PMID- 21160000
OWN - NLM
STAT- MEDLINE
DCOM- 20110616
LR  - 20240320
IS  - 1522-1598 (Electronic)
IS  - 0022-3077 (Print)
IS  - 0022-3077 (Linking)
VI  - 105
IP  - 2
DP  - 2011 Feb
TI  - Discharge characteristics of biceps brachii motor units at recruitment when older 
      adults sustained an isometric contraction.
PG  - 571-81
LID - 10.1152/jn.00841.2010 [doi]
AB  - The purpose of this study was to compare the discharge characteristics of motor 
      units recruited during an isometric contraction that was sustained with the elbow 
      flexor muscles by older adults at target forces that were less than the 
      recruitment threshold force of each isolated motor unit. The discharge times of 
      27 single motor units were recorded from the biceps brachii in 11 old adults 
      (78.8 +/- 5.9 yr). The target force was set at either a relatively small (6.6 +/- 
      3.7% maximum) or large (11.4 +/- 4.5% maximum) difference below the recruitment 
      threshold force and the contraction was sustained until the motor unit was 
      recruited and discharged action potentials for about 60 s. The time to 
      recruitment was longer for the large target-force difference (P = 0.001). At 
      recruitment, the motor units discharged repetitively for both target-force 
      differences, which contrasts with data from young adults when motor units 
      discharged intermittently at recruitment for the large difference between 
      recruitment threshold force and target force. The coefficient of variation (CV) 
      for the first five interspike intervals (ISIs) increased from the small (18.7 +/- 
      7.9) to large difference (35.0 +/- 10.2%, P = 0.008) for the young adults, but did 
      not differ for the two target force differences for the old adults (26.3 +/- 14.7 
      to 24.0 +/- 13.1%, P = 0.610). When analyzed across the discharge duration, the 
      average CV for the ISI decreased similarly for the two target-force differences 
      (P = 0.618) in old adults. These findings contrast with those of young adults and 
      indicate that the integration of synaptic input during sustained contractions 
      differs between young and old adults.
FAU - Pascoe, Michael A
AU  - Pascoe MA
AD  - Neurophysiology of Movement Laboratory, Carlson 202G 354 UCB, Department of 
      Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA. 
      pascoe@colorado.edu
FAU - Holmes, Matthew R
AU  - Holmes MR
FAU - Enoka, Roger M
AU  - Enoka RM
LA  - eng
GR  - AG-09000/AG/NIA NIH HHS/United States
GR  - T32 AG-000279-08/AG/NIA NIH HHS/United States
PT  - Comparative Study
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
DEP - 20101215
PL  - United States
TA  - J Neurophysiol
JT  - Journal of neurophysiology
JID - 0375404
SB  - IM
MH  - Adult
MH  - Aged
MH  - Female
MH  - Humans
MH  - Isometric Contraction/*physiology
MH  - Male
MH  - Motor Neurons/*physiology
MH  - Muscle, Skeletal/*physiology
MH  - Recruitment, Neurophysiological/*physiology
PMC - PMC3059164
EDAT- 2010/12/17 06:00
MHDA- 2011/06/17 06:00
PMCR- 2012/02/01
CRDT- 2010/12/17 06:00
PHST- 2010/12/17 06:00 [entrez]
PHST- 2010/12/17 06:00 [pubmed]
PHST- 2011/06/17 06:00 [medline]
PHST- 2012/02/01 00:00 [pmc-release]
AID - jn.00841.2010 [pii]
AID - J00841-10 [pii]
AID - 10.1152/jn.00841.2010 [doi]
PST - ppublish
SO  - J Neurophysiol. 2011 Feb;105(2):571-81. doi: 10.1152/jn.00841.2010. Epub 2010 Dec 
      15.