Contralateral effects of eccentric resistance training on immobilized arm

This study compared the effects of contralateral eccentric‐only (ECC) and concentric‐/eccentric‐coupled resistance training (CON‐ECC) of the elbow flexors on immobilized arm. Thirty healthy participants (18‐34 y) were randomly allocated to immobilization only (CTRL; n = 10), immobilization and ECC (n = 10), or immobilization and CON‐ECC group (n = 10). The non‐dominant arms of all participants were immobilized (8 h·day^?1) for 4 weeks, during which ECC and CON‐ECC were performed by the dominant (non‐immobilized) arm 3 times a week (3‐6 sets of 10 repetitions per session) with an 80%‐120% and 60%‐90% of one concentric repetition maximum (1‐RM) load, respectively, matching the total training volume. Arm circumference, 1‐RM and maximal voluntary isometric contraction (MVIC) strength, biceps brachii surface electromyogram amplitude (sEMG_RMS), rate of force development (RFD), and joint position sense (JPS) were measured for both arms before and after immobilization. CTRL showed decreases (P < .05) in MVIC (?21.7%), sEMG_RMS (?35.2%), RFD (?26.0%), 1‐RM (?14.4%), JPS (?87.4%), and arm circumference (?5.1%) of the immobilized arm. These deficits were attenuated or eliminated by ECC and CON‐ECC, with greater effect sizes for ECC than CON‐ECC in MVIC (0.29: +12.1%, vs ?0.18: ?0.1%) and sEMG_RMS (0.31:17.5% vs ?0.15: ?5.9%). For the trained arm, ECC showed greater effect size for MVIC than CON‐ECC (0.47 vs 0.29), and increased arm circumference (+2.9%), sEMG_RMS (+77.9%), and RDF (+31.8%) greater (P < .05) than CON‐ECC (+0.6%, +15.1%, and + 15.8%, respectively). The eccentric‐only resistance training of the contralateral arm was more effective to counteract the negative immobilization effects than the concentric‐eccentric training.     

Rate of force development as a measure of muscle damage

This study tested the hypothesis that rate of force development (RFD) would be a more sensitive indirect marker of muscle damage than maximum voluntary isometric contraction (MVC) peak torque. Ten men performed one concentric cycling and two eccentric cycling (ECC1, ECC2) bouts for 30 min at 60% of maximal concentric power output with 2 weeks between bouts. MVC peak torque, RFD, and vastus lateralis electromyogram amplitude and mean frequency were measured during a knee extensor MVC before, immediately after and 1–2 days after each bout. The magnitude of decrease in MVC peak torque after exercise was greater (P < 0.05) for ECC1 (11–25%) than concentric cycling (2–12%) and ECC2 (0–16%). Peak RFD and RFD from 0–30 ms, 0–50 ms, 0–100 ms, to 0–200 ms decreased (P < 0.05) immediately after all cycling bouts without significant differences between bouts, but RFD at 100–200 ms interval (RFD_100–200) decreased (P < 0.05) at all time points after ECC1 (24–32%) and immediately after ECC2 (23%), but did not change after CONC. The magnitude of decrease in RFD_100–200 was 7–19% greater than that of MVC peak torque after ECC1 (P < 0.05). It is concluded that RFD_100–200 is a more specific and sensitive indirect marker of eccentric exercise‐induced muscle damage than MVC peak torque.     

Whey protein hydrolysate augments tendon and muscle hypertrophy independent of resistance exercise contraction mode

In a comparative study, we investigated the effects of maximal eccentric or concentric resistance training combined with whey protein or placebo on muscle and tendon hypertrophy. 22 subjects were allocated into either a high‐leucine whey protein hydrolysate + carbohydrate group (WHD) or a carbohydrate group (PLA). Subjects completed 12 weeks maximal knee extensor training with one leg using eccentric contractions and the other using concentric contractions. Before and after training cross‐sectional area (CSA) of m. quadriceps and patellar tendon CSA was quantified with magnetic resonance imaging and a isometric strength test was used to assess maximal voluntary contraction (MVC) and rate of force development (RFD). Quadriceps CSA increased by 7.3 ± 1.0% (P < 0.001) in WHD and 3.4 ± 0.8% (P < 0.01) in PLA, with a greater increase in WHD compared to PLA (P < 0.01). Proximal patellar tendon CSA increased by 14.9 ± 3.1% (P < 0.001) and 8.1 ± 3.2% (P = 0.054) for WHD and PLA, respectively, with a greater increase in WHD compared to PLA (P < 0.05), with no effect of contraction mode. MVC and RFD increased by 15.6 ± 3.5% (P < 0.001) and 12–63% (P < 0.05), respectively, with no group or contraction mode effects. In conclusion, high‐leucine whey protein hydrolysate augments muscle and tendon hypertrophy following 12 weeks of resistance training – irrespective of contraction mode.     

