It's not what you do, it's how hard you do it

The poster session today was dominated by all things motor. A paper that caught my eye was presented by K Leech [presentation #74.05]. We accept that rehabilitation has an important part to play in recovery from SCI but how much is optimal and for how long should it be given?

Animal studies have shown that high intensity rehab increases the amount of a neurotrophic factor called brain derived neurotrophic factor, or BDNF, which is associated with improved recovery of stepping. BDNF is a potent promoter of neurite growth, has neuroprotective activity, can enhance plasticity and even give rise to re-myelination (see Weishaupt et al, Exp Neurol, 2012). It is actively being researched as a possible candidate treatment for SCI. Exercise is known to cause changes in BDNF levels in the periphery and in the central nervous system.

Leech’s findings are important because they shed a little light on the possible mechanisms by which BDNF might be beneficially modulated in patients with SCI. Leech and colleagues monitored the level of BDNF in the blood and compared levels after various regimes of rehabilitation exercise. They found that only high-intensity exercise elevated BDNF levels whilst low to moderate levels had no effect. Increasing the duration of moderate exercise didn’t change matters either suggesting that a threshold of intensity is needed for that all important hit of the neurotrophin.

Future studies will look at whether the increase in BDNF is related positively to better outcomes in patients. Interestingly, some patients studied had a common genetic variation which means for them it is harder to achieve elevated BDNF levels and their BDNF response to high-intensity exercise was “blunted”. Such understanding might lead to better rehab regimes tailored to the individual for optimal neurological effect.