NEURAL CONTROL OF ECCENTRIC AND POST- ECCENTRIC MUSCLE ACTIONS 1, 2 Daniel Hahn, 1 Ben W. Hoffman, 1 Timothy J. Carroll and 1 Andrew G. Cresswell 1 School of Human Movement Studies, University of Queensland, Brisbane, Australia 2 Department of Biomechanics in Sports, Faculty of Sport & Health Science, Technische Universität München, Germany
Muscle action during and after stretch during stretch: unique control strategies associated with neural inhibition (Westing 1991) mainly on the spinal level l (Gruber et al. 2009, Duclay et al. 2011) in both studies subjects failed to produce higher force/torque during stretch after stretch: higher forces after muscle stretch Residual Force Enhancement (RFE) (Abbott & Aubert 1952, Leonard et al. 2010, Hahn et al. 2010) currently no studies on neural control strategies Aim: Investigation of neural control strategies in the enhanced state during and after stretch
Methods & Experimental protocol calf muscles of n = 10 healthy subjects (29.1 ± 6.6 yr, 1.77 ± 0.08 m and 73.4 ± 11.8 kg) Biodex, System 3, USA - movement control - ankle joint torque EMG of mm. soleus (SOL), medial gastrocnemius (MG) and tibialis anterior (TA) - background activity (BGA) - muscle responses to different stimulation types
Methods & Experimental protocol 1 training session, 1 test session 3 different maximum voluntary plantar flexor contractions: - isometric MVCs @ 10 and 20 dorsal extension (reference contractions) - isometric-eccentric-isometric MVCs with a stretch from neutral position (0 ) to 20 dorsal extension @ 30 s -1 (referred to as stretch contraction) 3 different types of superimposed stimulation during and after stretch: - electrical nerve stimulation (ENS) of the tibial nerve - electrical stimulation of the cervicomedullary junction (CMS) spinal pathways - transcranial magnetic stimulation (TMS) of the motor cortex corticospinal pathways random order of stimulation types and corresponding contractions minimum of 3 min rest
Data analysis & Statistics @ 2 instances in time: during stretch (stim1) and after stretch (stim2) - Torque @ time of stimulation (stim1), i.e. at the same joint angle for isometric and stretch MVCs and over a 500ms window prior to stimulation (stim2), i.e. 2.5-3 seconds after stretch. - EMG over a 50ms window prior to stim1 and 500 ms prior to stim2; (RMS amplitude). FE stim1 RFE stim2
Data analysis & Statistics - Size of muscle responses to single pulse stimulations @ stim1 and stim2 (Peak-to-peak amplitude and area) M-wave &V V-wave (ENS) cervicomedullary evoked potential CMEP (CMS) motor evoked potential MEP (TMS) FE stim1 RFE stim2 Statistics - Kolmogorov Smirnov testt - two way repeated ANOVA with Bonferroni Holm post hoc comparisons - paired student t-tests; alpha level p.05.
Results Torque during (FE) and after stretch (RFE) - lengthening of MG during stretch on the ascending limb of the F-l-r - FE of 16.6 ± 7.9 % (mean ± SD), max: 38.9 %, min: 7.3 % - RFE of 9.3 ± 8.4 % (mean ± SD), max: 38.5 %, min: 0.9 %
Results Muscle responses during stretch no changes in M-waves, V-waves and MEPs smaller size of CMEPs for SOL muscle reduced spinal and greater cortical excitability during stretch Normalised size ± SD muscle response SOL MG M-wave 103± 1.03.06 098± 0.98.07 V-wave 1.17 ±.51 1.02 ±.27 MEP 1.03 ±.19 1.08 ±.22 CMEP 0.88 ±.16* 0.92 ±.31
Results Muscle responses after stretch no changes in M-waves and CMEPs increased size of MEPs from SOL & MG muscles and of SOL V-waves greater cortical excitability Normalised size ± SD muscle response SOL MG M-wave 099± 0.99.09 098± 0.98.10 V-wave 1.47 ±.50* 1.22 ±.45 MEP 1.14 ±.15* 1.24 ±.17** CMEP 0.98 ±.16 1.15 ±.51
Conclusion enhanced torque during and following maximal voluntary eccentric contractions during stretch: reduced spinal excitability and/or disfacilitation greater cortical excitability to counteract spinal inhibition (Gruber et al. 2009) different behaviour of SOL and MG muscles (Duclay et al. 2011) after stretch: maintenance of greater cortical excitability phenomenon of RFE is not only based on muscle mechanical properties but also on neural control
Acknowledgements: This research was funded by the Thanks to Ms Simranjit Sidhu and Dr Glen Lichtwark for their helping hands! Thanks for your Attention! TU Munich Sports Campus