Eccentric cycling is more efficient in reducing fat mass than concentric cycling in adolescents with obesity

The benefits of eccentric (ECC) training on fat mass (FM) remain underexplored. We hypothesized that in obese adolescents, ECC cycling training is more efficient for decreasing whole‐body FM percentage compared to concentric (CON) performed at the same oxygen consumption (VO₂). Twenty‐four adolescents aged 13.4 ± 1.3 years (BMI > 90th percentile) were randomized to ECC or CON. They performed three cyclo‐ergometer sessions per week (30 min per session) for 12 weeks: two habituation, 5 at 50% VO_2peak, and 5 at 70% VO_2peak. Anthropometric measurements, body composition, maximal incremental CON tests, strength tests, and blood samples were assessed pre‐ and post‐training. Whole‐body FM percentage decreased significantly after compared to pretraining in both groups, though to a larger extent in the ECC group (ECC: ?10% vs CON: ?4.2%, P < 0.05). Whole‐body lean mass (LM) percentage increased significantly in both groups after compared to pretraining, with a greater increase in the ECC group (ECC: 3.8% vs CON: 1.5%, P <0.05). The improvements in leg FM and LM percentages were greater in the ECC group (?6.5% and 3.0%, P = 0.01 and P < 0.01). Quadriceps isometric and isokinetic ECC strength increased significantly more in the ECC group (28.3% and 21.3%, P < 0.05). Both groups showed similar significant VO_2peak improvement (ECC: 15.4% vs CON: 10.3%). The decrease in homeostasis model assessment of insulin resistance index was significant in the ECC group (?19.9%). In conclusion, although both ECC and CON cycling trainings are efficient to decrease FM, ECC induces greater FM reduction, strength gains, and insulin resistance improvements and represents an optimal modality to recommend for obese adolescents.     

Effects of eccentric versus concentric contractions of the biceps brachii on intracortical inhibition and facilitation

Differences in the neural mechanisms underpinning eccentric (ECC) and concentric (CON) contractions exist; however, the acute effects of fatiguing muscle contractions on intracortical and corticospinal excitability are not well understood. Therefore, we compared maximal ECC and CON contractions of the right biceps brachii (BB) muscle for changes in corticospinal excitability, short‐ (SICI) and long‐interval intracortical inhibition (LICI) and intracortical facilitation (ICF) up to 1 hour post‐exercise. Fourteen right‐handed adults (11 M/3F; 26.8 ± 2.9 year) undertook a single session of 3 sets of 10 maximal ECC or CON contractions (180‐second rest between sets) on an isokinetic dynamometer (40°/s) separated by 1 week, in a randomized crossover study. Maximum voluntary isometric contraction torque (MVIC), maximal muscle compound waves (M_MAX), and motor‐evoked potentials elicited through transcranial magnetic stimulation (TMS) were recorded via surface electromyography from the right BB. MVIC decreased (P < 0.001) immediately after ECC and CON contractions similarly, but the decrease was sustained at 1 hour post‐ECC contractions only. M_MAX was reduced immediately (P = 0.014) and 1 hour post‐exercise (P = 0.019) only for ECC contractions. SICI and ICF increased immediately after ECC and CON contractions (P < 0.001), but LICI increased only after ECC contractions (P < 0.001), and these increases remained at 1 hour post‐ECC contractions only. These findings suggest that ECC contractions induced a longer‐lasting neuromodulatory effect on intracortical inhibition and facilitation, which could indicate a central compensatory response to peripheral fatigue.     

