Effects of Acute Exercise and Training on the Sarcoplasmic Reticulum Ca Release and Uptake Rates in Highly Trained Endurance Athletes.

Little is presently known about the effects of acute high-intensity exercise or training on release and uptake of Ca by the sarcoplasmic reticulum (SR). The aims here were to characterize this regulation in highly trained athletes following (1) repeated bouts of high-intensity exercise and (2) a period of endurance training including high-intensity sessions. Eleven cross-country skiers (25 ± 4 years, 65 ± 4 mL O⋅kg⋅min) performed four self-paced sprint time-trials (STT 1-4) lasting ≈ 4 min each (STT 1-4) and separated by 45 min of recovery; while 19 triathletes and road cyclists (25 ± 4 years, 65 ± 5 mL O⋅kg⋅min) completed 4 weeks of endurance training in combination with three sessions of high-intensity interval cycling per week. Release (μmol⋅g prot⋅min) and uptake [tau (s)] of Ca by SR vesicles isolated from m. and m. were determined before and after STT 1 and 4 in the skiers and in m. before and after the 4 weeks of training in the endurance athletes. The Ca release rate was reduced by 17-18% in both limbs already after STT 1 (arms: 2.52 ± 0.74 to 2.08 ± 0.60; legs: 2.41 ± 0.45 to 1.98 ± 0.51, < 0.0001) and attenuated further following STT 4 (arms: 2.24 ± 0.67 to 1.95 ± 0.45; legs: 2.13 ± 0.51 to 1.83 ± 0.36, < 0.0001). Also, there was a tendency toward an impairment in the SR Ca uptake from pre STT1 to post STT4 in both arms and legs (arms: from 22.0 ± 3.7 s to 25.3 ± 6.0 s; legs: from 22.5 ± 4.7 s to 25.5 ± 7.7 s, = 0.05). Endurance training combined with high-intensity exercise increased the Ca release rate by 9% (1.76 ± 0.38 to 1.91 ± 0.44, = 0.009), without altering the Ca uptake (29.6 ± 7.0 to 29.1 ± 8.7 s; = 0.98). In conclusion, the Ca release and uptake rates by SR in exercising limbs of highly trained athletes declines gradually by repetitive bouts of high-intensity exercise. We also demonstrate, for the first time, that the SR Ca release rate can be enhanced by a specific program of training in highly trained athletes, which may have important implications for performance parameters.