Faculty Collaboration Database

Differential effects of aging and physical activity on corticospinal excitability of upper and lower limb muscles. J Neurophysiol 2019 Jul 01;122(1):241-250

Date

05/16/2019

Pubmed ID

31091158

Pubmed Central ID

PMC6689774

DOI

10.1152/jn.00077.2019

Scopus ID

2-s2.0-85069235071 (requires institutional sign-in at Scopus site)   21 Citations

Abstract

Corticospinal tract excitability can be altered by age, physical activity (PA), and possibly sex, but whether these effects differ between upper and lower limb muscles is unknown. We determined the influence of age, PA, and sex on corticospinal excitability of an upper limb and a lower limb muscle during submaximal contractions by comparing stimulus-response curves of motor evoked potentials (MEPs). Transcranial magnetic stimulation (TMS) was used to evoke stimulus-response curves in active muscles by incrementally increasing the stimulator intensity from below the active motor threshold (AMT) until a plateau in MEP amplitudes was achieved. Stimulus-response curves were analyzed from the first dorsal interosseous (FDI) of 30 young (23.9 ± 3.8 yr) and 33 older (72.6 ± 5.6 yr) men and women and the vastus lateralis (VL) of 13 young (23.2 ± 2.2 yr) and 25 older (72.7 ± 5.5 yr) men and women. Corticospinal excitability was determined by fitting the curves with a four-parameter sigmoidal curve and calculating the maximal slope (slope_max). PA was assessed with triaxial accelerometry, and participants were dichotomized into high-PA (>10,000 steps/day, n = 15) or low-PA (<10,000 steps/day, n = 43) groups. Young adults had larger FDI MEP amplitudes (% maximum amplitude of compound muscle action potential) at higher TMS intensities (120-150% AMT) and greater slope_max than older adults (P < 0.05), with no differences between high- and low-PA groups (P > 0.05). VL MEP amplitudes and slope_max, however, were lower in the high-PA than low-PA participants, with no age or sex differences. These data suggest that aging and PA, but not sex, differentially influence the excitability of the corticospinal tracts projecting to muscles of the upper compared with the lower limb. NEW & NOTEWORTHY Excitability of the corticospinal tract projecting to the first dorsal interosseous assessed with transcranial magnetic stimulation was reduced with age but independent of regular physical activity (steps/day) and sex of the individual. In contrast, corticospinal excitability of the vastus lateralis was not affected by age but was reduced in individuals achieving more than the physical activity recommendations of 10,000 steps/day. Aging and activity differentially affect corticospinal excitability of upper and lower limb muscles.

Author List

Rozand V, Senefeld JW, Sundberg CW, Smith AE, Hunter SK

Author

Chrisopher Sundberg in the CTSI department at Medical College of Wisconsin - CTSI

MESH terms used to index this publication - Major topics in bold

Adult
Aged
Aged, 80 and over
Aging
Evoked Potentials, Motor
Exercise
Extremities
Female
Humans
Male
Muscle, Skeletal
Pyramidal Tracts