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Spinal Mechanisms Contributing To Rate Of Force Development: 2706Board #100 May 29 3:30 PM - 5:00 PM

Johnson, Sam; Kipp, Kristof; Yun, Joonkoo; Hoffman, Mark FACSM

Medicine & Science in Sports & Exercise: May 2009 - Volume 41 - Issue 5 - p 434
doi: 10.1249/01.MSS.0000355871.66248.d0
F-27 Free Communication/Poster- Neural Control of Movement II: MAY 29, 2009 1:00 PM- 6:00 PM ROOM: Hall 4F

Oregon State University, Corvallis, OR.

(No relationships reported)

The neuromuscular system's ability to quickly generate force is important during fast movements and injury prevention. Rate of force development (RFD) is a common measure of this ability. However, it is unknown to what extent spinal control mechanisms contribute to RFD.

PURPOSE: To identify contributions of spinal control mechanisms to RFD.

METHODS: RFD of isometric plantarflexion was measured from 37 participants (19 male and 18 females) on a Biodex System 3 dynamometer with the ankle of the dominant leg secured at 90°. H-reflex, intrinsic pre-synaptic inhibition (IPI), and extrinsic pre-synaptic inhibition (EPI) recruitment curves were obtained from the soleus. IPI testing used the paired pulse conditioning protocol where two stimuli are delivered to the tibial nerve at the same intensity 100 ms apart. EPI was assessed through common peroneal nerve conditioning with 100 ms between the conditioning and test reflexes. Recurrent inhibition (RI), a form of post-synaptic inhibition, was assessed by setting stimulus 1 (S1) to 25% of Mmax and stimulus 2 (S2) to Mmax. Ten trials of both S1 alone and S1 followed 10 ms later by S2 were counterbalanced. Neural drive (Vmax:Mmax) was assessed by a Mmax stimulation to the tibial nerve during an isometric maximum voluntary contraction (iMVC) of the soleus. Five trials with 60 seconds rest between each were collected. Additionally, three trials of iMVC with 60 seconds rest between each were collected to assess RFD. Standard multiple regression was used to determine the contribution of the independent variables to RFD. The independent variables were sex, the first derivative of the H-reflex, IPI, and EPI, RI (S1+S2/ S1), and Vmax:Mmax.

RESULTS: The regression analysis revealed the model significantly predicted RFD (r2 = 0.643, p < 0.001). The significant independent variables were sex (b = -0.564, p < 0.001), V-wave (b = 0.502, p = 0.001), and IPI (b = -0.450, p = 0.016).

CONCLUSION: Sex was a significant contributor, with males having greater RFD. Increased Vmax:Mmax also significantly contributed. IPI, a measure of influence of reflex activation history and thought to reflect modulation of 1a afferent inflow from the muscle spindles significantly contributed to RFD. Based on the results, RFD is a result of increased neural drive, modulation of muscle spindle feedback, and sex differences.

© 2009 American College of Sports Medicine