Damage and the repeated bout effect of arm, leg, and trunk muscles induced by eccentric resistance exercises

Neuromuscular electrical stimulation producing low evoked force elicits the repeated bout effect on muscle damage markers of the elbow flexors

This study examined the repeated bout effect (RBE) on muscle damage markers following two bouts of neuromuscular electrical stimulation (NMES) in untrained individuals. Following familiarization, participants received 45 consecutive NMES to the biceps brachii at an intensity that produced low evoked force for the elbow flexors. Muscle damage markers (maximal voluntary isometric contraction [MVIC], elbow range of motion [ROM], muscle soreness via visual analogue scale [VAS] scores, pressure pain threshold [PPT], and muscle thickness) were measured before (PRE), after (POST), 1 day after (24 POST), and 2 days after (48 POST) NMES. Following 1 week of rest, procedures were replicated. Separate repeated measures two-way ANOVAs examined each measure. There were no interactions or bout main effects for MVIC or ROM. Time main effects indicated PRE MVIC was greater than POST (p ​= ​0.002) and 24-POST (p ​= ​0.024), and PRE ROM was greater than POST (p ​= ​0.036). There was no interaction for muscle thickness. Respective time and bout main effects indicated muscle thickness at PRE was less than POST (p ​= ​0.017), and second-bout muscle thickness (p ​= ​0.050) was less compared to the initial-bout. For PPT, there was an interaction (p ​= ​0.019). Initial-bout PRE PPT was less than POST (p ​= ​0.033). Initial-bout 48-POST PPT was less than second-bout 48-POST (p ​= ​0.037). There was a significant interaction for VAS (p ​= ​0.009). Initial-bout PRE VAS was less than POST (p ​= ​0.033) and 24-POST (p ​= ​0.015). Initial-bout POST and 24-POST VAS were greater than second-bout POST (p ​= ​0.023) and 24-POST (p ​= ​0.006), respectively. The results support RBE on muscle damage markers related to inflammation, but not MVIC and ROM.

Intracellular Ca 2+ After Eccentric Muscle Contractions: Key Role for Ryanodine Receptors

Eccentric contractions (ECC) induce excessive intracellular calcium ion (Ca 2+ ) accumulation and muscle structural damage in localized regions of the muscle fibers. In this investigation, we present the novel hypothesis that the ryanodine receptor (RyR) plays a central role in evoking a Ca 2+ dynamics profile that is markedly distinguishable from other muscle adaptive responses.

In vivo intracellular Ca2+ profiles after eccentric rat muscle contractions: addressing the mechanistic bases for repeated bout protection

Eccentric contractions (ECC) are accompanied by the accumulation of intracellular calcium ions ([Ca2+]i) and induce skeletal muscle damage. Suppressed muscle damage in repeated bouts of ECC is well characterized; however, whether it is mediated by altered Ca2+ profiles remains unknown. We tested the hypothesis that repeated ECC suppresses Ca2+ accumulation via adaptations in Ca2+ regulation. Male Wistar rats were divided into two groups: ECC single bout (ECC-SB) and repeated bout (ECC-RB). Tibialis anterior (TA) muscles were subjected to ECC (40 times, 5 sets) once (ECC-SB) or twice 14 days apart (ECC-RB). Under anesthesia, the TA muscle was loaded with Ca2+ indicator Fura 2-AM, and the 340/380 nm ratio was evaluated as [Ca2+]i. Ca2+ handling proteins were measured by Western blots. ECC induced [Ca2+]i increase in both groups, but ECC-RB evinced a markedly suppressed [Ca2+]i (Time: P < 0.01, Group: P = 0.0357). Five hours post-ECC, in contrast to the localized [Ca2+]i accumulation in ECC-SB, ECC-RB exhibited lower and more uniform [Ca2+]i (P < 0.01). In ECC-RB, mitochondria Ca2+ uniporter complex (MCU) components MCU and MICU2 were significantly increased pre-second ECC bout (P < 0.01), and both SERCA1 and MICU1 were better preserved after contractions (P < 0.01). Fourteen days after novel ECC, skeletal muscle mitochondrial Ca2+ regulating proteins were elevated. Following subsequent ECC, [Ca2+]i accumulation and muscle damage were suppressed and SERCA1 and MICU1 preserved. These findings suggest that tolerance to a subsequent ECC bout is driven, at least in part, by enhanced mitochondrial and sarcoplasmic reticulum Ca2+ regulation.NEW & NOTEWORTHY We demonstrated a reduced [Ca2+]i profile with suppressed muscle damage after a repeated bout of ECC in vivo: the ECC-induced immediate [Ca2+]i increase was suppressed and the persistence of increased [Ca2+]i with localized accumulation was diminished after repeated ECC. This effect occurred consonant with the upregulation of the mitochondrial Ca2+ uniporter complex and better preservation of SERCA1 and MICU1. These findings suggest that the mechanistic bases for repeated bout protection involve adaptation of Ca2+ regulation.

Effects of static stretching and specific warm-up on the repetition performance in upper- and lower-limb exercises in resistance-trained older women

INTRODUCTION

Preparation methods are often used to improve performance (e.g., number of repetitions) within the resistance training session. However, there is still no consensus in the scientific literature on whether there is a superior preparation method for improving performance, particularly in older adults.

METHODS

We compared the effects of preparation by specific warm-up (SW), static stretching (SS), and control condition (CC) on the total number of repetitions in four exercises: leg extension, triceps pushdown, seated leg curl, and preacher curl. Fifty-seven older women (≥ 60 years) performed the experimental protocols (SW and SS) and the CC in a cross-over and counterbalanced design. Following the preparation protocol, the main exercises were performed in two sets until volitional concentric failure, with a two-minute rest interval between sets and 2-3 min between exercises. The main outcome was the total number of repetitions.

RESULTS

The SS improved performance compared to the SW and the CC in the leg extension and seated leg curl resistance exercises. In contrast, the SW impaired performance compared to the SS and CC in the triceps pushdown and preacher curl exercises.

CONCLUSION

Our results suggest that SS may improve performance in lower-limb exercises, while the SW appears to negatively affect performance in upper-limb exercises in resistance-trained older women.

Effect of cold-water immersion treatment on recovery from exercise-induced muscle damage in the hamstring

This study investigated the effect of five consecutive days of cold-water immersion (CWI) on recovery from exercise-induced muscle damage (EIMD) in the hamstrings following maximal eccentric contraction (EC) exercise. Eighteen healthy adult women were randomly assigned to a CWI group and a control group (CG) (n = 9/group). Participants performed 10 sets of 10 repetitions of isokinetic EC at 30°/second and underwent maximum voluntary isometric contraction (MVC), delayed onset muscle soreness (DOMS) assessment, straight leg raise (SLR) test, and plasma myoglobin (Mb) measurement. The CWI group received one 14-min session of CWI treatment (14°C) at 1, 25, 49, 73, and 97 h after the EC test, whereas the CG rested in a seated position at the same five time points without receiving treatment. (1) All the dependent variables in the CWI group and CG exhibited significant changes after the EC test (p < 0.05). (2) The recovery effect in the CWI group was significantly greater than in the CG in terms of the MVC, DOMS, SLR, and plasma Mb concentration results. MVC increased by 89.3 ± 2.0% on the fourth day (p < 0.013), DOMS decreased by 15.4 ± 1.5 mm on the second day (p < 0.000), SLR increased by 86.3 ± 1.1% on the second day (p < 0.014), and plasma Mb decreased by 436.3 ± 60.8% on the third day (p < 0.014). The study indicates that five consecutive days of CWI at 14°C significantly enhance recovery from exercise-induced muscle damage in the hamstrings.

Oh, My Quad: A Clinical Commentary And Evidence-Based Framework for the Rehabilitation of Quadriceps Size and Strength after Anterior Cruciate Ligament Reconstruction

Quadriceps weakness after anterior cruciate ligament reconstruction (ACLR) is a well-known phenomenon, with more persistent quadriceps weakness observed after ACLR with a bone-patellar tendon-bone or quadriceps tendon autograft than with a hamstring tendon autograft. Longstanding quadriceps weakness after ACLR has been associated with suboptimal postoperative outcomes and the progression of radiographic knee osteoarthritis, making the recovery of quadriceps size and strength a key component of ACLR rehabilitation. However, few articles have been written for the specific purpose of optimizing quadriceps size and strength after ACLR. Therefore, the purpose of this review article is to integrate the existing quadriceps muscle basic science and strength training literature into a best-evidence synthesis of exercise methodologies for restoring quadriceps size and strength after ACLR, as well as outline an evidence-informed quadriceps load-progression for recovering the knee's capacity to manage the force-profiles associated with high-demand physical activity. Level of Evidence: 5.

Effects of Delayed-Onset Muscle Pain on Respiratory Muscle Function

BACKGROUND

Delayed-onset muscle soreness (DOMS) has been widely examined in the peripheral muscles; however, studies showing the potential effects of DOMS on respiratory function are limited.

HYPOTHESIS

DOMS in trunk muscles has a negative effect on respiratory function parameters, respiratory muscle strength, respiratory muscle endurance, and exercise capacity.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 2.

METHODS

In 24 healthy participants with a mean age of 21 ± 2 years, DOMS was induced for the trunk muscles with a load equal to 80% of the maximum repetitive voluntary contraction. Pulmonary function parameters, respiratory muscle strength and endurance, exercise capacity, pain, fatigue, and dyspnea perception severity were recorded before DOMS and at 24 and 48 hours after DOMS.

