Eccentric exercises have been used in physical training, injury prevention, and rehabilitation programs. The systematic use of eccentric training promotes specific morphological adaptations on ...skeletal muscles. However, synergistic muscles, such as the triceps surae components, might display different structural adaptations due to differences in architecture, function, and load sharing. Therefore, the purpose of this study was to determine the effects of an eccentric training program on the triceps surae (GM, gastrocnemius medialis; GL, gastrocnemius lateralis; and SO, soleus) muscle architecture.
Twenty healthy male subjects (26 ± 4 years) underwent a 4-week control period followed by a 12-week eccentric training program. Muscle architecture fascicle length (FL), pennation angle (PA), and muscle thickness (MT) of GM, GL, and SO was evaluated every 4 weeks by ultrasonography.
Fascicle lengths (GM: 13.2%; GL: 8.8%; SO: 21%) and ML increased (GM: 14.9%; GL: 15.3%; SO: 19.1%) from pre- to post-training, whereas PAs remained similar. GM and SO FL and MT increased up to the 8th training week, whereas GL, FL increased up to the 4th week. SO displayed the highest, and GL the smallest gains in FL post-training.
All three synergistic plantar flexor muscles increased FL and MT with eccentric training. MT increased similarly among the synergistic muscles, while the muscle with the shortest FL at baseline (SO) showed the greatest increase in FL.
To compare biceps femoris long head (BFlh) muscle tendon unit and fascicle function during Nordic hamstring exercise (NHE) variations with different hip range of motion.
Cross-sectional.
Twelve ...healthy volunteers (age: 24 ± 4 years; mass: 77 ± 6 kg; height: 177 ± 4 cm) performed two NHE variations: NHE with hips in neutral (fixed) position (conventional NHE); and NHE with hip flexion/extension. BFlh fascicle length behaviour was assessed using a dual transducer ultrasound configuration. BFlh and semitendinosus muscle electromyography, lower limb kinematics and knee flexion moment were also recorded. A biomechanical model was used to estimate BFlh muscle-tendon unit (MTU) length. Statistical Parametric Mapping was used to assess timing differences in outcome variables across the movement.
In both variations, during much of the exercise (~30–80% of movement phase), BFlh fascicles undergo little length change (isometric) while the MTU lengthens. Fascicles stretched considerably just in the last ~20% of the exercise, and changes in fascicle length (<2 cm stretch) were smaller in comparison to changes in MTU length (<4 cm stretch). Hip flexion resulted in the muscle tendon unit and fascicles operating at longer lengths until approximately 80% of the movement phase.
The decoupling between fascicle and MTU length seen during the NHE variations suggests that stretch of the elastic tissue of the MTU has an important role in absorbing energy during Nordic hamstring exercises. This may be important when considering adaptations to BFlh muscle and connective tissues that might occur from NHE training.
Manipulating resistance training program variables is a commonly used tool for optimizing maximum muscle strength in rehabilitation and/or exercise training programs. The current study purposed to ...compare the effects of 12 weeks of concentric and eccentric resistance training on neuromuscular adaptation of quadriceps muscle. Methods Twenty-six male subjects (age, mean ± SD, 22.1 ± 2.4 yr; body mass, 72.3 ± 9.9 kg; height, 1.75 ± 0.08 m) were recruited for this controlled laboratory study. Subjects were randomly divided into two groups: the eccentric training group (No = 13) and the concentric training group (No = 13). The maximal isometric voluntary contraction (MVIC) of quadriceps muscles, vertical jumping, and surface electromyography (EMG) signals were recorded before and after 12 weeks of resistance concentric and eccentric training. Repeated-measures Analysis of Variance (ANOVA) was used to test differences between means before and after resistance training. Results The maximal isometric voluntary contraction of the quadriceps muscle and vertical jumping were significantly increased after eccentric and concentric training (p <0.05). Eccentric exercise resulted in a greater increase in maximal isometric voluntary contraction of the quadriceps muscle and vertical jumping compared to concentric training (p <0.05). The amplitude of surface EMG signals was also significantly increased after eccentric and concentric training (p <0.05), with a greater increase observed in the eccentric than the concentric training group (p <0.05). Conclusion The results of this study showed higher increases in muscle force output and EMG activity after eccentric training. This may indicate that stretch combined with overloading is the most effective stimulus for enhancing neuromuscular activity during dynamic resistance exercise. The knowledge gained from this study may be relevant for designing exercise and/or rehabilitation training to improve muscle output.
