An investigation of the relationship between impact force attenuation in landing and isokinetic strength of knee muscles in individuals with different training backgrounds

Skeletal muscle is a major active mechanism of impact force attenuation in human movement. During the landing phase impact attenuation is achieved through eccentric contraction of the muscles of the lower extremity. However, few studies have investigated the effects of knee strength, especially eccentric strength, on impact attenuation during landing. Therefore the relationship was assessed in fourteen healthy, male volunteers. Seven NCAA Division I College football players (TRAINED) and seven recreationally active university students with limited sport training or competitive sport background (REC) participated in two testing sessions. Isokinetic testing of the knee extensor and flexor muscles was performed concentrically at 60 and 180 degree·sec- 1, and eccentrically at 60 degree·sec-1. 3D kinematic and ground reaction force (GRF) data were collected during drop landings from heights of 40, 60cm and 100% of each individuals maximum jump height. The TRAINED had greater concentric strength, vertical jump height, but no significant differences existed in the eccentric strength (336 vs 340 N.m/kg) between the groups. The TRAINED had marginally greater peak GRFs (2.7 & 3.5 BW vs 2.0 & 2.7 BW for 40 and 60 cm, p=0.051) and significantly less time to the peak (0.048 & 0.043 s vs 0.060 & 0.053) compared to the REC in drop landing. The TRAINED used less but non-significant knee flexion range of motion (-60.7 & -54.1 degree vs -62.7 & -69.6 degree) during drop landing than the REC. There were high, positive and significant correlations between the peak eccentric knee extensor torque and time to the first and second peak GRF. Despite all their training the results did not find any significant differences in eccentric strength of the TRAINED subjects in comparison to their REC counterparts. The TRAINED subjects adopted a stiffer landing strategy to deal effectively with high impact loading during landing. Future research is warranted in investigating impact attenuation in landing of participants with significantly different eccentric strength.

KEY WORDS. Eccentric strength, dynamometer, drop landing, training