Reduced volume and increased training intensity elevate muscle Na⁺-K⁺pump α₂-subunit expression as well as short- and long-term work capacity in humans

Abstract

The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners as a result of a reduced amount of training combined with speed endurance training. For a 6- to 9-wk period, 17 runners were assigned to either a speed endurance group with a 25% reduction in the amount of training but including speed endurance training consisting of six to twelve 30-s sprint runs 3-4 times/wk (SET group n = 12) or a control group (n = 5), which continued the endurance training ( approximately 55 km/wk). For the SET group, the expression of the muscle Na(+)-K(+) pump alpha(2)-subunit was 68% higher (P < 0.05) and the plasma K(+) level was reduced (P < 0.05) during repeated intense running after 9 wk. Performance in a 30-s sprint test and the first of the supramaximal exhaustive runs was improved (P < 0.05) by 7% and 36%, respectively, after the speed endurance training period. In the SET group, maximal O(2) uptake was unaltered, but the 3-km (3,000-m) time was reduced (P < 0.05) from 10.4 +/- 0.1 to 10.1 +/- 0.1 min and the 10-km (10,000-m) time was improved from 37.3 +/- 0.4 to 36.3 +/- 0.4 min (means +/- SE). Muscle protein expression and performance remained unaltered in the control group. The present data suggest that both short- and long-term exercise performances can be improved with a reduction in training volume if speed endurance training is performed and that the Na(+)-K(+) pump plays a role in the control of K(+) homeostasis and in the development of fatigue during repeated high-intensity exercise.

Effect of intensified training on muscle ion kinetics, fatigue development, and repeated short-term performance in endurance-trained cyclists

“…This finding is in agreement with some (3,14) but not all (18) studies in trained runners implementing 10 -30 s near-maximal intervals for 4 -9 wk. Also, no change in H ϩ release during intense exercise was observed in the present study.…”

“…In contrast, other studies implementing intense intermittent training have observed elevated levels of the Na ϩ -K ϩ pump subunits (3,18,34). In the study by Nielsen et al (34) untrained subjects had a higher content of the Na ϩ -K ϩ pump subunits ␣ 1 , ␣ 2 , and ␤ 1 after 8 wk of intense one-legged knee-extensor exercise, and the Na ϩ -K ϩ pump ␣ 1 and ␣ 2 subunits have also been shown to be upregulated in trained runners after 4 -9 wk of intensified and reduced training (3,18). The difference between these studies and the present study may be related to exercise modalities.…”

“…In trained subjects intense training would not be expected to change blood flow (24,46), thus any alteration in lactate and H ϩ release may be mediated by changes in transport proteins involved in lactate and H ϩ transport. Changes in MCT1 and NHE1 content in response to intensified training have been reported in some (6,15,18) but not all (3,44) studies in trained runners and soccer players. Thus it is unclear whether intensified training in combination with a reduced training volume induces changes in muscle ion transport proteins involved in lactate and H ϩ transport in trained athletes, and whether these changes leads to alterations in lactate and H ϩ release during intense exercise.…”

Sex differences and training adaptations in relation to the lactate threshold and endurance exercise performance

“…One of the first studies highlighting the beneficial effects of HIIT in already well-trained athletes (discussed above; [108] ) showed improvements in endurance performance and lactate responses without concomitant improvements in ventilatory measures including V O2max and VT. Since then, research has shown HIIT-related improvements in running performance over 3 km (3%; p < 0.05; HIIT: 6 intervals at 100% V O2max for a duration equivalent to 60% of the time for which the velocity at V O2max can be sustained, for 8 sessions), 10 km (3.1%; p < 0.01; HIIT: 6-12 x 30 sec sprint runs, 3-4 times per week for 6-9 weeks) [28] and the maximum running distance in 20 min (3.8%; p < 0.01; HIIT: ~10 h per week of 40 sec-7 min intervals at 80-90% V O2max for 5 months) [41] without significant improvements in V O2max. Despite one study showing a correlation between the change in V O2max and the change in 3 km performance (r = 0.78; p < 0.05; HIIT: ), the authors concluded that the more likely mechanism behind the performance improvement was the improvement in VT from pre-to post-training (6.8%; p < 0.05) despite the fact that changes in VT were not correlated with changes in performance (r = 0.32) [29] .…”

“…In endurance-trained athletes, small improvements in performance are critical to success; therefore, establishing the sensitivity of laboratory-derived variables such as peak power output and LT2 to detect these performance changes is important. High-intensity interval training (HIIT), defined as repeated short-to-long bouts of rather high-intensity (80-100% peak heart rate [26] ) exercise interspersed with recovery periods [27] , has been shown to improve running (3-10 km) [28][29][30] , treadmill roller skiing (12 km) [31] and cycling (15-40 km) [32][33][34][35][36][37][38][39][40] time trial performances in trained athletes, although the majority of these studies involved men only [28,30,[32][33][34][35][36][37][38][39][40] , with only one study combining men and women [31] and another not stating the sex of participants [29] . In response to HIIT, LT2 adaptations in endurance-trained athletes have only been reported in response to training interventions over one year [40] , five months [41] , and in one short-term study where seven HIIT sessions were completed in seven days [39] .…”