RESULTS

After DOMS, decreases were observed in respiratory function parameters, namely, forced vital capacity, forced expiratory volume in the first second, vital capacity, and 25% to 75% flow rate value of forced expiratory volume (25% to 75%) (P = 0.02, P = 0.02, P < 0.01, P = 0.01, respectively). Maximal inspiratory pressure and exercise capacity also decreased (P = 0.02, P < 0.01, respectively). No difference was observed between all 3 measurements of maximal expiratory pressure (MEP) and MEP% values (P1 = P2 = P3 ≥ 0.99). The results of the respiratory muscle endurance tests did not reveal a significant difference in terms of load and time in all 3 conditions (P > 0.05).

CONCLUSION

After DOMS, there was a 4% to 7.5% decrease in respiratory function parameters, and a 6.6% decrease in respiratory muscle strength.

CLINICAL RELEVANCE

The occurrence of DOMS before a competition can have a detrimental impact on pulmonary performance. Hence, it is imperative to consider this factor when devising training and exercise programs. In addition, the development of treatment protocols becomes crucial if DOMS arises.

Elevated Plasma IL-6 Coincides with Activation of STAT3 in PBMC After Acute Resistance Exercise

INTRODUCTION

Changes in plasma concentrations of anti-inflammatory cytokines, such as interleukin-6 (IL-6) and IL-10, after acute resistance exercise (RE) have been widely explored. Whether observed changes in plasma cytokine concentration correspond to the activation of anti-inflammatory signaling pathways in immune cells after acute RE is unknown. This study aimed to determine if changes in plasma cytokines after acute RE resulted in the activation of anti-inflammatory signaling pathways in peripheral blood mononuclear cells (PBMC).

METHODS

Healthy young males (N = 16; age = 23.5 ± 2.7 yr; BMI = 22.4 ± 1.7 kg·m-2) participated in a single session of whole-body RE (4 sets of 4 different exercises at 70% 1-repetition maximum with the last set to failure) and a sedentary control (CON) condition in a randomized crossover design. Blood samples were collected at several time points before and after the exercise bout.

RESULTS

Higher plasma IL-6, IL-10, and IL-1 RA concentrations were observed after RE compared with CON. Phosphorylation of STAT3 and protein expression of SOCS3 in PBMC were increased in RE compared with CON. The elevation of plasma IL-6, but not IL-10, coincided with the activation of STAT3 signaling in PBMC.

CONCLUSIONS

These results highlight a potential mechanism by which RE may exert anti-inflammatory actions in circulating immune cells.

Bigger Calves from Doing Higher Resistance Training Volume?

We compared the effects of different weekly calf training sets on muscle size changes. Sixty-one untrained young women performed a calf training program for 6 weeks, 3 d·wk-1, with differences in resistance training volume. The participants were randomly assigned to one of the three groups: 6-SET, 9-SET, and 12-SET weekly calf training sets. The calf raise exercise was performed in sets of 15-20 repetitions maximum. The muscle thickness measurements of medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) were taken via B-mode ultrasound. We used the sum of the three-muscle thickness as a proxy for the triceps surae (TSSUM). The 12-SET group elicited greater increases than the 6-SET in LG (6-SET=+ 8.1% vs. 12-SET=+ 14.3%; P=0.017), SOL (6-SET=+ 6.7% vs. 12-SET=+ 12.7%; P=0.024), and TSSUM (6-SET=+ 6.9% vs. 12-SET=+ 12.0%; P=0.005), but there was no significant difference in MG changes (6-SET=+ 6.6% vs. 12-SET=+ 9.9%; P=0.067). There were no significant differences when comparing 9-SET vs. 6-SET and 12-SET (P≥0.099). Although all groups experienced calf muscle hypertrophy, our results suggest that the higher dose range may optimize triceps surae muscle size gains.

Eccentric exercise-induced delayed onset trunk muscle soreness alters high-density surface EMG-torque relationships and lumbar kinematics

We aimed to assess high-density surface electromyography (HDsEMG)-torque relationships in the presence of delayed onset trunk muscle soreness (DOMS) and the effect of these relationships on torque steadiness (TS) and lumbar movement during concentric/eccentric submaximal trunk extension contractions. Twenty healthy individuals attended three laboratory sessions (24 h apart). HDsEMG signals were recorded unilaterally from the thoracolumbar erector spinae with two 64-electrode grids. HDsEMG-torque signal relationships were explored via coherence (0-5 Hz) and cross-correlation analyses. Principal component analysis was used for HDsEMG-data dimensionality reduction and improvement of HDsEMG-torque-based estimations. DOMS did not reduce either concentric or eccentric trunk extensor muscle strength. However, in the presence of DOMS, improved TS, alongside an altered HDsEMG-torque relationship and kinematic changes were observed, in a contraction-dependent manner. For eccentric trunk extension, improved TS was observed, with greater lumbar flexion movement and a reduction in δ-band HDsEMG-torque coherence and cross-correlation. For concentric trunk extensions, TS improvements were observed alongside reduced thoracolumbar sagittal movement. DOMS does not seem to impair the ability to control trunk muscle force, however, perceived soreness induced changes in lumbar movement and muscle recruitment strategies, which could alter motor performance if the exposure to pain is maintained in the long term.

Pre-exercise cryotherapy reduces myoglobin and creatine kinase levels after eccentric muscle stress in young women

Introduction: The aim of this study was to investigate the effect of pre-exercise whole-body cryotherapy (WBC) on muscle damage indicators following eccentric treadmill exercise in young women. Methods: Twenty-seven participants underwent two 1-h downhill treadmill runs, replicating 60% of their maximal oxygen uptake, with a 4-week intermission for recovery and treatment application. In this intermission, one group underwent 20 sessions of WBC, delivered five times a week at -120°C for 3 min each, while the comparison group received no such treatment. Markers of muscle injury-serum myoglobin concentration, creatine kinase and lactate dehydrogenase activity and also uric acid, and cell-free DNA concentration-were measured before and after downhill runs. Results: The study observed a notable reduction in post-exercise myoglobin and CK levels in the WBC group after the second running session. Discussion: The results suggest that WBC can have a protective effects against muscle damage resulting from eccentric exercise.

Reduction in systemic muscle stress markers after exercise-induced muscle damage following concurrent training and supplementation with specific collagen peptides - a randomized controlled trial

Introduction

Collagen peptide supplementation in conjunction with exercise has been shown to improve structural and functional adaptations of both muscles and the extracellular matrix. This study aimed to explore whether specific collagen peptide (SCP) supplementation combined with a concurrent training intervention can improve muscular stress after exercise-induced muscle damage, verified by reliable blood markers.

Methods

55 sedentary to moderately active males participating in a concurrent training (CT) intervention (3x/week) for 12 weeks were administered either 15 g of SCP or placebo (PLA) daily. Before (T1) and after the intervention (T2), 150 muscle-damaging drop jumps were performed. Blood samples were collected to measure creatine kinase (CK), lactate dehydrogenase (LDH), myoglobin (MYO) and high-sensitivity C-reactive protein (hsCRP) before, after, and at 2 h, 24 h and 48 h post exercise.

Results

A combination of concurrent training and SCP administration showed statistically significant interaction effects, implying a lower increase in the area under the curve (AUC) of MYO (p = 0.004, ηp2 = 0.184), CK (p = 0.01, ηp2 = 0.145) and LDH (p = 0.016, ηp2 = 0.133) in the SCP group. On closer examination, the absolute mean differences (ΔAUCs) showed statistical significance in MYO (p = 0.017, d = 0.771), CK (p = 0.039, d = 0.633) and LDH (p = 0.016, d = 0.764) by SCP supplementation.

Conclusion

In conclusion, 12 weeks of 15 g SCP supplementation combined with CT intervention reduced acute markers of exercise-induced muscle damage and improved post-exercise regenerative capacity, as evidenced by the altered post-exercise time course. The current findings indicate that SCP supplementation had a positive effect on the early phase of muscular recovery by either improving the structural integrity of the muscle and extracellular matrix during the training period or by accelerating membrane and cytoskeletal protein repair.

Clinical trial registration

https://www.clinicaltrials.gov/study/NCT05220371?cond=NCT05220371&rank=1, NCT05220371.

Associations of resistance training levels with low muscle mass: a nationwide cross-sectional study in Korea

BACKGROUND

Low muscle mass is associated with adverse health outcomes such as functional decline and all-cause mortality. This study investigated the relationship between the risk of low muscle mass and the training period and/or frequency of resistance training (RT).

METHODS

We included 126,339 participants (81,263 women) from nationwide cohorts in Korea. Low muscle mass was defined based on the fat-free mass index. To investigate the presence of an inverse dose-response relationship between RT levels and the risk of low muscle mass, the training period (months) and frequency (per week) of RT were used. Multiple logistic regression models were used to assess the risk of low muscle mass according to the RT levels.

RESULTS

Prevalence rates for low muscle mass in our study population were 21.27% and 6.92% in men and women, respectively. When compared with not performing RT, performing RT for 3-4 days/week and ≥5 days/week decreased the risk of low muscle mass by 22% and 27%, respectively, and performing RT for 12-23 months and ≥24 months decreased the risk by 19% and 41%, respectively. When simultaneously considering both training period and frequency, performing RT for either 3-4 days/week or ≥5 days/week was significantly related to risk reduction, provided that the training period was at least 1 year. Importantly, performing RT for more than 2 years resulted in an additional risk reduction. However, there was no additional effect of performing RT for ≥5 days/week compared to 3-4 days/week, regardless of whether the RT duration was 1-2 years or more than 2 years.

CONCLUSIONS

Since performing RT for 5 days/week or more did not yield any additional effects on the risk of low muscle mass, performing RT for 3-4 days/week was sufficient to prevent low muscle mass. The effectiveness of this preventive measure can be further enhanced by engaging in long-term RT, specifically for more than 2 years.