Progressive resistance training temporarily alters hamstring torque-angle relationship

To examine the effects of eccentric and concentric progressive resistance training on muscle torque-angle relationship, 30 young adults were randomly allocated into three groups of 10, control (CTL), eccentric training (ECC) and concentric training (CON). The ECC and CON groups performed seven sessions over 3 weeks of progressive resistance training of the right hamstrings muscle, using a standard barbell and a leg curl machine. Torque-angle relationship was measured before and 4, 11 and 18 days after the end of training. Voluntary isometric torque was recorded at seven test angles, with the subject prone (20-80 degrees; 0 degrees is full extension). In the CON group, the angle of peak isometric torque increased from 46.0 +/- 5.2 degrees pre-training to 53.0 +/- 14.9 degrees on day 4 following training (P<0.05). In the ECC group, peak torque was increased over baseline on days 4 and 11 post-training, particularly at extended knee angles (P<0.05). The angle at which peak torque occurred was decreased on day 4 (50.0 +/- 8.2 degrees pre-training, 29.0 +/- 7.4 degrees on day 4) and on day 11 (both P<0.01), but was similar to baseline 18 days after training. ECC therefore induced a temporary change in torque-angle relationship.     

Muscular adaptations after two different volumes of blood flow‐restricted training

This study aimed to gain an insight into the adaptations of muscle strength and skeletal muscle thickness after two different volumes of blood flow restriction training (BFRT), and compare them with high‐intensity training. The sample was divided into four groups: low‐volume, low‐intensity BFRT (BFRT LV); high‐volume, low‐intensity BFRT (BFRT HV); traditional high‐intensity resistance training (HIT); and a control group, which maintained their routine activities (CON). Leg extension one repetition maximum (1RM), isokinetic peak knee extension, and flexion torques at 60°/s and 180°/s as well as muscle thickness of the rectus femoris (RF) and vastus lateralis (VL) were assessed at baseline and after 5 weeks of training BFRT LV (7.03%, P < 0.05), BFRT HV (6.24%, P < 0.05) and HIT (18.86%, P < 0.001) groups increased 1RM performance, while no changes were observed in the CON group. Muscle thickness of the RF and VL was increased irrespective of the training group (7.5%, P < 0.001; and 9.9%, P < 0.001, respectively). We conclude that doubling the exercise volume with BFRT causes no further benefit with muscular size or strength. Although similar increases in muscle thickness were observed between training groups, HIT increased 1RM performance to a greater extent compared to either volume of BFRT.     

The effects of flexibility training on exercise‐induced muscle damage in young men with limited hamstrings flexibility

Adaptations to 6 weeks of supervised hamstring stretching training and its potential impact on symptoms of eccentric exercise‐induced muscle damage (EIMD) were studied in 10 young, untrained men with limited hamstrings flexibility. Participants performed unilateral flexibility training (experimental leg; EL) on an isokinetic dynamometer, while the contralateral limb acted as control (CL). Hip range of motion (ROM), passive, isometric, and concentric torques, active optimum angle, and biceps femoris and semitendinosus muscle thickness and ultrasound echo intensity were assessed both before and after the training. Additionally, muscle soreness was assessed before and after an acute eccentric exercise bout in both legs (EL and CL) at post‐training only. Hip ROM increased (P  < .001) only in EL after the training (EL = 10.6° vs CL = 1.6°), but no changes (P  > .05) in other criterion measurements were observed. After a bout of eccentric exercise at the end of the program, isometric and dynamic peak torques and muscle soreness ratings were significantly altered at all time points equally in EL and CL. Also, active optimum angle was reduced immediately, 48 and 72 hours post‐exercise, and hip ROM was reduced at 48 and 72 hours equally in EL and CL. Finally, biceps femoris muscle thickness was significantly increased at all time points, and semitendinosus thickness and echo intensity significantly increased at 72 hours, with no significant differences between legs. The stretching training protocol significantly increased hip ROM; however, it did not induce a protective effect on EIMD in men with tight hamstrings.     

