The Relationship between Mechanical Stiffness, Dynamic Strength and Static Strength following Eccentric or Concentric Activity

Abstract

Workplace exertions can involve static, muscle lengthening (eccentric), or muscle shortening (concentric) exertions. The purpose of this study was to examine the relationship between mechanical stiffness, dynamic strength and static (isometric) strength following sub maximal eccentric or concentric exercise. Participants were randomly assigned to perform eccentric or concentric forearm supinations at 50% of isometric supination strength for 30 minutes. Mechanical stiffness, isometric and dynamic strength were measured prior, one hour after and 24 hours after exercise. Average mechanical stiffness decreased 31% (p < 0.05) after 24 hours for the eccentric group and decreased 16% (p > 0.05) for the concentric group. Average static strength in both groups recovered to within 2% of pre exercise levels for both groups after 24 hours. Average dynamic strength decreased 18% (p < 0.05) 24 hours after exercise for the eccentric group and increased 7% (p > 0.05) for the concentric group. Significant correlation (r = 0.664 to 0.832, p < 0.05) was observed between changes in mechanical stiffness and dynamic strength. Reductions in dynamic strength and mechanical stiffness persisted 24 hours after unaccustomed eccentric exertions but similar changes were not observed for static strength.