Brain activation associated with low- and high-intensity concentric versus eccentric isokinetic contractions of the biceps brachii: An fNIRS study

Studies have shown that neural responses following concentric (CON) and eccentric (ECC) muscle contractions are different, which suggests differences in motor control associated with CON and ECC contractions. This study aims to determine brain activation of the left primary motor cortex (M1) and left and right dorsolateral prefrontal cortices (DLPFCs) during ECC and CON of the right bicep brachii (BB) muscle at low- and high-contraction intensities. Eighteen young adults (13M/5F, 21-35 years) were recruited to participate in one familiarization and two testing sessions in a randomized crossover design. During each testing session, participants performed either ECC or CON contractions of the BB (3 sets × 8 reps) at low- (25% of maximum ECC/CON, 45°/s) and high-intensity (75% of maximum ECC/CON, 45°/s) on an isokinetic dynamometer. Eleven-channel functional near-infrared spectroscopy was used to measure changes in oxyhemoglobin (O2 Hb) from the left M1, and left and right DLPFC during ECC and CON contractions. Maximum torque for ECC was higher than CON (43.3 ± 14.1 vs. 46.2 ± 15.7 N m, p = 0.025); however, no differences in O2 Hb were observed between contraction types at low or high intensities in measured brain regions. High-intensity ECC and CON contractions resulted in greater increases in O2 Hb of M1 and bilateral DLPFC compared to low-intensity ECC and CON contractions (p = 0.014). Our findings suggest no differences in O2 Hb responses between contraction types at high and low intensities. High-contraction intensities resulted in greater brain activation of the M1 and bilateral DLPFC, which may have implications for neurorehabilitation to increase central adaptations from exercise.

Overview of muscle fatigue differences between maximal eccentric and concentric resistance exercise

Since the 1970s, researchers have studied a potential difference in muscle fatigue (acute strength loss) between maximal eccentric (ECCmax ) and concentric (CONmax ) resistance exercise. However, a clear answer to whether such a difference exists has not been established. Therefore, the aim of our paper was to overview methods and results of studies that compared acute changes in muscle strength after bouts of ECCmax and CONmax resistance exercise. We identified 30 relevant studies. Participants were typically healthy men aged 20-40 years. Exercise usually consisted of 40-100 isokinetic ECCmax and CONmax repetitions of the knee extensors or elbow flexors. Both ECCmax and CONmax exercise caused significant strength loss, which plateaued and rarely exceeded 60% of baseline, suggesting strength preservation. In upper-body muscles, strength loss at the end of ECCmax (31.4 ± 20.4%) and CONmax (33.6 ± 17.5%) exercise was similar, whereas in lower-body muscles, strength loss was less after ECCmax (13.3 ± 12.2%) than CONmax (39.7 ± 13.3%) exercise. Muscle architecture and daily use of lower-body muscles likely protects lower-body muscles from strength loss during ECCmax exercise. We also reviewed seven studies on muscle fatigue during coupled ECCmax -CONmax exercise and found similar strength loss in the ECC and CON phases. We also found evidence from three studies that more ECC than CON repetitions can be completed at equal relative loads. These results indicate that muscle fatigue may manifest differently between ECCmax and CONmax resistance exercise. An implication of the results is that prescriptions of ECC resistance exercise for lower-body muscles should account for greater fatigue resilience of these muscles compared to upper-body muscles.

Evaluation of a preemptive intervention regimen with hesperidin methyl chalcone in delayed-onset muscle soreness in young adults: a randomized, double-blinded, and placebo-controlled trial study

PURPOSE

Delayed-onset muscle soreness (DOMS) describes an entity characterized by ultrastructural muscle damage. Hesperidin methyl chalcone (HMC) is a synthetic flavonoid presenting analgesic, anti-inflammatory, and antioxidant properties. We evaluated the effects of HMC upon DOMS.

METHOD

In a preventive paradigm, 31 sedentary young men were submitted to a randomized, double-blinded parallel trial and received HMC 500 mg or one placebo capsule × 3 days before an intense dynamic exercise protocol (concentric/eccentric actions) applied for lower limbs for inducing muscle damage. Assessments were conducted at baseline, and 24 and 48 h after, comprising physical performance, and post-muscle soreness and damage, inflammation, recovery of muscle strength, and postural balance associated with DOMS. HMC safety was also evaluated. Thirty participants completed the study.

RESULTS

HMC improved the performance of participants during exercise (40.3 vs 51.3 repetitions to failure, p = 0.0187) and inhibited CPK levels (90.5 vs 57.9 U/L, p = 0.0391) and muscle soreness during passive quadriceps palpation (2.6 vs 1.4 VAS cm, p = 0.0439), but not during active actions, nor did it inhibit IL-1β or IL-10 levels. HMC improved muscle strength recovery, and satisfactorily refined postural balance, without inducing injury to kidneys or liver.

CONCLUSIONS

Preemptive HMC supplementation may be beneficial for boosting physical performance and for the amelioration of clinical parameters related to DOMS, including pain on muscle palpation, increased blood CPK levels, and muscle strength and proprioceptive deficits, without causing adverse effects. These data advance the understanding of the benefits provided by HMC for DOMS treatment, which supports its usefulness for such purpose.

Increased muscle force does not induce greater stretch-induced damage to calf muscles during work-matched heel drop exercise

PURPOSE

To investigate the effect of muscle force during active stretch on quantitative and qualitative indicators of exercise-induced muscle damage (EIMD) in the medial gastrocnemius (MG) muscle.

METHODS

Twelve recreationally active volunteers performed two trials of an eccentric heel drop exercise. Participants performed a single bout of low-load (body weight) and high-load (body weight + 30% body weight) exercises on separate legs. The total mechanical work output for each condition was matched between legs. Before, two hours and 48 h after each bout of eccentric exercise, electrically stimulated triceps surae twitch torque, muscle soreness, MG active fascicle length at maximum twitch torque and muscle passive stiffness were collected. Triceps surae electromyographic (EMG) activity, MG fascicle stretch and MG muscle-tendon unit (MTU) length were measured during the eccentric tasks.

RESULTS

The high-load condition increased triceps surae muscle activity by 6-9%, but reduced MG fascicle stretch (p < 0.001). MTU stretch was similar between conditions. The greater muscle force during stretch did not give rise to additional torque loss (5 vs 6%) or intensify muscle soreness.

CONCLUSIONS

Adding 30% body weight during eccentric contractions has a modest impact on exercise-induced muscle damage in the medial gastrocnemius muscle. These results suggest that muscle load may not be an important determinant of stretch-induced muscle damage in the human MG muscle. The muscle investigated does exhibit large pennation angles and high series elastic compliance; architectural features that likely buffer muscle fibres against stretch and damage.

Muscle Damage, Inflammation, and Muscular Performance following the Physical Ability Test in Professional Firefighters

Proper monitoring of fatigue and muscular damage may be used to decrease the high levels of cardiovascular disease, overuse musculoskeletal injuries, and workers compensation claims within the profession of firefighting. The purpose of this study was to examine muscle damage, muscular fatigue, and inflammation responses following a typical firefighting shift. Twenty-four professional firefighters completed two Physical Ability Tests to standardize the tasks typically performed in a day of work, and to elicit similar physiological responses. Participants were then monitored for 48 h. Prior to, and 48 h following the Physical Ability Tests, participants were evaluated for changes in strength, power, range-of-motion, as well as blood markers including myoglobin and c-reactive protein. Following the Physical Ability Tests, significant differences in myoglobin (p < 0.05), grip strength (p < 0.05), vertical jump (p < 0.05), and sit-and-reach (p < 0.05) were observed. No difference in c-reactive protein was observed (p > 0.05). After 24 hours following a shift, firefighters exhibited decreased strength, power, and range-of-motion. This may lead to decreases in performance and an increased risk of injury.

Recovery from Resistance Exercise in Older Adults: A Systematic Scoping Review

BACKGROUND

Resistance exercise is recommended for maintaining muscle mass and strength in older adults. However, little is known about exercise-induced muscle damage and recovery from resistance exercise in older adults. This may have implications for exercise prescription. This scoping review aimed to identify and provide a broad overview of the available literature, examine how this research has been conducted, and identify current knowledge gaps relating to exercise-induced muscle damage and recovery from resistance exercise in older adults.

METHODS

Studies were included if they included older adults aged 65 years and over, and reported any markers of exercise-induced muscle damage after performing a bout of resistance exercise. The following electronic databases were searched using a combination of MeSH terms and free text: MEDLINE, Scopus, Embase, SPORTDiscus and Web of Science. Additionally, reference lists of identified articles were screened for eligible studies. Data were extracted from eligible studies using a standardised form. Studies were collated and are reported by emergent theme or outcomes.

RESULTS

A total of 10,976 possible articles were identified and 27 original research articles were included. Findings are reported by theme; sex differences in recovery from resistance exercise, symptoms of exercise-induced muscle damage, and biological markers of muscle damage.

CONCLUSIONS

Despite the volume of available data, there is considerable variability in study protocols and inconsistency in findings reported. Across all measures of exercise-induced muscle damage, data in women are lacking when compared to males, and rectifying this discrepancy should be a focus of future studies. Current available data make it challenging to provide clear recommendations to those prescribing resistance exercise for older people.

Resistance exercise: a mighty tool that adapts, destroys, rebuilds and modulates the molecular and structural environment of skeletal muscle

PURPOSE

Skeletal muscle regulates health and performance by maintaining or increasing strength and muscle mass. Although the molecular mechanisms in response to resistance exercise (RE) significantly target the activation of protein synthesis, a plethora of other mechanisms and structures must be involved in orchestrating the communication, repair, and restoration of homeostasis after RE stimulation. In practice, RE can be modulated by variations in intensity, continuity and volume, which affect molecular responses and skeletal muscle adaptation. Knowledge of these aspects is important with respect to planning of training programs and assessing the impact of RE training on skeletal muscle.

