Knee Extensor Fatigability During Different Resistance Exercise Protocols in Young and Old Adults
Date of Award
Master of Science (MS)
Clinical and Translational Rehabilitation Health Science
Hunter, Sandra K.
Aging is associated with decreased muscle strength, power, and contraction velocity, and increased fatigability of the lower limb muscles during dynamic contractions. The aims of this thesis were to compare young in and old men and women in: (1) fatigability of the knee extensors for two types of dynamic fatiguing protocols that are the basis of resistance training protocols, and (2) the central and peripheral mechanisms of fatigue during the two types of dynamic fatiguing protocols. Twenty young (19-24, 22.2 ± 1.3 years, men = 10) and twenty old adults (64-85, 73.8 ± 5.4, men = 10) performed: two different resistance training protocols, one high load high velocity protocol (HLP) and one low load low velocity protocol (LLP), each completing 4 sets of 8 repetitions. Before and after each protocol, the following were assessed: voluntary activation using muscle stimulation and the interpolated twitch technique as a measure of central fatigue, and contractile properties evoked with electrical stimulation as a measure of peripheral fatigue. The LLP of the knee extensor muscles induced greater reductions in isometric force than the HLP (P < 0.05) (21% vs. 12% reduction) across all four exercise sets, resulting in greater fatigability for the LLP. A more rapid recovery of MVIC force for the young adults compared to the old was observed (P < 0.05). The LLP also showed a greater reduction in the rate of force development than the HLP (P < 0.05). The reduction in MVIC force was associated with the reductions in twitch amplitude (r² = 0.368, P < 0.001) and voluntary activation (r2 = 0.209, P < 0.05) for the LLP but not the HLP (P > 0.05). The LLP protocol induced greater fatigability of the knee extensor muscles than the HLP, evidenced by greater reductions in MVIC. Muscular mechanisms were the primary contributor to the differences with a smaller contribution from neural mechanisms.