Objective: The purpose of this study was to evaluate the muscle activation patterns of lower limb muscles during 90-second trials at randomly assigned workloads (0 and 100 W) with a constant cadence (60 rpm) in young and older healthy adults.
Methods: Twelve healthy, male, novice cyclists classified by age into two groups of young and older. Electromyographic (EMG) data were recorded from rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius medialis (GT). Joints kinematics was also recorded simultaneously. A performance index (PI) was developed to evaluate the characteristics of muscle recruitment between workloads.
Results: EMG duration and peak magnitude increased significantly with increased workload in RF and BF in both groups. PI Values indicated that BF and RF had similar increases with increased workload for both groups, while younger groups had higher activation of TA (52% v/s 28%) and older group had higher activation of GT (17% v/s 1%). Both groups exhibited significant increases (p<0.05) in the co-activation of upper leg agonist and antagonist muscles as workload increased. Duration of co-activation between the upper and lower leg muscles of the young group significantly increased (p<0.05) with workload. The ROM of the knee splay angle in the older group showed a significant difference (p<0.05) compared to the young.
Conclusion: The alteration in limb muscle activation and coordination is not parallel between young and older adults. Older adults appear to use a different strategy in recruiting more muscle fibre to generate the same work. These findings are an indication that the threshold for muscle adaptation may differ between young and old adults. It is recommended that rehabilitation professionals consider these differences and recognize that the stimulus required to promote positive change in older skeletal muscles might be different from what may require for young adults.