Neuromuscular Changes and Damage after Isoload versus Isokinetic Eccentric Exercise

PURPOSE

This study compared the effects of isoload (IL) and isokinetic (IK) knee extensor eccentric exercises on changes in muscle damage and neuromuscular parameters to test the hypothesis that the changes would be different after IL and IK exercises.

METHODS

Twenty-two young men were paired based on their strength and placed in the IL (N = 11) or the IK (N = 11) group. The IL group performed 15 sets of 10 eccentric contractions with a 150% of predetermined one-repetition maximum load. The IK group performed 15 sets of several maximal eccentric contractions matched set by set for the total amount of work and mean angular velocity with the IL group. Muscle damage markers (voluntary isometric peak torque, muscle soreness, and creatine kinase activity) and neuromuscular variables (e.g., voluntary activation, H-reflex, M-wave, and evoked torque) were measured before, immediately after, and 24, 48, 72, and 96 h postexercise.

RESULTS

Voluntary isometric peak torque decreased to the same extent (P = 0.94) in both groups immediately after (IL = -40.6% ± 13.8% vs IK = -42.4% ± 10.2%) to 96 h after the exercise (IL = -21.8% ± 28.5% vs IK = -26.7% ± 23.5%). Neither peak muscle soreness (IL = 48.1 ± 28.2 mm vs IK = 54.7 ± 28.9 mm, P = 0.57) nor creatine kinase activity (IL = 12,811 ± 22,654 U·L vs IK = 15,304 ± 24,739 U·L, P = 0.59) significantly differed between groups. H-reflex (IL = -23% vs IK = -35%) and M-wave (IL = -10% vs IK = -17%) significantly decreased immediately postexercise similarly between groups.

CONCLUSION

The changes in muscle damage and neuromuscular function after the exercise are similar between IL and IK, suggesting that resistance modality has little effects on acute muscle responses.

Comparison of two methodological approaches for the mechanical analysis of single-joint isoinertial movement using a customised isokinetic dynamometer. Sports Biomech 2017;17:287-302. [PMID: 28298168 DOI: 10.1080/14763141.2016.1269187]

Compared to isokinetic and isometric tests, isoinertial movements have been poorly used to assess single-joint performance. Two calculation procedures were developed to estimate mechanical performance during single-joint isoinertial movements performed on a customised isokinetic dynamometer. The results were also compared to appreciate the effects of measurement systems and calculation procedures. Five participants performed maximal knee extensions at four levels of resistance (30, 50, 70 and 90% of the one-repetition maximum, 1-RM). Joint angular velocity and torque were assessed from customised isokinetic dynamometer measures (method A) and from weight stack kinematic (method B). Bland-Altman plots and mean percent differences (M_diff) were used to assess the level of agreement for mean and peak angular velocity and torque. A Passing-Bablok regression was performed to compare the angular velocity-angle and torque-angle relationships computed from the two analysis methods. The results showed a high level of agreement for all mechanical parameters (M_diff < 6% for all parameters). No statistically significant differences were observed between methods A and B in terms of angular velocity-angle and torque-angle relationships except at 30% of 1-RM for the torque-angle relationship. Both methodologies provide comparable values of angular velocity and torque, offering alternative approaches to assess neuromuscular function from single-joint isoinertial movements.

Time-course of performance changes and underlying mechanisms during and after repetitive moderately weight-loaded knee extensions

The purpose of this study was to investigate the mechanisms of fatigue development induced by isoload (IL) fatiguing knee extensions. Nine physically active males (age=23±2years, height=179±7cm, mass=76±7kg) performed repetitive ballistic knee extensions at 30% of the isometric maximal voluntary peak torque. Fatigue development was assessed throughout the fatiguing exercise by quantifying changes in peak torque, agonist and antagonist electromyographic activity (EMG) and torque- and EMG-angle relationships. Before and after the fatiguing exercise, isometric maximal voluntary contractions were performed to measure peak torque (MVIC torque), voluntary activation (VA) and resting twitch torque. IL peak torque decreased from the middle of the fatiguing exercise while the agonist and antagonist EMG amplitude increased consistently during the entire exercise (P<.005). The pattern of the torque-angle relationship changed with fatigue (P<.005) reflecting a change in torque production strategy even if the EMG-angle relationships were not modified. Post-exercise testing revealed a decrease in MVIC torque (-31%; P<.005). VA was unchanged (P=.60) while the resting twitch torque was impaired to a great extent (-46%; P<.005) suggesting that local muscular mechanisms but not neural drive were altered during single-joint IL fatiguing task.