METHODS

In this narrative review, we introduce general aspects of skeletal muscle substructures that adapt in response to RE. We further highlighted the molecular mechanisms that control human skeletal muscle anabolism, degradation, repair and memory in response to acute and repeated RE and linked these aspects to major training variables.

RESULTS

Although RE is a key stimulus for the activation of skeletal muscle anabolism, it also induces myofibrillar damage. Nevertheless, to increase muscle mass accompanied by a corresponding adaptation of the essential substructures of the sarcomeric environment, RE must be continuously repeated. This requires the permanent engagement of molecular mechanisms that re-establish skeletal muscle integrity after each RE-induced muscle damage.

CONCLUSION

Various molecular regulators coordinately control the adaptation of skeletal muscle after acute and repeated RE and expand their actions far beyond muscle growth. Variations of key resistance training variables likely affect these mechanisms without affecting muscle growth.

Fish Oil Supplementation Improves the Repeated-Bout Effect and Redox Balance in 20-30-Year-Old Men Submitted to Strength Training

Herein, we investigated the effect of fish oil supplementation combined with a strength-training protocol, for 6 weeks, on muscle damage induced by a single bout of strength exercise in untrained young men. Sixteen men were divided into two groups, supplemented or not with fish oil, and they were evaluated at the pre-training period and post-training period. We investigated changes before and 0, 24, and 48 h after a single hypertrophic exercise session. Creatine kinase (CK) and lactate dehydrogenase (LDH) activities, plasma interleukin-6 (IL-6) and C-reactive protein (CRP) levels, and the redox imbalance were increased in response to the single-bout session of hypertrophic exercises at baseline (pre-training period) and decreased during the post-training period in the control group due to the repeated-bout effect (RBE). The fish oil supplementation exacerbated this reduction and improved the redox state. In summary, our findings demonstrate that, in untrained young men submitted to a strength-training protocol, fish oil supplementation is ideal for alleviating the muscle injury, inflammation, and redox imbalance induced by a single session of intense strength exercises, highlighting this supplementation as a beneficial strategy for young men that intend to engage in strength-training programs.

The Contralateral Repeated Bout Effect of Elbow Flexors Is Not Observed in Young Women Following Mild Muscle Damage from Eccentric Exercises

Investigation of the contralateral repeated bout effect (CL-RBE) in women is scarce. Therefore, this study aimed at examining whether CL-RBE exists in women. Twelve healthy women (age: 20.9 ± 2.5 years) performed two bouts of maximal elbow flexor eccentric exercise (3 sets × 15 repetitions per bout) separated by 14 days, using the opposite arms. Surface Electromyography (EMG) was recorded during both exercise bouts. The isokinetic muscle strength (60°/s), muscle soreness, range of motion (ROM), limb girth, and blood creatine kinase activity were measured pre-exercise, and at 24 and 48 h post-exercise with the muscle strength being measured immediately post-exercise as well. Significant main effects of time were observed for muscle strength, muscle soreness and ROM (p < 0.05). There were no significant differences between bouts for all the measured variables including the EMG median frequency (p > 0.05). These results suggest that the CL-RBE of elbow flexors was not evident in young healthy women. This was because the mild muscle damage induced by the initial bout of exercise was either not enough to initiate the CL-RBE or the CL-RBE in women lasted shorter than two weeks. This study provides important information for future studies on CL-RBE in women.

Exercise induced muscle damage and repeated bout effect: an update for last 10 years and future perspectives

Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations. EIMD is the muscle damage occurring after one bout of unaccustomed exercise while RBE is the attenuation of the same muscle damage in subsequent second bout. RBE seems to have significant implications for exercise prescription. Despite existence of vast literature, there is lack of clarity on the effects of EIMD and RBE in a healthy population. The purpose of this study is to review the literature on EIMD and RBE in healthy participants published during the last 10 years. The search of major databases (including Scopus, Google Scholar and PubMed) was conducted using specific keywords ‘Exercise induced muscle damage’, ‘Repeated bout effect’, ‘Healthy participants’ ‘Pre-conditioning’, ‘Eccentric exercise’. Studies published from 2011 onwards which included EIMD and RBE assessment in healthy participants were included in this review. Database searching revealed a total of 38 studies on EIMD and RBE in healthy participants. Three major themes of papers were identified that focused on EIMD and RBE along with (1) age related differences, (2) sex-based differences, and (3) response in athletes. Findings of this comprehensive review suggests that both EIMD and RBE are age, and sex specific. Delayed onset muscle soreness played a major role in both EIMD and RBE in all the population types. Female participants are less susceptible to EIMD as compared to age-matched male counterparts. Moreover, both EIMD and RBE are more elicited in middle aged and younger adults as compared to children and older adults while the magnitude of RBE turns out to be minimal in trained individuals due to persisting adaptations.

The Relationship Between Acute Exercise-Induced Changes in Extramuscular Connective Tissue Thickness and Delayed Onset Muscle Soreness in Healthy Participants: A Randomized Controlled Crossover Trial

Background

The extramuscular connective tissue (ECT) has been shown to play a significant role in mechanical force transmission between musculoskeletal structures. Due to this and owing to its tight connection with the underlying muscle, the ECT may be vulnerable to excessive loading. The present study aimed to investigate the effect of eccentric elbow flexor exercise on the morphology of the biceps brachii ECT. In view of the high nociceptive capacity of the ECT, an additional objective was to elucidate the potential relationship between ECT damage and the occurrence of delayed onset muscle soreness (DOMS).

Methods

Eleven healthy participants (♂ = 7; 24 ± 2 years) performed fatiguing dumbbell elbow flexor eccentric exercise (EE) for one arm and concentric exercise (CE) for the other arm in random order and with random arm allocation. Before, immediately after and 24–96 h post-exercise, maximal voluntary isometric contraction torque of the elbow flexors (dynamometer), pressure pain (algometer), palpation pain (100 mm visual analog scale), biceps brachii ECT thickness and ECT/muscle mobility during passive movement (both high-resolution ultrasound) were examined.

Results

Palpation pain, suggestive of DOMS, was greater after EE than CE, and maximal voluntary isometric contraction torque decreased greater after EE than CE (p < .05). Relative to CE, EE increased ECT thickness at 48 (+ 17%), 72 (+ 14%) and 96 (+ 15%) hours post-exercise (p < .05). At 96 h post-EE, the increase in ECT thickness correlated with palpation pain (r = .68; p < .05). ECT mobility was not different between conditions, but compared to CE, muscle displacement increased at 24 (+ 31%), 72 (+ 31%) and 96 (+ 41%) hours post-EE (p < .05).

Conclusion

Collectively, these results suggest an involvement of the ECT changes in delayed onset muscle soreness.

Circulating nitrate-nitrite reduces oxygen uptake for improving resistance exercise performance after rest time in well-trained CrossFit athletes

This study aimed to determine the effects of circulating nitrate plus nitrite (NOx) concentrations on resistance exercise performance, VO₂ and biomarkers of muscle damage. Eleven well-trained male CrossFit athletes (29.2 ± 3.7 years, 78.9 ± 5.4 kg, 175.1 ± 6.3 cm) carried out a resistance exercise test after drinking 140 mL of beetroot juice (BJ) or placebo. The test consisted of repeating the same resistance exercise routine twice: wall ball shots plus full back squat with 3-min rest (1st routine) or without rest (2nd routine) between the two exercises. Higher NO_x plasma levels were verified after BJ than placebo in the pretest and post-test (p < 0.001). A higher number of repetitions was observed after BJ intake compared to placebo in the full back squat exercise during the first routine (p = 0.004). A significantly reduced VO₂ was detected after BJ intake compared to placebo during rest and full back squat execution in the first routine (p < 0.05). Plasma myoglobin concentrations were significantly increased with BJ compared to placebo (p = 0.036). These results showed that plasma NOx levels reduced VO₂ after BJ intake during rest time. These reduced VO₂ was a key factor for improving full back squat performance during the first routine.

Changes in Insulin Sensitivity and Lipid Profile Markers Following Initial and Secondary Bouts of Multiple Eccentric Exercises

An acute bout of eccentric exercise affects insulin sensitivity and lipid profile, but how the magnitude of muscle damage affects them is not clear. We compared changes in blood insulin sensitivity and lipid markers after the first (EC1) and second (EC2) eccentric exercise bouts. Fifteen sedentary young men performed arm, leg and trunk muscle eccentric exercises, and repeated them 2 weeks later. Fasting blood samples were taken before, 2 h and 1–5 days after each exercise bout to analyze plasma creatine kinase (CK) activity, serum glucose (GLU), insulin, homeostasis model assessment (HOMA), triacylglycerols (TG), total (TC) and low- (LDLC) and high-density lipoprotein cholesterol (HDLC) concentrations as well as TC/HDLC ratio. Changes in these measures were compared between bouts and relationships to peak plasma CK activity were analyzed. Plasma CK activity increased (p < 0.05) after EC1 (peak: 101,668 ± 58,955 IU/L) but not after EC2. The magnitude of changes in GLU (peak after EC1: 26 ± 10% vs. EC2: 7 ± 6%), insulin (46 ± 27% vs. 15 ± 8%), HOMA (86 ± 48% vs. 24 ± 15%), TC (−20 ± 5% vs. −6 ± 4%), TG (−32 ± 11% vs. −6 ± 3%), LDHC (−47 ± 15% vs. −12 ± 9%), HDLC (35 ± 26% vs. 7 ± 4%), and TC/HDLC ratio (−139 ± 13% vs. −11 ± 7%) were significantly greater after EC1 than EC2. Peak plasma CK activity was significantly (p < 0.05) correlated with the peak changes in blood insulin sensitivity and lipid markers for the combined data of EC1 and EC2. These results suggest that the greater the magnitude of muscle damage, the greater the magnitude of changes in the insulin sensitivity to a negative direction and lipid markers to a positive direction.

