Impact of endurance concentric contraction training on acute force deficit following in vitro lengthening contractions

Abstract

The purposes of this study were to (1) determine whether endurance training employing solely concentric contractions would reduce force deficit following lengthening contractions, and (2) to determine if aged skeletal muscle would respond similarly from training, compared with young animals. Young (3-month) and old (23-month) male Fischer 344 rats were randomly assigned to either a control or an exercise training group. Exercise training consisted of 10 weeks of treadmill running (15% grade, 45 min/day, and 5 days/week) such that by the end of training the young and old rats were exercising at 27 and 15 m/min, respectively (approximately 70% ). After training, the percent decrease in maximal isometric force ( P(o)) of the diaphragm muscle was measured in vitro at 26 degrees C immediately after a series of 20 lengthening contractions (20% strain from optimal muscle length, one contraction every 5 s), and at 5 and 10 min post-injury. At 10 min post-injury, P(o) averaged approximately 66% of initial P(o) in the exercise group (young and old combined) and approximately 61% of initial P(o) in the control groups (young and old combined) ( P<0.05). This difference represents an attenuation of force deficit by approximately 13% in the trained animals, compared with controls. These findings indicate that 10 weeks of endurance training employing solely concentric contractions is beneficial in minimizing acute force deficit after a bout of lengthening contractions in both young and old rats.

Wheel-running exercise alters rat diaphragm action potentials and their regulation by K+ channels

“…Third, the Hughes and Gosselin study used a 15% grade, and it would appear that Vrabas et al (41) did as well, whereas the grade is hard to quantify with wheel running (but is probably less). Fourth, in Hughes and Gosselin (14) study animals exercised continuously for 45 min, and in the Vrabas et al (41) study the exercise was accomplished over the course of 60 min, whereas in the present study the exercise was intermittent but spread out over the course of the animals' waking hours.…”

“…Vrabas et al (41) did not specify the exact mileage for their animals, but they stated the animals ran for 60 min/day and then referenced the protocol of Metzger and Fitts (26), which used 40 m/min, 27 min/day, 5 day/wk, or 5,400 m/wk (so even if doubled this amounts to 10,800 m/wk). In the present study, during the last several weeks the animals ran ϳ10,000 m/day or ϳ70,000 m/wk, a weekly distance that is 10-fold longer than in the Hughes and Gosselin (14) study. Third, the Hughes and Gosselin study used a 15% grade, and it would appear that Vrabas et al (41) did as well, whereas the grade is hard to quantify with wheel running (but is probably less).…”

“…Second, the distance run per week was longer in the present compared with previous studies. Hughes and Gosselin (14) had their (young) animals run 27 m/min, 45 min/day, 5 days/wk by the end of the training period; this amounts to 6,075 m/wk. Vrabas et al (41) did not specify the exact mileage for their animals, but they stated the animals ran for 60 min/day and then referenced the protocol of Metzger and Fitts (26), which used 40 m/min, 27 min/day, 5 day/wk, or 5,400 m/wk (so even if doubled this amounts to 10,800 m/wk).…”

Determinants of the Repeated-Bout Effect After Lengthening Contractions

“…Studies of the volume and intensity of exercise, type of contraction, and magnitude of muscle strain have provided evidence that the RBE can be induced by a brief exposure to lengthening contractions that result in an immediate and significant (~50%) loss of contractile function. While training with concentric contractions prior to a bout of lengthening contractions makes the muscle more susceptible to contraction-induced injury in humans 13 , it produces a RBE in old and young rats 27, 28 . Both passive stretches and isometric contractions offer some protection against later injury with little risk of muscle damage.…”