Strength and power changes of the human plantar flexors and knee extensors in response to resistance training in old age

Aim: The aim of the present study was to assess and compare the improvements of muscle strength and power induced by a 16-week resistive programme in a population of 16 older men aged 65-81 years. Methods: Training was performed three times per week at an intensity of 80% of one repetition maximum (1RM) and consisted of both calf raise and leg press exercises. Before-, during- and after-training, maximum isometric and isokinetic torques, maximum power, 1RM, muscle cross-sectional area (CSA) and electromyographic activity (EMG) of the plantar flexors (PF) and knee extensors (KE) were examined. Results: For the KE and PF, respectively, training resulted in a 29.9 +/- 4.4% (mean +/- SE) and 21.6 +/- 5.4% increase in 1RM (P < 0.001-0.01), a 19.4 +/- 4.3 and 12.4 +/- 4.7% (P < 0.001-0.05) increase in maximum isometric torque, and a 24.1 +/- 6.3 and 33.1 +/- 10.9% (P < 0.05) increase in maximum muscle power, calculated from torque-angular velocity curves. The large increase in torque and power was partly accounted by a significant increase in the CSA of the PF (5.0 +/- 0.7%) and KE (7.4 +/- 0.7%), while no significant changes in integrated EMG activity of vastus lateralis and soleus muscles, and in extrapolated maximum shortening velocity were found. After training, a significant increase in torque/CSA (10.3 +/- 4%, P < 0.05) was found for the KE but not for the PF. Conclusion: Hence, hypertrophy cannot alone justify the increase in torque, and other factors, such as an increase in individual fibre-specific tension (in the case of KE), a decrease in antagonist muscles' coactivation, an improved co-ordination and an increased neural drive of the other heads of quadriceps may have contributed to the increments in strength. The significant increase in muscle power seems particularly noteworthy with respect to daily activities involving the displacement of the body over time, namely, the generation of muscle power.