Feasability of An Eccentric Isokinetic Protocol to Induce Trunk Muscle Damage: A Pilot Study

Eccentric exercise is discussed as a treatment option for clinical populations, but specific responses in terms of muscle damage and systemic inflammation after repeated loading of large muscle groups have not been conclusively characterized. Therefore, this study tested the feasibility of an isokinetic protocol for repeated maximum eccentric loading of the trunk muscles. Nine asymptomatic participants (5 f/4 m; 34±6 yrs; 175±13 cm; 76±17 kg) performed three isokinetic 2-minute all-out trunk strength tests (1x concentric (CON), 2x eccentric (ECC1, ECC2), 2 weeks apart; flexion/extension, 60°/s, ROM 55°). Outcomes were peak torque, torque decline, total work, and indicators of muscle damage and inflammation (over 168 h). Statistics were done using the Friedman test (Dunn’s post-test). For ECC1 and ECC2, peak torque and total work were increased and torque decline reduced compared to CON. Repeated ECC bouts yielded unaltered torque and work outcomes. Muscle damage markers were highest after ECC1 (soreness 48 h, creatine kinase 72 h; p<0.05). Their overall responses (area under the curve) were abolished post-ECC2 compared to post-ECC1 (p<0.05). Interleukin-6 was higher post-ECC1 than CON, and attenuated post-ECC2 (p>0.05). Interleukin-10 and tumor necrosis factor-α were not detectable. All markers showed high inter-individual variability. The protocol was feasible to induce muscle damage indicators after exercising a large muscle group, but the pilot results indicated only weak systemic inflammatory responses in asymptomatic adults.

Circulating Concentration of Chemical Elements During Exercise-Induced Muscle Damage and the Repeated Bout Effect

The objective of the study was to evaluate the circulating levels of chemical elements after exercise-induced muscle damage (EIMD) followed by the repeated bout effect (RBE). Seven physically active subjects (26.5 ± 4.0 years) performed two sessions of EIMD (5 sets of 20 drop jumps), the second session 14 days after the first for RBE assessment. Blood collections, countermovement jump (CMJ), squat jump (SJ), and delayed-onset muscle soreness (DOMS) were performed before (Pre), after (Post), and 24, 48, and 72 h after the exercise session. Creatine kinase (CK) was detected by biochemical analysis and the concentration of chemical elements by total reflection X-ray fluorescence (TXRF). Differences between time points and sessions were assessed with two-way ANOVA and the effect size (ES). EIMD induced a reduction in the CMJ at 24 h (P < 0.05) and an increase in DOMS at 24 h (P < 0.01) and 48 h (P < 0.01), and CK at 72 h (P < 0.05). RBE alleviated all symptoms of EIMD in the second session (P > 0.05). EIMD induced a large to very large ES for Zn reduction at 24 h (- 1.37) and 72 h (- 0.93) and Br (- 0.83) at 72 h. RBE presented large to very large ES for the increase in P at 48 h (0.92); Cl at 24 h (1.04); K at 24 h (0.91), 48 h (1.10), and 72 h (0.96); Ca at 72 h (0.92); and Fe at 24 h (0.85). RBE influenced the concentration of elements associated with fatigue (K, Ca, Cl), inflammatory response, and glucose metabolism (Zn).

Recovery from resistance exercise in older adults: a protocol for a scoping review

INTRODUCTION

Resistance exercise has been shown to improve muscle health in older adults and is recommended as a front-line treatment for many health conditions, including sarcopenia and frailty. However, despite considerable research detailing the potential benefits of resistance exercise programmes, little is known about how older adults recover from individual exercise sessions. This scoping review will examine the current evidence surrounding the acute post-exercise effects of resistance exercise and the exercise recovery process in older adults to inform future research and exercise prescription guidelines for older adults.

METHODS AND ANALYSIS

The methodological framework of Arksey and O'Malley (2005) will be applied for this scoping review. A systematic search of five online databases and the hand-searching of reference lists of identified articles will be used to identify relevant papers. Studies that aim to measure exercise-induced muscle damage or exercise recovery following a resistance exercise session in participants aged 65 years and over will be included. Qualitative and quantitative data from relevant studies will be presented in a tabular format. Results will be summarised in narrative format. Key findings will be discussed concerning resistance exercise prescription in older adults.

DISSEMINATION

This review will be used to direct further research surrounding the exercise recovery process from resistance exercise in older adults and will also aid in designing specific exercise prescription guidelines for an older population. Findings will be relevant to researchers, clinicians, health workers and policy-makers and disseminated through publications and presentations.

Biochemical Monitoring of Muscle Recovery in Elite Handball Using an Individualized Approach

Purpose: To evaluate the classification performance of a new method to individualize reference ranges for biomarkers of muscle recovery in elite handball. Methods: In a longitudinal observational study, creatine kinase (CK) and urea levels were assessed in 16 male elite handball players during the 2019–20 preseason. Blood samples were collected at prespecified time points when players were considered either recovered or nonrecovered. Initially, linear mixed-effects models were calculated, as outlined in the study design, to examine the effect of recovery status on CK and urea levels. Finally, a fixed-effect model was calculated for urea based on the law of parsimony. Individualized reference ranges were calculated using a recently published algorithm. To investigate whether the individualized approach resulted in a more accurate classification of recovery status (recovered or nonrecovered), it was compared with a group-based approach derived from the same data set, utilizing predefined error rates. Results: Linear mixed-effects models showed a large effect of recovery status on CK (P < .001, d = 3.49) and a small effect on urea (P = .018, d = 0.382). In contrast to CK (P = .017), urea had no significant interindividual variation. Hence, individualization was examined only for CK. The numerical decrease in both CK error rates by the individualized approach was significant for the test-pass error rate (P = .0196, ϕ = .19). Conclusions: Our findings underscore the critical role of CK for monitoring in team sports such as handball. The observed improvement in CK error rates suggests a promising opportunity to individualize biochemical monitoring, although further studies encompassing larger sample sizes are warranted.

Changes in blood bone markers after the first and second bouts of whole-body eccentric exercises

The present study compared the first (EC1) and second (EC2) bouts of whole-body eccentric exercises to examine the effects of the magnitude of muscle damage on changes in blood bone markers. Fifteen sedentary young men performed nine eccentric exercises of arm, leg and trunk muscles, and repeated them two weeks later. Blood samples were taken before and two hours and one to five days following each bout to analyze plasma creatine kinase (CK) activity and myoglobin concentration, serum tartrate resistant acid phosphatase (TRAP), type 1 C-terminal telopeptide (CTX-1), procollagen type I N-terminal propeptide (P1NP), bone-specific alkaline phosphatase (BAP), undercarboxylated-osteocalcin (ucOCN), carboxylated-osteocalcin (cOCN), and leptin concentrations. All except ucOCN changed significantly (P<0.05) after both bouts. When comparing bouts for peak changes, P1NP (bone formation marker) and CTX-1 (bone resorption marker) increased less after EC2 (peak: 137±96% and 7±6%, respectively) than after EC1 (146±80% and 30±21%, respectively), whereas BAP (bone formation marker) increased more after EC2 (18±16%) than after EC1 (4±15%) (P<0.05). Leptin (49±58%) and cOCN (14±10%) increased more (P<0.05) after EC2 than after EC1 (-30±15%, 9±26%). Significant (P<0.05) correlations were evident between peak CK activity and peak CTX-1 (r=0.847), P1NP (r=0.815), BAP (r=-0.707), ucOCN (r=0.627), cCON (r=-0.759) and leptin (r=-0.740) changes after EC1, but many of these correlations disappeared after EC2. This was also found for the relationships between other muscle damage markers (myoglobin, muscle soreness and muscle strength) and the bone markers. It was concluded that bone turnover was affected by eccentric exercise, but muscle damage was unfavorable for bone formation.

Effects of Resistance Training to Muscle Failure on Acute Fatigue: A Systematic Review and Meta-Analysis

BACKGROUND

Proper design of resistance training (RT) variables is a key factor to reach the maximum potential of neuromuscular adaptations. Among those variables, the use of RT performed to failure (RTF) may lead to a different magnitude of acute fatigue compared with RT not performed to failure (RTNF). The fatigue response could interfere with acute adaptive changes, in turn regulating long-term adaptations. Considering that the level of fatigue affects long-term adaptations, it is important to determine how fatigue is affected by RTF versus RTNF.

OBJECTIVE

The aim of this systematic review and meta-analysis was to compare the effects of RTF versus RTNF on acute fatigue.

METHODS

The search was conducted in January 2021 in seven databases. Only studies with a crossover design that investigated the acute biomechanical properties (vertical jump height, velocity of movement, power output, or isometric strength), metabolic response (lactate or ammonia concentration), muscle damage (creatine kinase activity), and rating of perceived exertion (RPE) were selected. The data (mean ± standard deviation and sample size) were extracted from the included studies and were either converted into the standardized mean difference (SMD) or maintained in the raw mean difference (RMD) when the studies reported the results in the same scale. Random-effects meta-analyses were performed.

