Comparison of two methods for measuring hamstring reaction time using the Kin-Com isokinetic dynamometer

Reaction Times and Electromechanical Delay in Reactions of Increasing and Decreasing Force

The purpose of this study was to compare reaction times and electromechanical delay between reactions to increase force from rest and reactions to decrease force from an active state in the quadriceps femoris of healthy young adults. Force, position, and electromyographic data were recorded from 35 subjects reacting to a forced knee-flexion perturbation. Electromechanical delay was assessed through cross-correlation of the filtered EMG and force data. Reaction time to increase force ( M = 159.9 msec., 95% CI = 149.9–169.9 msec.) was significantly longer than RT to decrease force ( M = 124.4 msec., 95% CI = 118.7–130.1 msec.). This difference was partially caused by a difference in electromechanical delay (RT to increase force electromechanical delay was 63 msec., 95% CI = 60–67 msec., greater than the RT to decrease force electromechanical delay of 49 msec., 95% CI = 46–52 msec.). This difference in reaction time could be important in identifying and interpreting physiologically meaningful changes in muscle force and in intermuscular coordination during movement.

The effects of proprioceptive or strength training on the neuromuscular function of the ACL reconstructed knee: a randomized clinical trial

OBJECTIVES

The purpose of this study was to determine the effects of a proprioceptive training program (PT) vs. a strength training (ST) program on neuromuscular function after anterior cruciate ligament (ACL) reconstruction. The second purpose was to establish the determinants of functional ability for the operated limb.

METHODS

Ten participants with unilateral ACL reconstructions were randomly assigned to one of the following 12-week training protocols: (1) isotonic ST, and (2) PT. The outcome measures were: (1) peak torque time of the hamstring muscles (PeakTT), (2) average concentric and eccentric torques of the quadriceps and hamstring muscles, (3) one-legged single hop for distance (SLHD), (4) one-legged time hop (TH), and (5) subjective scores.

RESULTS

: There was a significant group by time interaction effect for PeakTT (P = 0.017). The PT group demonstrated greater percent change in isokinetic torques than the ST group at the end of the 12 weeks (P < or = 0.05). Participants in both groups demonstrated similar significant gains in functional ability and subjective scores (P < or = 0.014). Quadriceps strength is a determinant of functional ability for the operated limb (R2 = 0.72).

CONCLUSIONS

: Both training protocols influenced PeakTT. The beneficial effects of ST on PeakTT appear to be load-dependent, while sufficient practice may be crucial in maintaining PeakTT improvements induced by PT. Proprioceptive training alone can induce isokinetic strength gains. Restoring and increasing quadriceps strength is essential to maximize functional ability of the operated knee joint.

Assessment of neuromuscular response characteristics at the knee following a functional perturbation

Previous research indicates that both the extent and timing of muscular activation at the knee can be influenced by muscle activity state, joint angle, weight-bearing status and trunk position. However, little research to date has evaluated protective neuromuscular response times and activation patterns to an imposed perturbation with the knee joint in a functional, weight-bearing stance. Hence, we designed a lower extremity perturbation device to produce a sudden, forward and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Surface electromyography (EMG) recorded long latency reflex times of the medial and lateral quadriceps, hamstring and gastrocnemius muscles in 64 intercollegiate lacrosse and soccer players in response to both internal and external rotation perturbation. We found the gastrocnemius fired significantly faster that the hamstring, which in turn fired significantly faster than the quadriceps. There was also a significant difference in activation times of the medial and lateral hamstring not found for the quadriceps or gastrocnemius muscles. Our findings confirmed that reactive neuromuscular responses following this functional perturbation differ markedly from those previously reported using seated, partial weight-bearing and/or uni-planar models under relaxed conditions.