Neuromuscular response differences to power vs strength back squat exercise in elite athletes

The study's aim was to establish the neuromuscular responses in elite athletes during and following maximal ‘explosive’ regular back squat exercise at heavy, moderate, and light loads. Ten elite track and field athletes completed 10 sets of five maximal squat repetitions on three separate days. Knee extension maximal isometric voluntary contraction (MIVC), rate of force development (RFD) and evoked peak twitch force (Pt) assessments were made pre‐ and post‐session. Surface electromyography [root mean square (RMS)] and mechanical measurements were recorded during repetitions. The heavy session resulted in the greatest repetition impulse in comparison to moderate and light sessions (P < 0.001), while the latter showed highest repetition power (P < 0.001). MIVC, RFD, and Pt were significantly reduced post‐session (P < 0.01), with greatest reduction observed after the heavy, followed by the moderate and light sessions accordingly. Power significantly reduced during the heavy session only (P < 0.001), and greater increases in RMS occurred during heavy session (P < 0.001), followed by moderate, with no change during light session. In conclusion, this study has shown in elite athletes that the moderate load is optimal for providing a neuromuscular stimulus but with limited fatigue. This type of intervention could be potentially used in the development of both strength and power in elite athletic populations.     

Effects of eccentric training at long-muscle length on architectural and functional characteristics of the hamstrings

Hamstring strain injuries during sprinting or stretching frequently occur at long-muscle length. Yet, previous research has mainly focused on studying the effectiveness of eccentric hamstring strengthening at shorter muscle length on hamstring performance, morphology, and hamstring strain injury risk factors. Here, we evaluated the effects of 6-week eccentric hamstring training at long-muscle length on functional and architectural characteristics of the hamstrings. Healthy and injury-free participants (n = 40; age 23.7 ± 2.5 years) were randomly assigned to control or intervention group. Training intervention consisted of 12 sessions with two eccentric hamstring exercises in a lengthened position. Outcome measures included isokinetic and isometric knee flexion peak torque, Nordic hamstring exercise peak torque, voluntary activation level, and countermovement jump performance. Ultrasonography was used to determine muscle thickness, pennation angle, and fascicle length of biceps femoris long head (BFlh). A significant time × group interaction effect was observed for all measured parameters except countermovement jump performance and muscle thickness. The training intervention resulted in increased concentric and eccentric knee flexion peak torque at 60°/s (d = 0.55-0.62, P = .02 and .03) and concentric peak torque at 180°/s (d = 0.99, P = .001), increased isometric knee flexion peak torque (d = 0.73, P = .008) and Nordic hamstring exercise peak torque (d = 1.19, P < .001), increased voluntary activation level (d = 1.29, P < .001), decreased pennation angle (d = 1.31, P < .001), and increased fascicle length (d = 1.12, P < .001) of BFlh. These results provide evidence that short-term eccentric hamstring strengthening at long-muscle length can have significant favorable effects on various architectural and functional characteristics of the hamstrings.     

Effects of velocity loss during resistance training on athletic performance,strength gains and muscle adaptations

We compared the effects of two resistance training (RT) programs only differing in the repetition velocity loss allowed in each set: 20% (VL20) vs 40% (VL40) on muscle structural and functional adaptations. Twenty‐two young males were randomly assigned to a VL20 (n = 12) or VL40 (n = 10) group. Subjects followed an 8‐week velocity‐based RT program using the squat exercise while monitoring repetition velocity. Pre‐ and post‐training assessments included: magnetic resonance imaging, vastus lateralis biopsies for muscle cross‐sectional area (CSA) and fiber type analyses, one‐repetition maximum strength and full load‐velocity squat profile, countermovement jump (CMJ), and 20‐m sprint running. VL20 resulted in similar squat strength gains than VL40 and greater improvements in CMJ (9.5% vs 3.5%, P < 0.05), despite VL20 performing 40% fewer repetitions. Although both groups increased mean fiber CSA and whole quadriceps muscle volume, VL40 training elicited a greater hypertrophy of vastus lateralis and intermedius than VL20. Training resulted in a reduction of myosin heavy chain IIX percentage in VL40, whereas it was preserved in VL20. In conclusion, the progressive accumulation of muscle fatigue as indicated by a more pronounced repetition velocity loss appears as an important variable in the configuration of the resistance exercise stimulus as it influences functional and structural neuromuscular adaptations.     