RESULTS

Twenty studies were included in the systematic review and 12 were included in the meta-analysis. The main meta-analyses indicated greater decrease of biomechanical properties for RTF compared with RTNF (SMD - 0.96, 95% confidence interval [CI] - 1.43 to - 0.49, p < 0.001). Furthermore, there was a larger increase in metabolic response (RMD 4.48 mmol·L^-1, 95% CI 3.19-5.78, p < 0.001), muscle damage (SMD 0.76, 95% CI 0.31-1.21, p = 0.001), and RPE (SMD 1.93, 95% CI 0.87-3.00, p < 0.001) for RTF compared with RTNF. Further exploratory subgroup analyses showed that training status (p = 0.92), timepoint (p = 0.89), load (p = 0.10), and volume (p = 0.12) did not affect biomechanical properties; however, greater loss in the movement velocity test occurred on upper limbs compared with lower limbs (p < 0.001). Blood ammonia concentration was greater after RTF than RTNF (RMD 44.66 μmol·L^-1, 95% CI 32.27-57.05, p < 0.001), as was 48 h post-exercise blood creatine kinase activity (SMD 0.86, 95% CI 0.33-1.42, p = 0.002). Furthermore, although there was considerable heterogeneity in the overall analysis (I² = 83.72%; p < 0.01), a significant difference in RPE after RTF compared with RTNF was only found for studies that did not equalize training volumes.

CONCLUSIONS

In summary, RTF compared with RTNF led to a greater decrease in biomechanical properties and a simultaneous increase in metabolic response, higher muscle damage, and RPE. The exploratory analyses suggested a greater impairment in the velocity of movement test for the upper limbs, more pronounced muscle damage 48 h post-exercise, and a greater RPE in studies with non-equalized volume after the RTF session compared with RTNF. Therefore, it can be concluded that RTF leads to greater acute fatigue compared with RTNF. The higher acute fatigue after RTF can also have an important impact on chronic adaptive processes following RT; however, the greater acute fatigue following RTF can extend the time needed for recovery, which should be considered when RTF is used.

PROTOCOL REGISTRATION

The original protocol was prospectively registered (CRD42020192336) in the International Prospective Register of Systematic Reviews (PROSPERO).

Effect of repeated eccentric exercise on muscle damage markers and motor unit control strategies in arm and hand muscle

To examine the contralateral repeated bout effect (CL-RBE) on muscle damage markers and motor unit (MU) control strategies, seventeen healthy adults performed two bouts of 60 eccentric contractions with elbow flexor (EF group; n ​= ​9) or index finger abductor (IA group; n ​= ​8) muscles, separated by 1 week. All participants randomly performed eccentric exercise on either the right or left arm or hand muscles, and muscle damage markers and submaximal trapezoid contraction tests were conducted pre, post, 1- and 2-day post eccentric protocol. One week after the first bout, the same exercise protocol and measurements were performed on the contralateral muscles. Surface electromyographic (EMG) signals were collected from biceps brachii (BB) or first dorsal interosseous (FDI) during maximal and submaximal tests. The linear regression analyses were used to examine MU recruitment threshold versus mean firing rate and recruitment threshold versus derecruitment threshold relationships. EMG amplitude from BB (bout 1 vs. bout 2 ​= ​65.71% ​± ​22.92% vs. 43.05% ​± ​18.97%, p ​= ​0.015, d ​= ​1.077) and the y-intercept (group merged) from the MU recruitment threshold versus derecruitment threshold relationship (bout 1 vs. bout 2 ​= ​−7.10 ​± ​14.20 vs. 0.73 ​± ​16.24, p ​= ​0.029, d ​= ​0.513) at 50% MVIC were significantly different between two bouts. However, other muscle damage markers did not show any CL-RBE in both muscle groups. Therefore, despite changes in muscle excitation and MU firing behavior, our results do not support the existence of CL-RBE on BB and FDI muscles.

Eccentric exercise causes delayed sensory nerve conduction velocity but no repeated bout effect in the flexor pollicis brevis muscles

PURPOSE

This study was aimed at investigating the effect of eccentric contractions (ECCs) of flexor pollicis brevis muscles (FPBMs) on motor and sensory nerve functions as well as the ipsilateral repeated bout effect (IL-RBE) and contralateral (CL)-RBE of motor and sensory nerve conduction velocities following ECCs.

METHODS

Thirty-two young healthy men (age: 19.6 ± 0.2 years, height: 173.2 ± 1.2 cm, body mass: 69.7 ± 1.9 kg) performed two bouts of ECCs. During the first ECCs bout (ECCs-1), all participants performed 100 ECCs with 1 hand; for the second bout, 3 groups (2 weeks [W]: n = 11, 4W: n = 10, 8W: n = 11) performed ECCs with both hands 2, 4, or 8 weeks after ECCs-1. The maximal voluntary isometric contraction (MVC), range of motion (ROM), visual analog scale for pain (VAS), motor and sensory nerve conduction velocities were measured before, immediately after, and 1, 2, 3, and 5 days after ECCs.

RESULTS

ECCs-1 decreased the MVC, limited the ROM, developed VAS, and decreased the motor and sensory nerve conduction velocities compared to non-exercise hand (p < 0.05). The repeated bout effect was observed in the ROM for IL-RBE in 2W and 4W, VAS for IL-RBE in 2 W, and ROM and VAS for CL-RBE in 2W (p < 0.05). However, RBEs of MVC and motor and sensory nerve conduction velocities were not observed, and no differences were confirmed depending on the interval.

CONCLUSION

In the present study, ECCs of the FPBM caused a sensory nerve dysfunction, while IL- or CL-RBE was not observed.

The Effects of Cannabidiol Oil on Noninvasive Measures of Muscle Damage in Men

PURPOSE

This study aimed to investigate the effect of CBD oil on perceived muscle soreness, inflammation, and strength performance after eccentric exercise (ECC) of the elbow flexors.

METHODS

Thirteen untrained men (mean ± SD age, 21.85 ± 2.73 yr) performed 6 sets of 10 maximal ECC isokinetic muscle actions of the elbow flexors as part of a double-blind crossover design. Noninvasive (perceived soreness, arm circumference, hanging joint angle (JA), and peak torque (PT)) measures were taken before and after ECC, and 24, 48, and 72 h after ECC. All subjects completed both the supplement (CBD: 150 mg POST, 24 h, 48 h) and placebo (PLC: POST, 24 h, 48 h) condition separated by 2 wk. Four separate two-way repeated-measures ANOVA (condition [CBD vs PLC] × time [PRE vs POST vs 24 h vs 48 h vs 72 h]) were used to analyze perceived soreness, arm circumference, JA, and PT. One-way repeated-measures ANOVA were used to decompose significant interactions and main effects.

RESULTS

There was no condition-time interaction or main effect of condition (P > 0.05) for perceived soreness, arm circumference, JA, or PT. There were main effects for time for perceived soreness (P = 0.000, ηp2 = 0.71) and JA (P = 0.006, ηp2 = 0.35).

CONCLUSIONS

The current dose of 150 mg CBD oil at POST, 24 h, and 48 h had no effect on noninvasive markers of muscle damage in the upper extremity. At the current dose and schedule, CBD oil may not be beneficial for untrained men as a recovery aid after exercise-induced muscle damage.

Response of Knee Extensor Muscle-Tendon Unit Stiffness to Unaccustomed and Repeated High-Volume Eccentric Exercise

The purposes of this study were to investigate the muscle-tendon unit stiffness response and to compare the stiffness with those of other indirect markers induced by two bouts of unaccustomed eccentric exercise. Eleven untrained men performed two bouts of 200 maximal eccentric contractions of the right quadriceps 4 weeks apart. Changes in stiffness, pain evoked by stretching and pressure, plasma creatine kinase (CK) activity, and muscle thickness were followed for 7 days after each bout. Stiffness and pain peaked immediately and 1 day after the first exercise bout, whereas CK and thickness were highest 4 and 7 days after the first exercise bout, respectively (p < 0.05 for all). Muscular pain, thickness, and stiffness responses were lower by 53.3%, 99%, and 11.6%, respectively, after the repeated bout compared to after the first bout (p < 0.05 for all), while CK activity response did not differ significantly between bouts. High responders for an increase in muscle-tendon unit stiffness showed a repeated-bout effect for stiffness, pain, and CK activity (by 29%, 65%, and 98%, p < 0.05 for all), but the repeated-bout effect was not that clear in low responders. These findings suggest that a repeated eccentric exercise bout effect on stiffness in quadriceps is mostly not associated with muscle pain and CK activity, but there are large individual differences.

Acute Inflammatory, Cortisol, and Soreness Responses to Supramaximal Accentuated Eccentric Loading

ABSTRACT

Merrigan, JJ and Jones, MT. Acute inflammatory, cortisol, and soreness responses to supramaximal accentuated eccentric loading. J Strength Cond Res 35(2S): S107-S113, 2021-The purpose was to determine differences in time under tension, cortisol, inflammation, and perceived soreness between accentuated eccentric (AEL) and traditional loading (TRA) resistance exercise protocols. Resistance-trained men (n = 21) completed the AEL and TRA protocols in a random order, separated by 48 hours (sets × reps at eccentric/concentric) as follows: AEL65, 3 × 5 at 120/65% 1 repetition maximum (RM); AEL80, 3 × 3 at 120/80% 1RM; TRA65, 3 × 5 at 65/65% 1RM; and TRA80, 3 × 3 at 80/80% 1RM. Four linear position transducers measured eccentric time under tension (ETUT) and total time under tension (TTUT). Ultrasonography measured vastus lateralis muscle thickness and echo intensity at baseline and immediately post-exercise. Salivary cortisol was assessed at baseline, 0-, 15-, 30-, and 60-minute post-exercise. Perceived soreness was assessed at baseline, 24-, and 48-hours post-exercise. During rep 1, AEL65 and AEL80 had longer ETUT and TTUT than TRA65 (p ≤ 0.002) and TRA80 (p ≤ 0.008), respectively. However, AEL65 had shorter ETUT (reps 3-5) and TTUT (reps 3-5) than TRA65 (p ≤ 0.043). Similarly, ETUT (reps 2-3) and TTUT (rep 3) was shorter in AEL80 than TRA80 (p ≤ 0.045). However, there was no protocol effect for ETUT and TTUT (p > 0.05). Muscle thickness changes were trivial after each protocol (AEL80, d = 0.19; TRA80, d = 0.15; AEL65, d = 0.24; TRA65, d = 0.23), but changes in echo intensity were moderate (AEL80, d = 0.61; TRA80, d = 0.61; AEL65, d = 0.61; TRA65, d = 0.76). Salivary cortisol decreased below baseline at 30- and 60-minute post-exercise (p ≤ 0.006). Perceived soreness elevated from baseline to 24 hours for AEL80 (p = 0.006). The inflammatory, cortisol, and soreness responses after AEL were either low or similar to TRA, indicating similar recovery patterns between protocols.

