Attenuation of force deficit after lengthening contractions in soleus muscle from trained rats

The purposes of this study mere 1) to determine the extent to which endurance training reduces the functional deficit induced by lengthening contractions in the soleus (Sol) muscle and 2) to determine whether young and old rats training at a comparable relative exercise intensity would demonstrate a similar protective effect fi om lengthening-contraction-induced injury. Young (3-mo-old) and old (23-mo-old) male Fischer 844 rats were randomly assigned to either a control or exercise training group [young control (YC), old control (OC), young trained CYT), old trained (OT)]. Exercise training consisted of 10 wk of treadmill running (15% grade, 45 min/day, and 5 days/wk) such that by the end of training the young and old rats were exercising at 27 and 15 m/min, respectively. After training, contractile properties of the Sol muscle were measured in vitro at 26 degrees C. The percent decrease in maximal. isometric specific force (P-o) was determined after a series of 20 lengthening contractions (20% strain from optimal muscle length, 1 contraction every 5 s). After the lengthening-contraction protocol, Sol muscle P-o was decreased by similar to 26% (19.6 vs. 14.6 N/cm(2)) and 288 (14.8 vs. 9.6 N/cm(2)) in the YC and OC rats, respectively After exercise training, the reduction in P-o was significantly (P < 0.05) attenuated to a similar degree (similar to 13%) in both YT rats (18.7 vs. 16.2 N/cm(2)) and OT rats (15.8 vs. 13.7 N/cm(2)). It is concluded that exercise training attenuates the force deficit after repeated lengthening contractions to a comparable extent in young and old rats training at a similar exercise intensity.