Acute effects of static and dynamic stretching on leg flexor and extensor isokinetic strength in elite women athletes

The aim of this study was to explore the effects of static and dynamic stretching of the leg flexors and extensors on concentric and eccentric peak torque (PT) and electromyography (EMG) amplitude of the leg extensors and flexors in women athletes. Ten elite women athletes completed the following intervention protocol in a randomized order on separate days: (a) non‐stretching (control), (b) static stretching, and (c) dynamic stretching. Stretched muscles were the quadriceps and hamstring muscles. Before and after the stretching or control intervention, concentric and eccentric isokinetic PT and EMG activity of the leg extensors and flexors were measured at 60 and 180°/s. Concentric and eccentric quadriceps and hamstring muscle strength at both test speeds displayed a significant decrease following static stretching (P<0.01–0.001). In contrast, a significant increase was observed after dynamic stretching for these strength parameters (P<0.05–0.001). Parallel to this, normalized EMG amplitude parameters exhibited significant decreases following static (P<0.05–0.001) and significant increases following dynamic stretching (P<0.05–0.001) during quadriceps and hamstring muscle actions at both concentric and eccentric testing modes. Our findings suggest that dynamic stretching, as opposed to static or no stretching, may be an effective technique for enhancing muscle performance during the pre‐competition warm‐up routine in elite women athletes.     

Concentric versus eccentric cycling at equal power output or effort perception: Neuromuscular alterations and muscle pain

This study aimed to compare neuromuscular alterations and perceptions of effort and muscle pain induced by concentric and eccentric cycling performed at the same power output or effort perception. Fifteen participants completed three 30-min sessions: one in concentric at 60% peak power output (CON) and two in eccentric, at the same power output (ECC_POWER) or same perceived effort (ECC_EFFORT). Muscle pain, perception of effort, oxygen uptake as well as rectus femoris and vastus lateralis electromyographic activities were collected when pedaling. The knee extensors maximal voluntary contraction (MVC) torque, the torque evoked by double stimulations at 100 Hz and 10 Hz (Dt100; Dt10), and the voluntary activation level (VAL) were evaluated before and after exercise. Power output was higher in ECC_EFFORT than CON (89.1 ± 23.3% peak power). Muscle pain and effort perception were greater in CON than ECC_POWER (p < 0.03) while muscle pain was similar in CON and ECC_EFFORT (p > 0.43). MVC torque, Dt100, and VAL dropped in all conditions (p < 0.04). MVC torque (p < 0.001) and the Dt10/ Dt100 ratio declined further in ECC_EFFORT (p < 0.001). Eccentric cycling perceived as difficult as concentric cycling caused similar muscle pain but more MVC torque decrease. A given power output induced lower perceptions of pain and effort in eccentric than in concentric yet similar MVC torque decline. While neural impairments were similar in all conditions, eccentric cycling seemed to alter excitation-contraction coupling. Clinicians should thus be cautious when setting eccentric cycling intensity based on effort perception.     

Eccentric exercise in coronary patients: central hemodynamic and metabolic responses

PURPOSE: With lengthening (eccentric) muscle contractions, the magnitude of locomotor-muscle mass and strength increase has been demonstrated to be greater compared with shortening (concentric) muscle contractions. In healthy subjects, energy demand and heart rate responses with eccentric exercise are small relative to the amount of muscle force produced. Thus, eccentric exercise may be an attractive alternative to resistance exercise for patients with limited cardiovascular exercise tolerance. METHODS: We tested the cardiovascular tolerance of eccentric exercise in 13 coronary patients (ages 40-66) with preserved and/or mild reduced left ventricular function. Patients were randomly assigned to either an eccentric (ECC; N = 7) or a concentric (CON; N = 6) training group and trained for 8 wk. Training workload was increased progressively (from week 1 to 5) to an intensity equivalent to 60% [OV0312]O(2peak). RESULTS: On average, maximum power output achieved with ECC was fourfold compared with CON (357 +/- 96 W vs 97 +/- 21 W; P < 0.005), whereas measures of oxygen uptake and blood lactate were significantly lower (P < 0.05 each), and ratings of perceived exertion were similar for ECC and CON. During a 20-min session of ECC and CON, central hemodynamics was measured by means of right heart catheterization. During ECC, responses of mean arterial blood pressure, systemic vascular resistance, pulmonary capillary pressure, cardiac index, and stroke work of the left ventricle on average were in the normal range of values and similar to those observed during CON. Compared with baseline, after 8 wk of training, echocardiographic left ventricular function was unchanged. CONCLUSION: The results indicate uncoupling of skeletal muscle load and cardiovascular stress during ECC. For low-risk patients with coronary heart disease without angina, inducible ischemia, or left ventricular dysfunction, ECC can be recommended as a safe new approach to perform high-load muscular exercise training with minimal cardiovascular stress.     

