≤ 0.05) compared to PROM ECC protocol. The muscle strength was increased in FROM ECC exercise than PROM ECC exercise and ranged between 23.16% and 28.22%. ECC exercise performed with FROM induced a higher degree of DOMS, pain, ADL limitations than PROM. The study outcomes can be used for beginner sedentary older adults as well as young athletes.

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

Resistance Exercise and Knee Osteoarthritis

Does eccentric-exercise-induced jaw muscle soreness influence brainstem reflexes?

Muscle passive stiffness increases less after the second bout of eccentric exercise compared to the first bout

The purpose of this study was to assess if the protective adaptation after eccentric exercise affects changes of twitch contractile properties of the biceps brachii muscle. Maximal isometric torque (MVC), twitch contractile properties, muscle soreness, and relaxed elbow angle (RANG) assessments were measured in 12 untrained, right-handed male volunteers (age, 23 ± 2 years; height, 182 ± 5 cm; mass, 75 ± 7 kg) before, immediately after, 48 h, and 120 h following each bout of eccentric exercise that consisted of 30 repetitions of lowering a dumbbell adjusted to 75% of each individual's maximal isometric torque of the right elbow flexors. MVC, peak twitch torque, maximal rate of twitch torque development, maximal rate of relaxation, muscle soreness, and RANG changes were significantly attenuated after the second bout of eccentric exercise when compared with the first bout. In contrast, time to twitch peak torque and half relaxation time did not change significantly after both the first and the second bout. The findings indicate that the mechanisms responsible for rapid adaptation affect some twitch mechanical properties such as peak torque, maximal rate of torque development, and maximal rate of relaxation but not time to peak torque and half relaxation time.

We investigated the existence of contralateral repeated bout effect and tested if the attenuation of nuclear factor-kappa B (NF-κB; an important regulator of muscle inflammation) induction following eccentric exercise is a potential mechanism. Thirty-one healthy men performed two bouts of knee extension eccentric exercise, initially with one leg and then with the opposite leg 4 wk later. Vastus lateralis muscle biopsies of both exercised and control legs were taken 3 h postexercise. Knee extension isometric and isokinetic strength (60°/sec and 180°/sec) were measured at baseline, pre-exercise, immediately postexercise, and 1/day for 5 days postexercise. Serum creatine kinase (CK) activity and muscle soreness were assessed at baseline and 1/day for 5 days postexercise. NF-κB (p65) DNA-binding activity was measured in the muscle biopsies. Isometric strength loss was lower in bout 2 than in bout 1 at 24, 72, and 96 h postexercise (P < 0.05). Isokinetic strength (60°/s and 180°/s) was reduced less in bout 2 than in bout 1 at 72 h postexercise (P < 0.01). There were no significant differences between bouts for postexercise CK activity or muscle soreness. p65 DNA-binding activity was increased following eccentric exercise (compared with the control leg) in bout 1 (122.9% ± 2.6%; P < 0.001) and bout 2 (109.1% ± 3.0%; P < 0.05). Compared with bout 1, the increase in NF-κB DNA-binding activity postexercise was attenuated after bout 2 (P = 0.0008). Repeated eccentric exercise results in a contralateral repeated bout effect, which could be due to the attenuated increase in NF-κB activity postexercise.

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.