Low-intensity Eccentric Contractions Research Articles

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.

Damage protective effects conferred by low-intensity eccentric contractions on arm, leg and trunk muscles.

Low-intensity eccentric contractions with a load corresponding to 10% of maximal voluntary isometric contraction strength (10% EC) attenuate muscle damage in a subsequent bout of higher-intensity eccentric contractions performed within 2 weeks for the elbow flexors, knee flexors and knee extensors. However, it is not known whether this strategy could be applied to other muscles. This study investigated whether 10% EC would confer damage protective effect on high-intensity eccentric contractions (80% EC) for nine different muscle groups. Untrained young men were placed to an experimental or a control group (n = 12/group). Experimental group performed 50 eccentric contractions with a load corresponding to 10% EC at 2 days prior to 50 eccentric contractions with 80% EC for the elbow flexors and extensors, pectoralis, knee flexors and extensors, plantar flexors, latissimus, abdominis and erector spinae. Control group performed 80% EC without 10% EC. Changes in maximal voluntary isometric contraction strength (MVC) and muscle soreness, plasma creatine kinase (CK) activity and myoglobin concentration after 80% EC were compared between groups by a mixed-factor ANOVA. MVC recovered faster (e.g., 6-31% greater MVC at 5 days post-exercise), and peak muscle soreness was 36-54% lower for Experimental than Control group for the nine muscles (P < 0.05). Increases in plasma CK activity and myoglobin concentration were smaller for Experimental (e.g., peak CK: 2763 ± 3459IU/L) than Control group (120,360 ± 50,158IU/L). These results showed that 10% EC was effective for attenuating the magnitude of muscle damage after 80% EC for all muscles, although the magnitude of the protective effect differed among the muscles.

The effect of eccentric exercise with blood flow restriction on neuromuscular activation, microvascular oxygenation, and the repeated bout effect.

To examine the effect of low-intensity eccentric contractions with and without blood flow restriction (BFR) on microvascular oxygenation, neuromuscular activation, and the repeated bout effect (RBE). Participants were randomly assigned to either low-intensity (LI), low-intensity with BFR (LI-BFR), or a control (CON) group. Participants in LI and LI-BFR performed a preconditioning bout of low-intensity eccentric exercise prior to about of maximal eccentric exercise. Participants reported 24, 48, 72, and 96h later to assess muscle damage and function. Surface electromyography (sEMG) and near-infrared spectroscopy (NIRS) were used to measure neuromuscular activation and microvascular deoxygenation (deoxy-[Hb + Mb]) and [total hemoglobin] ([THC]) during the preconditioning bout, respectively. During set-2, LI-BFR resulted in greater activation of the VM-RMS (47.7 ± 11.5% MVIC) compared to LI (67.0 ± 20.0% MVIC), as well as during set-3 (p < 0.05). LI-BFR resulted in a greater change in deoxy-[Hb + Mb] compared to LI during set-2 (LI-BFR 13.1 ± 5.2µM, LI 6.7 ± 7.9µM), set-3 (LI-BFR 14.6 ± 6µM, LI 6.9 ± 7.4µM), and set-4 (p < 0.05). [THC] was higher during LI-BFR compared to LI (p < 0.05). All groups showed a decrease in MVIC torque immediately after maximal exercise (LI 74.2 ± 14.1%, LI-BFR 75 ± 5.1%, CON 53 ± 18.6%). At 24, 48, 72, and 96h post maximal eccentric exercise, LI and LI-BFR force deficit was not different from baseline. This study suggests that the neuromuscular and deoxygenation (i.e., metabolic stress) responses were considerably different between LI and LI-BFR groups; however, these differences did not lead to improvements in the RBE inferred by performing LI and LI-BFR.

Prevention of downhill walking-induced muscle damage by non-damaging downhill walking.