Beetroot juice supplementation increases concentric and eccentric muscle power output. Original investigation

ObjectivesBeetroot juice (BJ) supplementation has been reported to enhance skeletal muscle contractile function; however, it is currently unclear whether BJ supplementation elicits comparable improvements in power output during different types of skeletal muscle contractions. The purpose of the current study was to assess the effect of BJ supplementation on power output during concentric (CON) and eccentric (ECC) muscle contractions during a half-squat.DesignIn a randomized, double-blind placebo-controlled crossover design, eighteen adult males (age: 22.8 ± 4.9 y) completed two experimental testing sessions 2.5 h following the acute ingestion of 140 mL nitrate-rich BJ concentrate or a placebo.MethodsEach experimental session comprised four sets of eight all-out half-squat repetitions with each set completed with a different moment intertia (0.025, 0.050, 0.075 and 0.100 kg·m^?2).ResultsCompared to placebo, BJ supplementation increased mean power output (MP) during the CON (ES: 0.61–1.01) and ECC (ES: 0.54–0.89; all p < 0.05) movement phases to a similar extent. Moreover, comparable increases in peak power output (PP) during the CON (ES: 0.86–1.24) and ECC (ES: 0.6–1.08; all p < 0.05) movement phases were observed following BJ supplementation.ConclusionAcute BJ supplementation increased mean and peak lower limb power output in the concentric and eccentric movement phases of a half-squat. These findings improve understanding of the effects of BJ supplementation on skeletal muscle contractile function and might have implications for enhancing sports performance in events where muscle power output is a key performance determinant.     

Effects of concurrent exercise training on muscle dysfunction and systemic oxidative stress in older people with COPD

Oxidative stress is associated with disease severity and limb muscle dysfunction in COPD. Our main goal was to assess the effects of exercise training on systemic oxidative stress and limb muscle dysfunction in older people with COPD. Twenty‐nine outpatients with COPD (66‐90 years) were randomly assigned to a 12‐week exercise training (ET; high‐intensity interval training (HIIT) plus power training) or a control (CT; usual care) group. We evaluated mid‐thigh muscle cross‐sectional area (CSA; computed tomography); vastus lateralis (VL) muscle thickness, pennation angle, and fascicle length (ultrasonography); peak VO₂ uptake (VO_2peak) and work rate (W_peak) (incremental cardiopulmonary exercise test); rate of force development (RFD); maximal muscle power (P_max; force‐velocity testing); systemic oxidative stress (plasma protein carbonylation); and physical performance and quality of life. ET subjects experienced changes in mid‐thigh muscle CSA (+4%), VL muscle thickness (+11%) and pennation angle (+19%), VO_2peak (+14%), W_peak (+37%), RFD (+32% to 65%), P_max (+38% to 51%), sit‐to‐stand time (?24%), and self‐reported health status (+20%) (all P < 0.05). No changes were noted in the CT group (P > 0.05). Protein carbonylation decreased among ET subjects (?27%; P < 0.05), but not in the CT group (P > 0.05). Changes in protein carbonylation were associated with changes in muscle size and pennation angle (r = ?0.44 to ?0.57), exercise capacity (r = ?0.46), muscle strength (r = ?0.45), and sit‐to‐stand performance (r = 0.60) (all P < 0.05). The combination of HIIT and power training improved systemic oxidative stress and limb muscle dysfunction in older people with COPD. Changes in oxidative stress were associated with exercise‐induced structural and functional adaptations.     

