Presentation Type

Poster

Abstract

Purpose: Since the 1950s investigators focused on the motor control strategies used by the central nervous system to alter the force outputs of skeletal muscle, and have repeatedly observed a highly linear relationship between the forces applied to the environment and the volume of muscle activated to generate this tension. This classical relationship underpins nearly all existing hypotheses on the mechanisms of neuromuscular fatigue, yet it is unknown whether this understanding holds during the activation of fatigued muscle fibers.

Methods: Subjects completed a minimum of 40 exhaustive sprint-running trials (typically 5 trials per lab visit), on a high-speed force treadmill at speeds selected to produce failure between 3 and 300 s. We used a within-trial, blinded, speed change, which either increased or decreased the initial speed by 15%, and measured the level of neuromuscular activity using EMG. Surface electrodes were placed over the muscle bellies of the right medial and lateral gastrocnemii, vastus lateralis and vastus medialis; these data were digitized and recorded at 2000 Hz, and subsequently analyzed in custom written software.

Originality: Neuromuscular responses occurring during the development of fatigue have been well studied; however, there is considerable uncertainty associated with how the body modulates force output in muscle fibers that are contracting dynamically. During the initial contractions that followed the speed increment or decrement, we tested whether the volume of active muscle needed to apply the necessary ground reaction force differed from similar measures obtained at the onset of a running trial (i.e. the fresh condition).

Significance: This study will inform the basic understanding of how the nervous system recruits muscle and how muscle communicates with nerves.

Category

Life Sciences

Available for download on Monday, April 13, 2020

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Apr 15th, 11:00 AM Apr 15th, 12:00 PM

Motor Control of Force Output in Fresh and Fatigued Muscle Fibers

Purpose: Since the 1950s investigators focused on the motor control strategies used by the central nervous system to alter the force outputs of skeletal muscle, and have repeatedly observed a highly linear relationship between the forces applied to the environment and the volume of muscle activated to generate this tension. This classical relationship underpins nearly all existing hypotheses on the mechanisms of neuromuscular fatigue, yet it is unknown whether this understanding holds during the activation of fatigued muscle fibers.

Methods: Subjects completed a minimum of 40 exhaustive sprint-running trials (typically 5 trials per lab visit), on a high-speed force treadmill at speeds selected to produce failure between 3 and 300 s. We used a within-trial, blinded, speed change, which either increased or decreased the initial speed by 15%, and measured the level of neuromuscular activity using EMG. Surface electrodes were placed over the muscle bellies of the right medial and lateral gastrocnemii, vastus lateralis and vastus medialis; these data were digitized and recorded at 2000 Hz, and subsequently analyzed in custom written software.

Originality: Neuromuscular responses occurring during the development of fatigue have been well studied; however, there is considerable uncertainty associated with how the body modulates force output in muscle fibers that are contracting dynamically. During the initial contractions that followed the speed increment or decrement, we tested whether the volume of active muscle needed to apply the necessary ground reaction force differed from similar measures obtained at the onset of a running trial (i.e. the fresh condition).

Significance: This study will inform the basic understanding of how the nervous system recruits muscle and how muscle communicates with nerves.