PurposeMountain trekking involves level, uphill, and downhill walking (DW). Prolonged DW induces damage to leg muscles, reducing force generating ability and muscle coordination. These increase risks for more serious injuries and accidents in mountain trekking, thus a strategy to minimize muscle damage is warranted. It has been shown that low-intensity eccentric contractions confer protective effect on muscle damage induced by high-intensity eccentric contractions. This study tested the hypothesis that 5-min non-damaging DW would attenuate muscle damage induced by 40-min DW, but 5-min level walking (LW) would not.MethodsUntrained young men were allocated (n = 12/group) to either a control or one of the two preconditioning groups (PRE-DW or PRE-LW). The PRE-DW and PRE-LW groups performed 5-min DW (-28%) and 5-min LW, respectively, at 5 km/h with a load of 10% body mass, 1 week before 40-min DW (-28%, 5 km/h, 10% load). The control group performed 40-min DW only. Maximal knee extension strength, plasma creatine kinase (CK) activity, and muscle soreness (0–100 mm visual analogue scale) were measured before and 24 h after 5-min DW and 5-min LW, and before and 24, 48, and 72 h after 40-min DW.ResultsNo significant changes in any variables were evident after 5-min DW and 5-min LW. After 40-min DW, the control and PRE-LW groups showed significant (P<0.05) changes in the variables without significant differences between groups (control vs. PRE-LW; peak strength reduction: -19.2 ± 6.9% vs. -18.7 ± 11.0%, peak CK: 635.5 ± 306.0 vs. 639.6 ± 405.4 U/L, peak soreness: 81.4 ± 14.8 vs. 72.0 ± 29.2 mm). These changes were significantly (P<0.05) attenuated (47–64%) for the PRE-DW group (-9.9 ± 9.6%, 339.3 ± 148.4 U/L, 27.8 ± 16.8 mm).ConclusionsThe results supported the hypothesis and suggest that performing small volume of downhill walking is crucial in preparation for trekking.

Low-intensity eccentric contractions of the knee extensors and flexors protect against muscle damage.

This study investigated the magnitude and duration of the protective effect of low-intensity eccentric contractions (LowEC) against damage induced by maximal eccentric contractions (MaxEC) of the knee flexors (KF) and extensors (KE). Young men were assigned to 8 experimental groups and 2 control groups (n = 13/group); the experimental groups performed LowEC of KF or KE 2 days (2d), 1 week (1wk), 2 weeks (2wk), or 3 weeks (3wk) before MaxEC, while the control groups performed MaxEC of KF or KE without LowEC. The 2d, 1wk, 2wk, and 3wk groups performed 30 LowEC of KF or 60 LowEC of KE with a load of 10% of maximal voluntary isometric contraction strength on a resistance-training machine, and all groups performed 30 MaxEC of KF or 60 MaxEC of KE on an isokinetic dynamometer. Several muscle damage markers were measured from before to 2 days after exercise (LowEC) or from before to 5 days after exercise (MaxEC). No significant changes in any variables were evident after LowEC. The changes in all variables after MaxEC were smaller (P < 0.05) for the 2d and 1wk groups (e.g., peak creatine kinase activity: 1002 ± 501 IU/L; peak muscle soreness: 13 ± 5 mm) than for the control group (peak creatine kinase activity: 3005 ± 983 IU/L; peak muscle soreness 28 ± 6 mm) for both KE and KF. There were no significant differences between the 2d and 1wk groups or among the 2wk, 3wk, and control groups. These results show that LowEC provided 30%-66% protection against damage induced by MaxEC of KF and KE, and the protective effect lasted 1 week.

Low-intensity Eccentric Contractions Attenuate Maximal Eccentric Contraction-induced Muscle Damage of the Knee Extensors

Low-intensity Eccentric Contractions Attenuate Maximal Eccentric Contraction-induced Muscle Damage of the Knee Extensors

Low-intensity eccentric contractions attenuate muscle damage induced by subsequent maximal eccentric exercise of the knee extensors in the elderly