Evidence of neuromuscular fatigue after prolonged cycling exercise

PURPOSE: The purpose of this study was to analyze the effects of prolonged cycling exercise on metabolic, neuromuscular, and biomechanical parameters. METHODS: Eight well-trained male cyclists or triathletes performed a 2-h cycling exercise at a power output corresponding to 65% of their maximal aerobic power. Maximal concentric (CON; 60, 120, 240 degrees x s(-1)), isometric (ISO; 0 degrees s(-1)), and eccentric (ECC; -120, -60 degrees x s(-1)) contractions, electromyographic (EMG) activity of vastus lateralis (VL) and vastus medialis (VM) muscles were recorded before and after the exercise. Neural (M-wave) and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed using electrical stimulation techniques. RESULTS: Oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR) significantly increased (P < 0.01) during the 2-h by, respectively, 9.6%, 17.7%, and 12.7%, whereas pedaling rate significantly decreased (P < 0.01) by 21% (from 87 to 69 rpm). Reductions in muscular peak torque were quite similar during CON, ISO, and ECC contractions, ranging from 11 to 15%. M-wave duration significantly increased (P < 0.05) postexercise in both VL and VM, whereas maximal amplitude and total area decreased (VM: P < 0.05, VL: NS). Significant decreases in maximal twitch tension (P < 0.01), total area of mechanical response (P < 0.01), and maximal rate of twitch tension development (P < 0.05) were found postexercise. CONCLUSIONS: A reduction in leg muscular capacity after prolonged cycling exercise resulted from both reduced neural input to the muscles and a failure of peripheral contractile mechanisms. Several hypothesis are proposed to explain a decrease in pedaling rate during the 2-h cycling with a constancy of power output and an increase in energy cost.     

Effect of concentric and eccentric hamstring training on sprint recovery,strength and muscle architecture in inexperienced athletes

ObjectivesTo investigate whether five-weeks of concentric (CON) or eccentric (ECC) hamstring strength training have different effects on recovery from sprint running, eccentric strength and architecture of the biceps femoris long head (BF_LH).DesignCohort study.MethodsThirty males (age, 22.8 ± 4.1 y; height, 180.1 ± 6.4 cm; weight, 85.2 ± 14.6 kg) were allocated into either a CON or ECC group, both performing nine sessions of resistance training. Prior to and immediately after the five-week intervention, each participant’s BF_LH fascicle length (FL), pennation angle (PA), muscle thickness (MT), peak isometric KF torque and Nordic eccentric strength were assessed. Post-intervention, participants performed two timed sprint sessions (10 × 80 m) 48 h apart. Blood samples and passive KF torques were collected before, immediately after, 24 h and 48 h after the first sprint session.ResultsAfter five-weeks of strength-training, fascicles lengthened in the ECC (p < 0.001; d = 2.0) and shortened in the CON group (p < 0.001; d = 0.92), while PA decreased for the ECC (p = 0.001; d = 0.52) and increased in the CON group (p < 0.001; d = 1.69). Nordic eccentric strength improved in both ECC (p < 0.001; d = 1.49) and CON (p < 0.001; d = 0.95) groups. No between-group differences were observed in peak isometric strength (p = 0.480), passive KF torques (p = 0.807), sprint performance decrements between sprint sessions (p = 0.317) and creatine kinase (p = 0.818).ConclusionsDespite inducing significant differences in BF_LH muscle architecture, there were no significant between group differences in sprint performance decrements across two sprint sessions.     

Acute adaptation to low volume eccentric exercise.

PURPOSE: Many symptoms of eccentric muscle damage can be substantially reduced if a similar eccentric bout is repeated within several weeks of the initial bout. The purpose of this study was to determine whether a nondamaging, low repetition, low volume eccentric exercise bout could also provide a protective/adaptive effect. METHODS: Subjects were assigned to a control (CON), eccentric exercise (ECC), or low volume familiarized eccentric exercise group (LV+ECC). Before the study, the LV+ECC group performed six maximal eccentric contractions during two familiarization sessions. The main eccentric bout targeted the elbow flexor muscle group and consisted of 36 maximal eccentric contractions. Muscle soreness, upper arm girth, elbow angle, creatine kinase activity, isometric torque, and concentric and eccentric torque at 0.52 and 3.14 rad.s-1 were assessed 0, 1, 2, 3, 4, 7, and 10 d postexercise. RESULTS: No evidence of muscle damage was observed as a result of the low volume eccentric bouts. Nevertheless, with the exception of muscle soreness and concentric torque, all variables recovered more rapidly in the LV+ECC group (P < 0.05). CONCLUSION: Adaptation to eccentric exercise can occur in the absence of significant muscle damage. Exposure to a small number of nondamaging eccentric contractions can significantly improve recovery after a subsequent damaging eccentric bout. Furthermore, this adaptation appears to be mode-specific and not applicable to concentric contractions.