The aim of the current review is to discuss applications and mechanism of eccentric exercise in training regimes of competitive sports. Eccentric muscle work is important in most sports. Eccentric ...muscle contractions enhance the performance during the concentric phase of stretch-shortening cycles, which is important in disciplines like sprinting, jumping, throwing, and running. Muscles activated during lengthening movements can also function as shock absorbers, to decelerate during landing tasks or to precisely deal with high external loading in sports like alpine skiing. The few studies available on trained subjects reveal that eccentric training can further enhance maximal muscle strength and power. It can further optimize muscle length for maximal tension development at a greater degree of extension, and has potential to improve muscle coordination during eccentric tasks. In skeletal muscles, these functional adaptations are based on increases in muscle mass, fascicle length, number of sarcomeres, and cross-sectional area of type II fibers. Identified modalities for eccentric loading in athletic populations involve classical isotonic exercises, accentuated jumping exercises, eccentric overloading exercises, and eccentric cycle ergometry. We conclude that eccentric exercise offers a promising training modality to enhance performance and to prevent injuries in athletes. However, further research is necessary to better understand how the neuromuscular system adapts to eccentric loading in athletes.
The aim of this study was to investigate the value of magnetic resonance (MR) quantitative analysis (MR-T2 mapping technique) for the evaluation of eccentric exercise-induced skeletal muscle injury.
...We established an animal model of eccentric exercise-induced damage of Sprague Dawley rat skeletal muscle and evaluated the animals by MR imaging, determined the serum levels of fast skeletal troponin (fsTnI), and examined muscle histopathology, at 0, 1, 2, 4, and 7 days after eccentric exercise. The associations between MR imaging findings, and histopathological and laboratory results were evaluated.
T2-weighted images (WIs) of quadriceps femoris muscles showed obvious high signal intensities after exercise, and the T2 values and serum fsTnI levels continued to increase, peaking at day 2 after exercise, p< 0.05. The histopathological findings in muscle specimens, which included swollen and ruptured cells, enlarged extracellular spaces, inflammation, and regeneration of muscle fibers, showed similar trends. After day 2, muscle specimens began to show evidence of self-repair, the T2WI signals decreased in intensity, and the T2 values and serum fsTnI levels decreased; however, at day 7 post injury, the values remained slightly higher than those in the control animals, p< 0.05. The T2 value was significantly correlated with the serum fsTnI level (r = 0.896, p< 0.01).
T2 mapping technology accurately reflects the histopathological and fsTnI abnormalities and the degree of skeletal muscle damage associated with eccentric exercise followed by recovery. Because T2 mapping technology is noninvasive and can be quantitatively analyzed, it might become the preferred method for performing the diagnosis of eccentric exercise-induced skeletal muscle injury.
The purpose of this study was to investigate if exertional rhabdomyolysis induced by an acute bout of plyometric exercise in untrained individuals was associated with histological characteristics of ...skeletal muscle, creatine kinase (CK) polymorphism or secondary damage. Twenty-six healthy male untrained individuals completed a bout of plyometric exercise (10 sets of 10 maximal squat jumps, with each standardized to achieve at least 95% of individual maximal jump height). Blood samples were taken, and perceived pain was scored immediately before the exercise intervention and 6 h, 1, 2, and 3 days post-intervention. Muscle biopsies were collected 9 or 4 days before (baseline) and 3 days after plyometric jumps. Subjects were divided into two groups, high (
= 10) and low responders (
= 16), based on a cut-off limit for exertional rhabdomyolysis of peak CK activity ≥ 1000 U/L in any post-exercise blood sample. Perceived pain was more severe assessed in squat than standing position. Low responders perceived more pain at 6 h and 1 day, while high responders perceived more pain than low responders on days three and four after exercise; structural (dystrophin staining) and ultra-structural (transmission electron microscopy) analysis of muscle fibers revealed no baseline pathology; damage was evident in all individuals in both groups, with no difference between high and low responders in either damage or fiber type proportion. High responders had significantly higher total white blood cell and neutrophil counts 6 h and significantly higher C-reactive protein (CRP) 6 h and days one and two after exercise compared to low responders. High responders had significantly greater muscle myeloperoxidase (MPO) levels in baseline and 3 day post-exercise biopsies compared to baseline of low responders. MLCK C49T single polymorphism was present in 26% of volunteers, whose CK responses were not higher than those with MLCK CC or CT genotype. In conclusion, perceived pain is more effectively assessed with potentially affected muscle under eccentric strain, even if static. High CK responders also have pronounced CRP responses to unaccustomed plyometric exercise intervention. Exertional rhabdomyolysis after unaccustomed eccentric exercise may be related to underlying inability to resolve intramuscular MPO.
PURPOSE: This study aimed to determine the effects of bilateral and unilateral eccentric exercises on muscle damage and muscular physiological indices in healthy men.
METHODS: Using a randomized ...crossover design, nine adult males without musculoskeletal disorders were divided into a bilateral eccentric exercise group (BEG, n=9) and a unilateral eccentric exercise group (UEG, n=9). Bilateral and unilateral eccentric exercises involved five sets of six repetitions of the rhythm metronome speed eccentric contraction 3 seconds at 110% one repetition maximum (1RM) using bilateral of BEG and the dominant and non-dominant of UEG separated by four weeks, respectively. Muscle damage (flexed and extended ROM, CIR, and VAS) and muscular physiological indices (muscle activity, muscle fatigue, and muscle tone) were measured before, immediately after (0 hour), 24, 48, 72, and 96 hours following bilateral and unilateral eccentric exercises.