Effect of Arm Eccentric Exercise on Muscle Damage of the Knee Flexors After High-Intensity Eccentric Exercise

Repeated bout effect (RBE) describes a phenomenon that an initial unaccustomed eccentric exercise (ECC) bout can confer a protective effect against muscle damage from the subsequent same exercise. This protection has been observed in the same muscle, as well as the contralateral homologous (CL-RBE) muscle. But it is unknown whether the RBE is evident for non-local unrelated heterogonous muscles. The purpose of this study was to examine whether an initial elbow flexion (EF) muscle-damaging ECC could confer RBE against muscle damage from the subsequent ECC performed in the remote lower limb knee flexor (KF) muscle group. Twenty-seven young individuals were randomly assigned into the experimental (EXP: n = 15) and the control (CON: n = 12) groups. All participants performed a baseline unilateral KF ECC (six sets of 10 repetitions) on a randomly chosen leg. After a washout period (4 weeks), the EXP group performed 60 high-intensity unilateral EF ECC on a randomly chosen arm, followed by the same intensity exercise using the contralateral KF muscle group 2 weeks later. The CON group performed the same contralateral KF ECC, but with no prior EF ECC bout. Changes in the KF muscle damage indirect markers (muscle soreness, range of motion, and maximal isometric strength) after the ECC were compared between the baseline and second bouts for both groups with mixed factorial three-way (group × bout × time) ANOVA. Additionally, index of protection for each damage marker was calculated at 1 and 2 days after the ECC and compared between groups with independent t-tests. For both groups, the magnitude of the changes in the damage markers between the baseline and the second ECC bouts were not significantly different (all values of p > 0.05). As for the index of protection, relative to the CON, the EXP showed an exacerbating damaging effect on the KF isometric strength following the second ECC bout, particularly at the 1-day post-exercise time point (index of protection: EXP vs. CON mean ± SD = -29.36 ± 29.21 vs. 55.28 ± 23.83%, p = 0.040). Therefore, our results do not support the existence of non-local RBE.

Elevation of fast but not slow troponin I in the circulation of patients with Becker and Duchenne muscular dystrophy

Introduction

One of the hallmarks of injured skeletal muscle is the appearance of elevated skeletal muscle proteins in circulation. Human skeletal muscle generally consists of a mosaic of slow (type I) and fast (type IIa, IIx/d) fibers, defined by their myosin isoform expression. Recently, measurement of circulating fiber‐type specific isoforms of troponin I has been used as a biomarker to suggest that muscle injury in healthy volunteers (HV) results in the appearance of muscle proteins from fast but not slow fibers. We sought to understand if this is also the case in severe myopathy patients with Becker and Duchenne muscular dystrophy (BMD, DMD).

Methods

An enzyme‐linked immunosorbent assay (ELISA) that selectively measures fast and slow skeletal troponin I (TNNI2 and TNNI1) was used to measure a cross‐section of patient plasma samples from HV (N = 50), BMD (N = 49), and DMD (N = 132) patients. Creatine kinase (CK) activity was also measured from the same samples for comparison.

Results

TNNI2 was elevated in BMD and DMD and correlated with the injury biomarker, CK. In contrast, TNNI1 levels were indistinguishable from levels in HV. There was an inverse relationship between CK and TNNI2 levels and age, but no relationship for TNNI1.

Discussion

We define a surprising discrepancy between TNNI1 and TNNI2 in patient plasma that may have implications for the interpretation of elevated muscle protein levels in dystrophinopathies.

See Editorial on pages 4–5 in this issue.

Striking muscle adaptations induced by volume-dependent repeated bouts of low-intensity eccentric exercise of the elbow flexors

We investigated the effects of repeating 30 low-intensity eccentric contractions with a dumbbell corresponding to 10% maximal isometric strength (10%EC) on muscle strength and hypertrophy, and muscle damage after 30 maximal eccentric contractions (MaxEC) of the elbow flexors. Young men were placed into 1 of 3 experimental groups that performed 10%EC either once, twice a week for 4 (8 bouts) or 8 weeks (16 bouts) before MaxEC, or a control group that performed 2 bouts of MaxEC separated by 2 weeks (n = 13/group). Repeating 16 bouts of 10%EC increased (P < 0.05) maximal voluntary contraction strength (30 ± 21%) and muscle thickness (4.2 ± 2.3%) greater than 8 bouts (16 ± 4%, 1.9 ± 1.3%). Changes in the muscle damage markers after MaxEC were smaller (P < 0.05) for the experimental groups than the control group, and the magnitude of muscle damage protection was greater (P < 0.05) after 16 bouts (65 ± 30%) than 8 bouts (55 ± 33%), followed by 1 bout (34 ± 27%). The protection by 16 bouts was similar (P = 0.81) to that shown by the second MaxEC of the control group. These results showed that 10%EC produced potent muscle adaptation effects accumulatively and conferred muscle damage protection, but 1 bout of 10%EC was still effective for conferring approximately 20% of the protection of that by 16 bouts. Novelty: Repeating low-intensity eccentric exercise induces large increases in muscle strength and hypertrophy. Low-intensity eccentric exercise protects muscle damage induced by maximal eccentric contractions, and the protection is reinforced by repeating it. These are especially beneficial for individuals who are frail and cannot tolerate high-intensity resistance training.

Effects of wrist position on eccentric exercise-induced muscle damage of the elbow flexors

We tested the hypothesis that the magnitude of changes in indirect muscle damage markers would be greater after maximal elbow flexor eccentric exercise in the supinated (shorter biceps brachii) than neutral wrist (longer) position, and the difference in the magnitude would be associated with greater elongation over contractions for the supinated than neutral position, rather than the initial muscle length. Ten untrained men (21-39 years) performed two bouts of 10 sets of 6 maximal isokinetic eccentric contractions of the elbow flexors in the supinated position for one arm and neutral position for the other arm separated by 2 weeks in a randomized order. Biceps brachii myotendinous junction (MTJ) movements during eccentric contractions were recorded by B-mode ultrasonography, and the displacement from the start to end of each contraction was quantified. Peak torque (supinated: 367.8 ± 112.5 Nm, neutral: 381.5 ± 120.4 Nm) and total work (1816 ± 539 J, 1865 ± 673 J) produced during eccentric contractions were similar between conditions. The average MTJ displacement increased (P < .05) from the 1st set (8.0 ± 2.0 mm) to 10th set (15.8 ± 1.9 mm) for the supinated condition, but no such increase was found in the neutral condition (1st set: 5.1 ± 1.0 mm, 10th set: 5.0 ± 0.8 mm). Changes in indirect muscle damage markers (maximal voluntary isometric contraction torque, range of motion, serum creatine kinase activity, and muscle soreness) after exercise were greater (P < .05) for the supinated than neutral condition. These results suggest that the greater muscle damage marker changes for the supinated than neutral wrist position was associated with the greater muscle lengthening (strain).

Survey of Eccentric-Based Strength and Conditioning Practices in Sport

McNeill, C, Beaven, CM, McMaster, DT, and Gill, N. Survey of eccentric-based strength and conditioning practices in sport. J Strength Cond Res 34(10): 2769-2775, 2020-Eccentric-based training (ECC) has been shown to be an effective training strategy in athletes; however, despite the theoretical benefits, the uptake by practitioners is currently unknown. This study investigated the current ECC strength and conditioning practices that are implemented in the training of athletes. Two hundred twenty-four practitioners were electronically surveyed anonymously with 98 responses available for analysis. Nearly all respondents (96%) had prescribed ECC in the last 24 months. Sport performance (64%), injury prevention (24%), and rehabilitation (8%) were the top-ranked reasons to include ECC. Respondents programmed ECC for strength (35%), hypertrophy (19%), and power (18%). A majority of respondents did not monitor ECC load (58%) or use eccentric-specific testing (75%). Seventeen respondents commented that high-intensity training such as sprinting and change of direction, were avoided during ECC blocks. Eccentric-based training intensity was prescribed as percentage of 1 repetition maximum (34%), rate of perceived exertion (20%), or velocity (16%). Respondents indicated muscle soreness and concurrent high-intensity activities were concerns during ECC but reported not using eccentric monitoring or testing. The efficacy of ECC is well supported, yet there seems to be a lack of defined protocol for integrating ECC research into practice. A greater understanding of eccentric contribution to sport performance and injury prevention may help define testing and monitoring procedures for the prescription of ECC interventions. Practitioners should consider factors such as periodization, soreness, and monitoring when designing ECC programs. The findings of this survey indicate that no uniform strategies exist for the prescription of ECC among experienced practitioners.

