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Low-frequency fatigue increases with the number of stretches of activated rat skeletal muscles.
Willems MET; Stauber WT
Med Sci Sports Exerc 2003 May; 35(5)(Suppl 1):S144
To examine the relationship between stretch number of activated plantar flexor muscles and low-frequency fatigue. In female Sprague Dawley rats (age 3-5 mo), nerve stimulation was used to produce muscle contractions. Stretches [3 stretches (S), 10S, 60S or 240S (n = 6 in each group)] were imposed on isometric contractions [80 Hz, 0.2 ms pulse duration, 5.3 +/- 0.3 V (mean +/- SE)] by ankle rotation from 90 degrees to 40 degrees (velocity: 600 ·s-1, simulation time: 0.9 s, inter-stretch rest time: 40 s). Forty seconds after the last stretch, an isometric contraction (80 Hz at 90 degrees) was performed. Force-frequency relationships with isometric contractions at 90 degees were measured before and 1 hour after the stretch protocols. An index for low-frequency fatigue was calculated by the change in the 20:100 Hz isometric force ratio. All stretch protocols resulted in isometric force deficits (3S: 37.0 +/- 2.4%, 10S: 44.6 +/- 1.5%, 60S: 74.1 +/- 1.9%, 240S: 83.4 +/- 2.0%). After 1 hour, substantial deficits remained (3S: 33.3 +/- 1.7%, 10S: 37.2 +/- 2.3%, 60S: 67.6 +/- 1.5%, 240S: 77.7 +/- 1.2%) and low-frequency fatigue was present in all groups. Force deficits with contractions at 20 Hz were significantly larger than at 100 Hz (3S: 45.9 +/- 2.4% vs. 30.8 +/- 2.0%, 10S: 57.1 +/- 3.0% vs. 34.2 +/- 2.1%, 60S: 78.9 +/- 0.4% vs. 63.0 +/- 1.7%, 240S: 88.5 +/- 1.3% vs. 73.9 +/- 1.4%). Low-frequency fatigue became significantly larger with an increase in the number of stretches (P = 0.0009). The amount of low-frequency fatigue was related to the number of stretches of activated skeletal muscles providing indirect evidence for an increased failure of excitation-contraction coupling with stretch number.
Muscles; Musculoskeletal system; Skeletal system; Injuries; Muscle tissue; Injury prevention; Musculoskeletal system disorders; Diseases; Laboratory animals; Animals; Animal studies; Fatigue
Issue of Publication
Disease and Injury: Musculoskeletal Disorders of the Upper Extremities
Medicine and Science in Sports and Exercise
West Virginia University, Morgantown, West Virginia
Page last reviewed: April 9, 2021
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