RESULTS: The flexed ROM, CIR, VAS, muscle activity, and muscle tone were significantly increased after both bilateral and unilateral eccentric exercises (p<.05, respectively). Extended ROM and muscle activity significantly decreased after both bilateral and unilateral eccentric exercises (p<.05, respectively). However, there was no significant interaction between side (S) and time and side (T×S).
CONCLUSIONS: These results showed that there was no difference in muscle damage and physiological indices after measuring and setting the 1RM muscle strength separated by bilateral and unilateral eccentric exercises. KCI Citation Count: 0
Purpose The aim of this study was to investigate whether or not a single whole-body vibration treatment after eccentric exercise can reduce muscle soreness and enhance muscle recovery. Subjects and ...Methods Twenty untrained participants were randomly assigned to two groups: a vibration group (n=10) and control group (n=10). Participants performed eccentric quadriceps training of 4 sets of 5 repetitions at 120% 1RM, with 4 min rest between sets. After that, the vibration group received 3 sets of 1 min whole body vibration (12 Hz, 4 mm) with 30 s of passive recovery between sets. Serum creatine kinase, blood urea nitrogen, muscle soreness (visual analog scale) and muscle strength (peak isometric torque) were assessed. Results Creatine kinase was lower in the vibration group than in the control group at 24 h (200.2 ± 8.2 vs. 300.5 ± 26.1 U/L) and at 48 h (175.2 ± 12.5 vs. 285.2 ± 19.7 U/L) post-exercise. Muscle soreness decreased in vibration group compared to control group at 48 h post-exercise (34.1 ± 11.4 vs. 65.2 ± 13.2 mm). Conclusion Single whole-body vibration treatment after eccentric exercise reduced delayed onset muscle soreness but it did not affect muscle strength recovery.
This study examined the effects of low-intensity eccentric exercise training performed before high-intensity eccentric exercise on muscle damage markers, oxidative stress and antioxidant defense. ...Twenty-two rats were divided into 3 groups; control (CON; n = 6), high-intensity eccentric exercise (HE; n = 8) and low-intensity eccentric exercise training plus high-intensity eccentric exercise (LET + HE; n = 8). Rats in the HE group performed HE at once. Rats in the LET + HE group performed LET and then HE protocol was applied. Blood and vastus intermedius muscle samples were taken 24 hours after the last exercise session for analyses of muscle damage, oxidative stress, and antioxidant defense markers. Muscle damage markers were higher in the HE group than the CON (137%-488%) and the LET + HE groups (82%-110%) (P < 0.05). Oxidative stress marker was higher in the HE group than the CON (65%) and the LET + HE (50%) groups (P < 0.05). Antioxidant defense markers were higher in the LTE + HE group than the HE group (39%-51%) (P < 0.05). In conclusion, low-intensity eccentric exercise training performed before high-intensity eccentric exercise conferred a protective effect against muscle damage by reducing oxidative stress and increasing antioxidant defense.
The impact of eccentric exercise on mitochondrial function has only been poorly investigated and remains unclear. This study aimed to identify the changes in skeletal muscle mitochondrial ...respiration, specifically triggered by a single bout of eccentric treadmill exercise.
Male adult mice were randomly divided into eccentric (ECC, downhill running), concentric (CON, uphill running) and unexercised control groups (n = 5/group). Running groups performed 18 bouts of 5 min at 20 cm.s-1 on an inclined treadmill (+ or - 15 to 20°). Mice were sacrificed 48 hours post exercise for blood and quadriceps muscles collection. Deep proximal (red) and superficial distal (white) muscle portions were used for high-resolution respirometric measurements.
Plasma creatine kinase activity was significantly higher in ECC compared to CON group, reflecting exercise-induced muscle damage (p < 0.01). The ECC exercise induced a significant decrease in oxidative phosphorylation capacity in both quadriceps femoris parts (p = 0.032 in proximal portion, p = 0.010 in distal portion) in comparison with the CON group. This observation was only made for the NADH pathway using pyruvate+malate as substrates. When expressed as a flux control ratio, indicating a change related to mitochondrial quality rather than quantity, this change appeared more prominent in distal compared to proximal portion of quadriceps muscle. No significant difference between groups was found for the NADH pathway with glutamate or glutamate+malate as substrates, for the succinate pathway or for fatty acid oxidation.
Our data suggest that ECC exercise specifically affects pyruvate mitochondrial transport and/or oxidation 48 h post exercise and this alteration mainly concerns the distal white muscle portion. This study provides new perspectives to improve our understanding of the mitochondrial adaptation associated with ECC exercise.
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