This study investigated whether low-intensity eccentric contractions of the knee extensors would attenuate the magnitude of muscle damage induced by maximal eccentric exercise of the same muscle performed 7 days later using elderly individuals. Healthy older men (66.4 ± 4.6 years) were assigned to control or experimental (Exp) group (n = 13 per group). The control group performed six sets of ten maximal eccentric contractions (MaxECC) of the knee extensors of non-dominant leg. The Exp group performed six sets of ten low-intensity eccentric contractions of the knee extensors on a leg extension machine by lowering a weight of 10 % maximal voluntary isometric knee extension strength (10 %ECC) 7 days prior to MaxECC. Changes in maximal voluntary isokinetic concentric torque (MVC-CON), angle at peak torque, range of motion (ROM), upper thigh circumference, muscle soreness, plasma creatine kinase activity and myoglobin (Mb) concentration and B-mode ultrasound echo-intensity before and for 5 days after MaxECC were compared between groups by a mixed factor ANOVA. No significant changes in any variables were observed following 10 %ECC. Following MaxECC, all variables changed significantly, and changes in all variables except for angle at peak torque were significantly different between groups. MVC-CON and ROM decreased smaller and recovered faster (P < 0.05) for Exp than control group, and changes in other variables were smaller (P < 0.05) for Exp group compared with control group. These results suggest that preconditioning knee extensor muscles with low-intensity eccentric contractions was effective for attenuating muscle damage induced by subsequent MaxECC of the knee extensors for elderly individuals.

Muscle damage protection by low-intensity eccentric contractions remains for 2 weeks but not 3 weeks

This study investigated the hypothesis that the protective effect conferred by a low-intensity eccentric exercise against maximal eccentric exercise would not last more than a week. Untrained men (21.3 ± 1.6 years) were allocated into either a control or one of four repeated bout groups (n = 13 per group). The repeated bout groups performed 30 low-intensity eccentric contractions (ECC) of the elbow flexors with a dumbbell set at 10% of maximal isometric strength (10%-ECC) either 2 days, 7 days (1 week), 14 days (2 weeks) or 21 days (3 weeks) before 30 maximal eccentric contractions (Max-ECC). The control group performed Max-ECC only. Changes in maximal voluntary contraction strength, optimum angle, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration, and ultrasound echo-intensity following 10%-ECC were analysed by a one-way repeated measures ANOVA. Changes in the variables following Max-ECC were compared among the groups by a two-way repeated measures ANOVA. The 10%-ECC did not change any variables, showing no indication of muscle damage. The changes in all variables following Max-ECC were smaller (P < 0.05) for 2-day, 1- and 2-week groups than control group, without significant differences between 2-day and 1-week groups. The 2-week group showed greater (P < 0.05) changes in all variables compared with 2-day and 1-week groups. Changes in the variables were similar between 3-week and control groups, except for muscle soreness showing smaller (P < 0.05) changes for 3-week group. These results suggest that non-damaging eccentric exercise confers a protective effect against Max-Ecc, but the effect is attenuated between 1 and 2 weeks.

Differences in activation patterns between eccentric and concentric quadriceps contractions

Previous studies analysing electromyograms (EMGs) from indwelling electrodes have indicated that fast-twitch motor units are selectively recruited for low-intensity eccentric contractions. The aim of this study was to compare the frequency content of surface EMGs from quadriceps muscles during eccentric and concentric contractions at various contraction intensities. Electromyograms were recorded from the rectus femoris, vastus lateralis and vastus medialis muscles of 10 men during isokinetic (1.05 rad·s -1) eccentric and concentric knee extension contractions at 25%, 50%, 75% and 100% of maximal voluntary contraction (MVC) for each contraction mode. Additionally, isometric contractions (70°) were performed at each intensity. The mean frequency and root mean square (RMS) of the surface EMG were computed. Mean frequency was higher for eccentric than concentric contractions at 25% (P ≪ 0.01), 50% (P ≪ 0.01) and 75% (P ≪ 0.05) but not at 100% MVC. It increased with increasing contraction intensity for isometric (P ≪ 0.001) and concentric (P ≪ 0.01) contractions but not for eccentric contractions (P = 0.27). The EMG amplitude (RMS) increased with increasing contraction intensity similarly in each contraction mode (P ≪ 0.0001). Higher mean frequencies for eccentric than concentric contractions at submaximal contraction intensities is consistent with more fast-twitch motor units being active during eccentric contractions.