Neuromuscular Adaptations to Work-matched Maximal Eccentric versus Concentric Training

Abstract

It is unclear whether the superiority of eccentric over concentric training on neuromuscular improvements is due to higher torque (mechanical loading) achievable during eccentric contractions or due to resulting greater total work.PurposeThis study aimed to examine neuromuscular adaptations after maximal eccentric versus concentric training matched for total work.MethodsTwelve males conducted single-joint isokinetic (180°·s−1) maximal eccentric contractions of the knee extensors in one leg (ECC-leg) and concentric in the other (CON-leg), 6 sets per session (3–5 sets in the initial 1–3 sessions), 2 sessions per week for 10 wk. The preceding leg performed 10 repetitions per set. The following leg conducted the equivalent volume of work. In addition to peak torque during training, agonist EMG and MRI-based anatomical cross-sectional area (ACSA) and transverse relaxation time (T2) at midthigh as reflective of neural drive, hypertrophy, and edema, respectively, were assessed weekly throughout the training period and pre- and posttraining. Whole muscle volume was also measured pre- and posttraining.ResultsTorque and EMG (in trained contraction conditions) significantly increased in both legs after week 1 (W1) and week 4 (W4), respectively, with a greater degree for ECC-leg (torque +76%, EMG +73%: posttraining) than CON-leg (+28%, +20%). ACSA significantly increased after W4 in ECC-leg only (+4%: posttraining), without T2 changes throughout. Muscle volume also increased in ECC-leg only (+4%). Multiple regression analysis revealed that changes (%Δ) in EMG solely explained 53%–80% and 30%–56% of the total variance in %Δtorque through training in ECC-leg and CON-leg, respectively, with small contributions (+13%–18%) of %ΔACSA for both legs.ConclusionEccentric training induces greater neuromuscular changes than concentric training even when matched for total work, whereas most of the strength gains during 10-wk training are attributable to the increased neural drive.

Single-joint eccentric knee extension training preferentially trains the rectus femoris within the quadriceps muscles

“…After training one leg, the equivalent volume of work per set was performed by the contralateral leg with the assigned contraction mode (ie, the number of repetitions was manipulated each set). This made it necessary for CON‐leg to perform more repetitions than ECC‐leg to match the total work (results detailed in our previous study) . The preceding leg was counterbalanced in the first training session among participants, and it was switched every session for each participant.…”

“…EMG was recorded using a wireless EMG system (Trigno; Delsys, Boston, USA). Following skin preparation, surface EMG electrodes were placed over the belly of RF, vastus lateralis (VL), and vastus medialis (VM) at 50% (RF, VL) and 80% (VM) of the thigh length (distance between the greater trochanter and lateral femoral condyle) and parallel to the presumed orientation of the muscle fibers . EMG signals were amplified (×300) and bandpass‐filtered (20‐ to 450‐Hz) at source and sampled at 2000 Hz via the same A/D converter and computer software as for the torque signal.…”

“…In another recent study of ours, we compared changes in QF muscle size following work‐matched single‐joint maximal ECC vs concentric (CON) knee extension training conducted for 10 weeks. After the intervention, only ECC training induced a significant increase in muscle size, suggesting that an ECC stimulus promotes muscle hypertrophy .…”

“…After the intervention, only ECC training induced a significant increase in muscle size, suggesting that an ECC stimulus promotes muscle hypertrophy . In that study, we reported muscle size data as muscle volume of the “whole” QF (ie, the sum of all QF muscles) because comparing hypertrophic responses of “individual” QF muscles was not the purpose of that study . In addition, we measured T 2 weekly throughout the training period and pre‐ and post‐training, but again only the representative values for the QF (ie, an average of all QF muscles) were reported.…”

“…We also hypothesized that CON training would not necessarily result in such preferential hypertrophy because of its insufficient overall hypertrophy (ie, no increase in whole QF muscle volume) after the intervention, which is likely due to low mechanical stress by choosing a fast velocity (180°/s) for the training velocity (discussed in more detail in our previous study) . Additionally, we calculated changes in strength and concomitant muscle activity during maximal ECC, CON, and isometric (ISO) contractions following the ECC and CON training to provide comprehensive information on training‐induced changes in strength and muscle activity, which were only partly reported in our previous study . It is worth noting that ECC strength is suggested to contribute to reducing the risk of strains .…”