Maximal and Submaximal Handgrip Exercise Stimulates Thrombocytosis

Introduction Blood platelets sequester, store, and release a majority of blood‐borne brain‐derived neurotrophic factor (BDNF), which is a major orchestrator of exercise‐induced brain plasticity. Exercise involving large muscle mass transiently increases platelet and serum BDNF levels in an intensity‐dependent manner. During exercise, augmented sympathetic outflow causes splenic contractions, which increases platelet levels in the blood (exercise‐induced thrombocytosis). Interestingly, very brief (60 s) submaximal activation of small muscle mass induces splenic constriction and a 2% elevation in platelet levels. If small muscle exercise is sufficient enough of a stimulus to increase platelet levels, then by extension, it could stand as a viable strategy for increasing BDNF availability; however, the platelet response to dynamic handgrip exercise (HGEX) is currently unknown. Purpose To examine the response of platelets following both short‐duration maximal and prolonged submaximal intensity dynamic HGEX. Methods Healthy males (n = 6; 21.7 ±2.5 yrs old) have been recruited. Exercise protocols were performed on separate days. The high‐intensity exercise was a critical power test (CP), consisting of maximal squeezing for 10 minutes. Submaximal exercise (SE) consisted of HGEX performed at 15% below critical power for 30 minutes. Both protocols used a 2:2 contraction:relaxation duty cycle. Platelets were derived from a complete blood count analysis performed by a haematology lab. Results Platelets increased by 8% from rest to CP (n = 6; 217.9 vs. 236.4 x10 9 /L; p < .05) and 6% from rest to SE (n = 3; 193.3 vs. 206 x10 9 /L, p = .06). Conclusion Preliminary data demonstrate that platelets increase in a similar fashion to HGEX, regardless of exercise intensity.