Muscle-specific glucose and free fatty acid uptake after sprint interval and moderate-intensity training in healthy middle-aged men.

We tested the hypothesis that sprint interval training (SIT) causes larger improvements in glucose and free fatty acid uptake (FFAU) in lower and upper body muscles than moderate-intensity training (MIT). Twenty-eight healthy, untrained, middle-aged men were randomized into SIT (n = 14, 4-6 × 30 s of all-out cycling/4 min recovery) and MIT groups [n = 14, 40-60 min cycling at 60% of peak O2 uptake (V̇o2 peak)] and completed six training sessions within 2 wk. Pre- and postmeasurements included V̇o2 peak, whole body (M-value), muscle-specific insulin-stimulated glucose uptake (GU), and fasting FFAU measured with positron emission tomography in thigh [quadriceps femoris (QF) and hamstrings] and upper body (deltoids, biceps, and triceps brachii) muscles. V̇o2 peak and M-value improved significantly by 6 and 12% in SIT, and 3 and 8% in MIT, respectively,. GU increased significantly only in the QF, and there was no statistically significant difference between the training modes. GU increased in all four heads of QF in response to SIT, but only in the vasti muscles in response to MIT, whereas in rectus femoris the response was completely lacking. Training response in FFAU in QF was smaller and nonsignificant, but it also differed between the training modes in the rectus femoris. In conclusion, SIT and MIT increased insulin-stimulated GU only in the main working muscle QF and not in the upper body muscles. In addition, the biarticular rectus femoris did not respond to moderate-intensity training, reflecting most probably poor activation of it during moderate-intensity cycling.