PMID- 26251512
OWN - NLM
STAT- MEDLINE
DCOM- 20160713
LR  - 20161125
IS  - 1522-1601 (Electronic)
IS  - 0161-7567 (Linking)
VI  - 119
IP  - 7
DP  - 2015 Oct 1
TI  - Doublet potentiation in the triceps surae is limited by series compliance and 
      dynamic fascicle behavior.
PG  - 807-16
LID - 10.1152/japplphysiol.00403.2015 [doi]
AB  - Activation of skeletal muscle twice in quick succession results in nonlinear 
      force summation (i.e., doublet potentiation). The force contributed by a second 
      activation is typically of augmented amplitude, longer in duration, and generated 
      at a greater rate. The purpose of this study was to examine force summation in a 
      muscle attached to a compliant tendon, where considerable internal shortening 
      occurs during a fixed-end contraction. The triceps surae of 21 (Experiment 1) and 
      9 (Experiment 2) young adults were maximally activated with doublet stimulation 
      of different interstimulus intervals (ISIs) (5-100 ms) at several muscle lengths. 
      Ultrasound images acquired from lateral gastrocnemius and soleus muscles allowed 
      quantification of dynamic fascicle behavior. Force summation was muscle length 
      dependent. Force augmentation was limited to a short muscle length. Lateral 
      gastrocnemius and soleus fascicles underwent large amounts of active shortening 
      and achieved high velocities in response to doublet stimulation, dynamics 
      unfavorable for force production. Summation amplitude and the sensitivity of 
      summation to ISI were dramatically depressed in the triceps surae after 
      comparison to muscles with less fixed-end compliance. We propose that the 
      internal shortening permitted by high series compliance limited force 
      augmentation by offsetting and/or interfering with activation and cross-bridge 
      processes driving augmentation. High series compliance may also reduce the 
      sensitivity of the summated response to ISI, an assertion supported by 
      predictions from a Hill-type muscle model. These muscles may exhibit greater 
      force augmentation during more accustomed stretch-shorten tasks (i.e., hopping), 
      where the compliance of the Achilles tendon actually enables near-isometric 
      fascicle behavior.
CI  - Copyright (c) 2015 the American Physiological Society.
FAU - Mayfield, Dean L
AU  - Mayfield DL
AUID- ORCID: 0000-0003-4036-7117
AD  - School of Human Movement and Nutrition Sciences, The University of Queensland, 
      Brisbane, Australia;
FAU - Lichtwark, Glen A
AU  - Lichtwark GA
AD  - School of Human Movement and Nutrition Sciences, The University of Queensland, 
      Brisbane, Australia;
FAU - Cronin, Neil J
AU  - Cronin NJ
AD  - Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, 
      Finland.
FAU - Avela, Janne
AU  - Avela J
AD  - Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, 
      Finland.
FAU - Cresswell, Andrew G
AU  - Cresswell AG
AD  - School of Human Movement and Nutrition Sciences, The University of Queensland, 
      Brisbane, Australia; a.cresswell@uq.edu.au.
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20150806
PL  - United States
TA  - J Appl Physiol (1985)
JT  - Journal of applied physiology (Bethesda, Md. : 1985)
JID - 8502536
SB  - IM
MH  - Achilles Tendon/physiology
MH  - Biomechanical Phenomena
MH  - Compliance/physiology
MH  - Electric Stimulation
MH  - Electromyography
MH  - Female
MH  - Humans
MH  - Isometric Contraction/physiology
MH  - Knee Joint/physiology
MH  - Leg/diagnostic imaging/physiology
MH  - Male
MH  - Muscle Contraction/physiology
MH  - Muscle, Skeletal/diagnostic imaging/*physiology
MH  - Peripheral Nerves/physiology
MH  - Tendons/physiology
MH  - Torque
MH  - Ultrasonography
MH  - Young Adult
OTO - NOTNLM
OT  - force summation
OT  - muscle force
OT  - muscle mechanics
OT  - muscle-tendon interaction
EDAT- 2015/08/08 06:00
MHDA- 2016/07/14 06:00
CRDT- 2015/08/08 06:00
PHST- 2015/05/26 00:00 [received]
PHST- 2015/08/03 00:00 [accepted]
PHST- 2015/08/08 06:00 [entrez]
PHST- 2015/08/08 06:00 [pubmed]
PHST- 2016/07/14 06:00 [medline]
AID - japplphysiol.00403.2015 [pii]
AID - 10.1152/japplphysiol.00403.2015 [doi]
PST - ppublish
SO  - J Appl Physiol (1985). 2015 Oct 1;119(7):807-16. doi: 
      10.1152/japplphysiol.00403.2015. Epub 2015 Aug 6.