Department of Integrative Physiology
University of Colorado
Boulder, CO 80309-0354
phone: 303-492-4965
fax: 303-492-6778
Research Interests
The neuromuscular mechanisms that mediate the acute adjustments and chronic adaptations experienced by humans in response to physical activity. Current projects address two main topics:
Muscle fatigue - identifying the mechanisms responsible for differences in the time to failure for similar tasks.
Aging - characterizing changes in the behavior of motor units and the contribution of these adaptations to the decline in fine motor control experienced by older adults.
Back row (L to R): Adam Marmon, Jeff Gould, Mark Jesunathadas, Matt Holmes, Stéphane Baudry, Thorsten Rudroff, Martin Bækgaard, Kim Jordan; Middle row: Mike Pascoe, Lauren Pierpoint, Jamie Justice, Mike Gibb, Derek Sarchet; Front row: Stephen Matthews, Adam Maerz, Beth Hewes, Jakob Dideriksen.
Current Research Projects
Fatigue-Related Modulation of Motor Unit Discharge Rate (Rudroff, Jordan). To characterize the effect of load type on the decline in motor unit discharge when the arm is placed in different positions.
Motor Unit Discharge During Long Contractions (Pascoe, Holmes). To sustain the discharge of single motor units in a hand muscle of young and old adults for as long as possible.
Functional Correlates of Steadiness (Marmon, Pascoe). To examine the associations between the strength, steadiness, and functional capabilities of hand muscles.
Muscle Mass Involved in Fatiguing Contractions (Rudroff, Kalliokoski, Bojsen-Møller). To use positron emission tomography to compare the amount of muscle mass activated during the force and position tasks.
Recruitment Threshold During Fatiguing Contractions (Baudry, Rudroff). To compare the change in recruitment threshold of motor units during fatiguing contractions with the force and position tasks.
Motor Units in Tibialis Anterior (Jesunathadas, Klass, Duchateau). To compare experimental and simulated values for steadiness across the operating range of the tibialis anterior muscle.
Work Performed During Fatiguing Contractions (Rudroff, Justice). To measure the work performed by the elbow flexor muscles during the force and position tasks.
Force Fluctuations During Steady Contractions (Jordan, Jesunathadas). To characterize the force fluctuations during steady submaximal contractions performed by young and old adults.
Motor Unit Recruitment During Fatiguing Contractions in Old Adults (Pascoe, Holmes). To determine the discharge characteristics of newly recruited motor units in biceps brachii when old adults sustain an isometric contraction.
Recruitment Range in Young and Old Adults (Jesunathadas, Marmon). To determine the influence of age on the distribution of motor unit recruitment thresholds in the first dorsal interosseus muscle.
Presynaptic Inhibition During Fatiguing Contractions (Baudry, Jordan). To compare the level of presynaptic inhibition during the force and position tasks.
Practice and the Interaction Between Dexterity and Steadiness (Marmon, Gould). To evaluate the influence of practicing a task of manual dexterity on steadiness.
Visual Gain and Discharge Variability (Jordan, Maerz). To assess the influence of varying visual information on motor unit discharge and steadiness during a functional task.
Opportunities for Undergraduates
The requirements for undergraduate students who want a research experience in our Laboratory are:
A major in integrative physiology
Either have completed or be concurrently enrolled in IPHY 4720 (Neurophysiology)
Obtain UROP funding or enroll in independent study (IPHY 4860) for 8-10 hours/week for at least one semester.
For more information, contact Mark Jesunathadas (mark.jesunathadas@colorado.edu)
Recent Publications
Barry BK, Pascoe MA, Riek S, Carson RG, Enoka RM. Common input to different regions of biceps brachii long head. Experimental Brain Research 193: 351-359, 2009.
Baudry S, Jordan K, Enoka RM. Heteronymous reflex responses in a hand muscle when maintaining constant finger force or position at different contraction intensities. Clinical Neurophysiology 120: 210-217, 2009.
Duchateau J, Enoka RM. Neural control of shortening and lengthening contractions: influence of task constraints. Journal of Physiology 24: 5853-5864, 2008.
Enoka RM, Duchateau J. Muscle fatigue: what, why and how it influences muscle function. Journal of Physiology 586: 11-23, 2008.
Farina D, Holobar A, Gazzoni M, Zazula D, Merletti R, Enoka RM. Adjustments differ among low-threshold motor units during intermittent, isometric contractions. Journal of Neurophysiology 101: 350-359, 2009.
Poston B, Enoka JA, Enoka RM. Endpoint accuracy for a small and a large hand muscle in young and old adults during rapid, goal-directed isometric contractions. Experimental Brain Research 187: 373-385, 2008.
Riley ZA, Baudry S, Enoka RM. Reflex inhibition in human biceps brachii decreases with practice of a fatiguing contraction. Journal of Neurophysiology 100: 2843-2851, 2008.
Riley ZA, Maerz AH, Litsey JC, Enoka RM. Motor unit recruitment in human biceps brachii during sustained voluntary contractions. Journal of Physiology 586: 2183-2193, 2008.
Funding
1990-2010, NIH R01 AG09000, "Steadiness in Older Adults"
2002-2009, NIH R01 NS43275, "Neural Mechanisms of Muscle Fatigue"
