REF-869 · Bangsbo et al., 2009 · Journal of Applied Physiology, Vol. · Paper · PubMed

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

Blimited evidenceMeasured on trained to highly trained athletesWritten before October 2026, being re-checked

Seventeen endurance-trained runners either replaced part of their training with speed endurance training (six to twelve 30-s sprint runs, 3-4 times a week) while cutting total training by 25%, or continued their usual endurance training (about 55 km a week), for 6-9 weeks.

The speed endurance group raised muscle Na+-K+ pump α2-subunit expression by 68%, lowered plasma potassium during repeated intense running, and improved a 30-s sprint, a supramaximal exhaustive run, 3-km time and 10-km time, with VO2max unchanged. The control group did not change.

Participants

n=17 endurance-trained runners (abstract: "17 runners"): speed endurance training group (SET) n = 12; control group n = 5. Sex and age are not given in the abstract.

Protocol

SET: 6- to 9-wk period with a 25% reduction in the amount of training, including speed endurance training of six to twelve 30-s sprint runs, 3-4 times/wk.
Control: continued endurance training (approximately 55 km/wk).
Outcomes: muscle Na+-K+ pump α2-subunit expression, plasma K+ during repeated intense running, 30-s sprint test, supramaximal exhaustive runs, maximal O2 uptake, 3-km and 10-km times.

Key Results

Na+-K+ pump α2-subunit: 68% higher after 9 wk in SET (P < 0.05); plasma K+ reduced during repeated intense running (P < 0.05).
30-s sprint test: improved by 7% (P < 0.05); first supramaximal exhaustive run: improved by 36% (P < 0.05).
Maximal O2 uptake: unaltered in SET.
3-km time: reduced from 10.4 ± 0.1 to 10.1 ± 0.1 min (P < 0.05); 10-km time: improved from 37.3 ± 0.4 to 36.3 ± 0.4 min (means ± SE).
Control: muscle protein expression and performance unaltered.

Practical Application

In endurance-trained runners (12 training, 5 controls), cutting total training by 25% while adding six to twelve 30-s sprint runs 3-4 times a week for 6-9 weeks improved 3-km time (10.4 to 10.1 min) and 10-km time (37.3 to 36.3 min) with VO2max unchanged, alongside a 68% rise in the muscle Na+-K+ pump α2-subunit. To "can I run less and still get faster?": in this trial, yes — if the volume that was cut is replaced by short, near-maximal speed endurance work.
The gains came without a change in VO2max, so the benefit sits in tolerance of intense running and fatigue control, not in a bigger aerobic ceiling.
Inference, not tested here: this is a tool for a block or a busy period, not a reason to abandon the aerobic volume that the rest of the base supports; the trial lasted 6-9 weeks.
Not from this paper; the base's own practice: where speed endurance sits in the week and season is in SYNTH-46; its place in middle-distance and 5-10 km preparation in SYNTH-60 and SYNTH-47.

Limitations

n=17 with a control group of five; allocation method not stated in the abstract.
The intervention lasted 6 to 9 weeks (varying between runners); longer-term effects are unknown.
Performance results are means ± SE; the abstract gives no statistics for the 10-km change.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

parallel controlled trial, n=17, control group of five