Regional changes in muscle activity do not underlie the repeated bout effect in the human gastrocnemius muscle

The repeated bout effect (RBE) confers protection following exercise-induced muscle damage. Typical signs of this protective effect are significantly less muscle soreness and faster recovery of strength after the second bout. The aim of this study was to compare regional changes in medial gastrocnemius (MG) muscle activity and mechanical hyperalgesia after repeated bouts of eccentric exercise. Twelve healthy male participants performed two bouts of eccentric heel drop exercise (separated by 7 days) while wearing a vest equivalent to 20% of their body weight. High-density MG electromyographic amplitude maps and topographical pressure pain sensitivity maps were created before, two hours (2H), and two days (2D) after both exercise bouts. Statistical parametric mapping was used to identify RBE effects on muscle activity and mechanical hyperalgesia, using pixel-level statistics when comparing maps. The results revealed a RBE, as a lower strength loss (17% less; P < .01) and less soreness (50% less; P < .01) were found after the second bout. However, different muscle regions were activated 2H and 2D after the initial bout but not following the repeated bout. Further, no overall changes in EMG distribution or mechanical hyperalgesia were found between bouts. These results indicate that muscle activation is unevenly distributed during the initial bout, possibly to maintain muscle function during localized mechanical fatigue. However, this does not reflect a strategy to confer protection during the repeated bout by activating undamaged/non-fatigued muscle areas.

Technical match actions and plasma stress markers in elite female football players during an official FIFA Tournament

This study analyzed the impact of performing four consecutive football matches separated by 48-72 hours during a FIFA tournament on physical load, technical performance and plasma markers of redox state, muscle damage and inflammation in elite female players. Forty-eight players from three national teams were evaluated at seven time points: before (baseline) and throughout the tournament (after each match and before two training sessions). Only data from players who played all matches were included in the analyses (N = 13). The players were divided into high-rank (N = 6) and low-rank (N = 7) team players according to FIFA standards. Plasma creatine kinase (CK), C-reactive protein (CRP), total antioxidant status (TAS), and uric acid (UA) were analyzed at the selected time points. Technical performance and physical load were also quantified according to team rank. Players from low-rank teams played significantly more time than high-rank players (85 ± 10 vs 67 ± 15 minutes; P = .02; d = 1.51). Low-rank team players presented higher values in technical performance actions than the high-rank team players, but most of the differences were explained by the longer match time played. UA content differed across the matches, increasing from baseline (F_(4,40)  = 3.90; P = .01) and more in the high-rank team players (F_(1,10)  = 20.46; P = .001), while CRP only differed across the matches (F_(4,36)  = 2.66; P = .05), also increasing from baseline. A large time effect was shown for UA only in the high-rank players (η² _p  = 0.50; P = .02). Four consecutive matches did not result in considerable alterations in plasma stress markers, physical load, and technical performance in elite female football players from distinct rank levels.

Effect of preconditioning exercise on biceps brachii myotendinous junction displacement during elbow flexor eccentric exercise

The present study tested the hypothesis that 30 low-intensity (10%) eccentric contractions (10%EC) or two maximal voluntary isometric contractions at a long muscle length (2MVIC) that were performed at two days before maximal eccentric exercise of the elbow flexors consisting of five sets of six maximal eccentric contractions (MaxEC) would reduce increases in biceps brachii distal myotendinous junction displacement (MTJd) over the eccentric contractions during MaxEC. Sedentary young men were randomly placed (n = 12/group) to a control group that performed two bouts of MaxEC (CONT-1st, CONT-2nd) separated by two weeks, or one of two preconditioning groups that performed 10%EC or 2MVIC at 20° elbow flexion at two days prior to MaxEC. All exercises were performed by the non-dominant arm. MTJd of each contraction was assessed by B-mode ultrasound, and its changes over sets were compared among the groups. The average MTJd from the start to the end of six eccentric contractions in the first set was similar among the groups (6.4 ± 0.7 mm). The MTJd increased from the first to fifth set, but the increase was smaller (P < .05) for the 10%EC (13 ± 6%) and 2MVIC (16 ± 9%) groups, and CONT-2nd (3 ± 6%) when compared with CONT-1st (60 ± 12%). Both 10%EC and 2MVIC groups showed smaller (P < .05) changes in all muscle damage markers after MaxEC similarly when compared with CONT-1st, but the changes were greater than those after CONT-2nd. These results supported the hypothesis that protective effect was associated with less MTJd changes, suggesting that this is associated with the mechanisms underpinning the preconditioning effect on muscle damage.

The Effects of a Preconditioning Rolling Session on Subsequent Eccentric Exercise-Induced Muscle Damage

West, JT, Miller, WM, Jeon, S, and Ye, X. The effects of a preconditioning rolling session on subsequent eccentric exercise-induced muscle damage. J Strength Cond Res 34(8): 2112-2119, 2020-The aim of this study was to examine the effects of a preexercise unilateral quadriceps muscle rolling intervention on subsequent ipsilateral (IPSI) or contralateral (CTRA) knee extension eccentric exercise-induced muscle damage. Twenty-seven healthy volunteers (14 men) underwent an eccentric exercise protocol (6 sets of 10 repetitions with 75% of the maximal isometric strength) with a single-leg knee extension machine. Before the eccentric exercise, the subjects were randomly assigned to either (a) IPSI group: rolling the ipsilateral knee extensor muscles, (b) CTRA: rolling the contralateral muscles, or (c) Control: sitting for 6 minutes (same duration as the rolling intervention protocol) relaxed. The muscle soreness, passive knee extension range of motion, and knee extension isometric strength were measured before, immediately, 24 hours, and 48 hours after exercise. The magnitudes of the range of motion decrement were attenuated in both the IPSI (p = 0.031) and CTRA (p = 0.014) groups 24 hours after the eccentric exercise, when compared with the control. Isometric strength (p = 0.783) and muscle soreness (p = 0.586) responses were not significantly different among the 3 groups (time points and sexes merged). Additionally, women displayed an overall faster recovery than men in isometric strength (p = 0.001) and muscle soreness (p = 0.024), evidenced by the measurements at 48 hours after exercise. Our study suggests that unilateral quadriceps rolling intervention before high-intensity muscle-damaging exercise has a beneficial effect on maintaining range of motion in both the ipsilateral and contralateral muscles.

Aging and Recovery After Resistance-Exercise-Induced Muscle Damage: Current Evidence and Implications for Future Research

Aging is anecdotally associated with a prolonged recovery from resistance training, though current literature remains equivocal. This brief review considers the effects of resistance training on indirect markers of muscle damage and recovery (i.e., muscle soreness, blood markers, and muscle strength) in older males. With no date restrictions, four databases were searched for articles relating to aging, muscle damage, and recovery. Data from 11 studies were extracted for review. Of these, four reported worse symptoms in older compared with younger populations, while two have observed the opposite, and the remaining studies (n = 6) proposed no differences between age groups. It appears that resistance training can be practiced in older populations without concern for impaired recovery. To improve current knowledge, researchers are urged to utilize more ecologically valid muscle-damaging bouts and investigate the mechanisms which underpin the recovery of muscle soreness and strength after exercise in older populations.

Effects of descending or ascending stair exercise on body composition, insulin sensitivity, and inflammatory markers in young Chinese women with obesity: A randomized controlled trial

We examined the effects of descending (DSE) or ascending (ASE) stair exercise on body composition, insulin sensitivity, and inflammatory markers in young Chinese women with obesity. Thirty-six participants were randomly assigned into three groups DSE, ASE and a control group. The DSE and ASE groups performed three sessions of stair walking per week for 12 weeks with a gradual increase in repetitions. Following the exercise interventions, body composition related variables obtained by Dual-energy X-ray absorptiometry scans significantly decreased. Abdominal fat decreased in the DSE group only. Moreover, Insulin sensitivity improved significantly 3.5-fold in the DSE group compared with ASE group (insulin: -33.2% vs. -9.8%, homoeostasis model assessment for insulin resistance: -35.6% vs. -10.8%). Pro-inflammatory factors showed significant decreases in tumour necrosis factor-α (TNF-α) (-39.9% vs. -23.2%) for both intervention groups. The reduction in TNF-α concentrations in the DSE group was significantly different compared to the other two groups. Interleukin-6 significantly decreased in both exercise protocols. Our results show that 12-weeks induced stair walking improved body composition parameters in Chinese females with obesity. The results also demonstrate the superiority of the DSE protocol for improving insulin sensitivity. These findings may be attributable to the decreases observed in TNF- α levels.

A strength-oriented exercise session required more recovery time than a power-oriented exercise session with equal work

The present randomized cross-over controlled study aimed to compare the rate of recovery from a strength-oriented exercise session vs. a power-oriented session with equal work. Sixteen strength-trained individuals conducted one strength-oriented session (five repetitions maximum (RM)) and one power-oriented session (50% of 5RM) in randomized order. Squat jump (SJ), countermovement jump (CMJ), 20-m sprint, and squat and bench press peak power and estimated 1RMs were combined with measures of rate of perceived exertion (RPE) and perceived recovery status (PRS), before, immediately after and 24 and 48 h after exercise. Both sessions induced trivial to moderate performance decrements in all variables. Small reductions in CMJ height were observed immediately after both the strength-oriented session (7 ± 6%) and power-oriented session (5 ± 5%). Between 24 and 48 h after both sessions CMJ and SJ heights and 20 m sprint were back to baseline. However, in contrast to the power-oriented session, recovery was not complete 48 h after the strength-oriented session, as indicated by greater impairments in CMJ eccentric and concentric peak forces, SJ rate of force development (RFD) and squat peak power. In agreement with the objective performance measurements, RPE and PRS ratings demonstrated that the strength-oriented session was experienced more strenuous than the power-oriented session. However, these subjective measurements agreed poorly with performance measurements at the individual level. In conclusion, we observed a larger degree of neuromuscular impairment and longer recovery times after a strength-oriented session than after a power-oriented session with equal total work, measured by both objective and subjective assessments. Nonetheless, most differences were small or trivial after either session. It appears necessary to combine several tests and within-test analyses (e.g., CMJ height, power and force) to reveal such differences. Objective and subjective assessments of fatigue and recovery cannot be used interchangeably; rather they should be combined to give a meaningful status for an individual in the days after a resistance exercise session.