Focal knee joint cooling increases the quadriceps central activation ratio.

The objective of this study was to evaluate the effects of a 20-min focal knee joint cooling intervention on quadriceps central activation ratio (CAR) in healthy volunteers. A counterbalanced, cross-over study assessed the effects of a focal joint cooling intervention compared with a control condition 3-14 days apart. Eleven healthy volunteers (6 males, 5 females; age 25 +/- 5 years; height 1.71 +/- 0.1 m, mass 77 +/- 21 kg) were included in the final analysis. The joint cooling intervention consisted of two 1.5-litre ice bags applied to the knee joint for 20 min, in one of two counterbalanced sessions, completed 3-14 days apart. In the control session, participants sat quietly between the baseline and 20-min measurements. Quadriceps CAR was assessed at 70 degrees of knee flexion at four instants (baseline, 20, 30, and 45 min). There was a significant treatment x time interaction (F(3,30) = 5.9, P = 0.003) and post hoc analyses revealed that CAR was higher in the focal knee joint cooling session than the control session at 20 min (0.79 +/- 0.12 vs. 0.70 +/- 0.12; t(10) = 3.9, P = 0.003) and 45 min (0.77 +/- 0.10 vs. 0.69 +/- 0.12; t(10) = 3.1, P = 0.01). The CAR tended to be higher during the experimental session than the control session at 30 min (0.79 +/- 0.13 vs. 0.74 +/- 0.11; t(10) = 2.1, P = 0.07).Volitional activation increased following focal knee joint cooling in healthy volunteers.