Herzog, WalterPower, Geoffrey AlonzoDalton, BrianFlaaten, Nordan2016-06-212016-06-212016-06JAAA-D-15-00294R2http://hdl.handle.net/1880/51395With adult aging, eccentric strength is maintained better than isometric strength leading to a higher ratio of eccentric:isometric force production (ECC:ISO) in older than younger adults. The purpose was to investigate the ECC:ISO during electrical activation of the adductor pollicis during lengthening (20-320°∙s-1) contractions in 24 young (n=12, ~24 years) and old (n=12, ~72 years) males across muscle temperatures (Cold; ~19oC, Normal; ~30oC, Warm; ~35oC). For isometric force, the old were 20-30% weaker in the normal and cold conditions (P<0.05) with no difference for the warm condition compared to young (P>0.05). Half-relaxation time (HRT) did not differ across age for the normal and warm temperatures (P>0.05), but slowed significantly for old in the cold condition compared with young (~15%; P<0.05), as well, there was a 20 and 40% increase in muscle stiffness for the young and old, respectively. ECC:ISO was 50-60% greater for the cold condition than the normal and warm conditions. There was no age-difference in ECC:ISO across age for the normal and warm conditions (P>0.05), but for the cold, the old exhibited a 20-35% higher ECC:ISO than young for velocities above 60°∙s-1 (P<0.05). A contributing factor to the elevated ECC:ISO is an increased proportion of weakly- compared to strongly-bound cross-bridges. These findings highlight the relationship (r=0.70) between intrinsic muscle contractile speed (HRT) and eccentric strength in old age.enmusclelengtheningresidual force enhancementstiffnessweaknesssacropeniajournal article10.11575/PRISM/29053