Acute Effect of Contraction Speed During Motor Imagery on Corticospinal Excitability
Disciplines
Exercise Science | Motor Control
Abstract (300 words maximum)
BACKGROUND: Motor Imagery (MI) is the imagination of a movement without physical muscle contraction. Acute MI has been shown to increase corticospinal excitability, but most studies have used generic instructions with little emphasis on the contraction speed, or rate of torque development (RTD). RTD refers to how quickly skeletal muscle generates torque and is associated with mobility in aging and clinical populations. MI has implications for these populations where traditional strength training may not be possible, so it is important to determine its effect when RTD is emphasized. Corticospinal responses to MI are specific to the task and muscle imagined, but it remains unclear if the speed of the imagined muscle contractions specifically affects neural responses. This study aimed to determine the acute effects of fast and slow imagined contractions on corticospinal excitability. METHODS: As part of an ongoing study, eight young (18-30 yrs), healthy subjects completed 4 laboratory visits in randomized order, including a familiarization session, control, and 2 MI conditions. During the MI conditions, subjects imagined 2 sets of 25 repetitions of either fast (i.e., increase torque as fast as possible) or slow (i.e., 3 seconds to peak torque) isometric elbow flexions. Before and after each condition, single pulses were delivered over the primary motor cortex using transcranial magnetic stimulation to measure motor-evoked potential amplitude in the bicep brachii to quantify changes in corticospinal excitability. Friedman's test was used to examine changes across time in each condition. RESULTS: Corticospinal excitability remained unchanged for each condition (p=0.687). CONCLUSIONS: Our preliminary results suggest that contraction speed during MI does not specifically modulate corticospinal excitability. However, upon obtaining a larger sample size, we will have stronger evidence regarding this effect.
Academic department under which the project should be listed
WCHHS - Exercise Science and Sport Management
Primary Investigator (PI) Name
Garrett Hester
Acute Effect of Contraction Speed During Motor Imagery on Corticospinal Excitability
BACKGROUND: Motor Imagery (MI) is the imagination of a movement without physical muscle contraction. Acute MI has been shown to increase corticospinal excitability, but most studies have used generic instructions with little emphasis on the contraction speed, or rate of torque development (RTD). RTD refers to how quickly skeletal muscle generates torque and is associated with mobility in aging and clinical populations. MI has implications for these populations where traditional strength training may not be possible, so it is important to determine its effect when RTD is emphasized. Corticospinal responses to MI are specific to the task and muscle imagined, but it remains unclear if the speed of the imagined muscle contractions specifically affects neural responses. This study aimed to determine the acute effects of fast and slow imagined contractions on corticospinal excitability. METHODS: As part of an ongoing study, eight young (18-30 yrs), healthy subjects completed 4 laboratory visits in randomized order, including a familiarization session, control, and 2 MI conditions. During the MI conditions, subjects imagined 2 sets of 25 repetitions of either fast (i.e., increase torque as fast as possible) or slow (i.e., 3 seconds to peak torque) isometric elbow flexions. Before and after each condition, single pulses were delivered over the primary motor cortex using transcranial magnetic stimulation to measure motor-evoked potential amplitude in the bicep brachii to quantify changes in corticospinal excitability. Friedman's test was used to examine changes across time in each condition. RESULTS: Corticospinal excitability remained unchanged for each condition (p=0.687). CONCLUSIONS: Our preliminary results suggest that contraction speed during MI does not specifically modulate corticospinal excitability. However, upon obtaining a larger sample size, we will have stronger evidence regarding this effect.