NEURAL CONTROL OF ECCENTRIC AND POST- ECCENTRIC MUSCLE ACTIONS

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1 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

2 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

3 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

4 Methods & Experimental protocol 1 training session, 1 test session 3 different maximum voluntary plantar flexor contractions: - isometric 10 and 20 dorsal extension (reference contractions) - isometric-eccentric-isometric MVCs with a stretch from neutral position (0 ) to 20 dorsal 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

5 Data analysis & 2 instances in time: during stretch (stim1) and after stretch (stim2) - 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 seconds after stretch. - EMG over a 50ms window prior to stim1 and 500 ms prior to stim2; (RMS amplitude). FE stim1 RFE stim2

6 Data analysis & Statistics - Size of muscle responses to single pulse 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.

7 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 %

excitability during stretch Normalised size ± SD muscle response SOL MG M-wave 103±

8 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± ± V-wave 1.17 ± ±.27 MEP 1.03 ± ±.22 CMEP 0.88 ±.16* 0.92 ±.31

9 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± ± V-wave 1.47 ±.50* 1.22 ±.45 MEP 1.14 ±.15* 1.24 ±.17** CMEP 0.98 ± ±.51

10 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

11 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

Is there inhibition during eccentric muscle contractions?

Is there inhibition during eccentric muscle contractions? Biomechanics of Human Movement: Mechanisms and Methods position 17th International Symposium Neuromuscular Research Center (NMRC) University of Jyväskylä Moment EMG VL EMG VM EMG RF Is there inhibition