Fatigue and recovery at long and short muscle lengths after eccentric training.
OBJECTIVE
To determine the effects of high-speed eccentric training of rat plantar flexor muscles on: 1) maximum (120 Hz) force at 90 degrees ankle position; 2) fatigue (40 concentric muscle actions, ROM 50 degrees) and recovery (6 concentric muscle actions) tested at short or long muscle lengths; and 3) low-frequency fatigue.


METHODS
Training consisted of eccentric muscle actions from ankle positions of 140 degrees to 40 degrees (velocity approximately 400 degrees x s(-1)) followed by unresisted concentric muscle actions (5 x 10 repetitions, 5 d x wk(-1) for 6 wk). Fatigue was induced by concentric muscle actions with a rest of 12.5 s between muscle actions, and recovery consisted of equivalent concentric muscle actions performed every 5 min for 30 min. Low-frequency fatigue was measured 35 min after testing at 90 degrees ankle position by using the ratio of isometric force produced by 20- and 100-Hz stimulation frequencies.


RESULTS
Eccentric training increased maximal isometric force per muscle weight by 22% whereas muscle weights were unchanged. In control muscles (C), isometric force immediately preceding each concentric muscle action decreased more at long lengths than at short lengths during the fatigue protocol; this length-dependent difference disappeared after 30 min of recovery. At short lengths, isometric force decreased less in trained muscles (T) (C: 78.4 +/- 3.6%; T: 59.6 +/- 4.4%) and recovered more during the following 30-min period (C: 84.7 +/- 2.5%; T: 95.4 +/- 2.8% of initial values). Changes in F20/F100 were smaller for trained muscles (C: 35.4 +/- 2.0%; T: 22.0 +/- 1.4%).


CONCLUSIONS
High-speed eccentric training (5 d x wk(-1) for 6 wk) reduced fatigability and enhanced recovery mainly at long muscle lengths. It also reduced low-frequency fatigue, which may be attributed to alterations in intracellular calcium handling.
Willems
Mark E T
ME
Department of Physiology and Pharmacology, West Virginia University, Morgantown, 26506-9229, USA. mwillems@hsc.wvu.edu
Stauber
William T
WT
D000222:Adaptation, Physiological; D000818:Animals; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D007537:Isometric Contraction / Q000502:physiology; D023421:Models, Animal; D009119:Muscle Contraction; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010805:Physical Conditioning, Animal; D005082:Physical Exertion; D011336:Probability; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012680:Sensitivity and Specificity