REF-075 · Aagaard et al., 2011 · Scandinavian Journal of Medicine & Science in Sports, Vol. · Paper

Resistance training improves 45-min endurance and shifts fiber composition in young top-level cyclists

Blimited evidenceMeasured on elite to world-class athletesWritten before October 2026, being re-checked

Participants

n=14 young elite competitive cyclists

Protocol

16 weeks of concurrent strength + endurance training (SE) vs endurance training only (E). Outcomes: maximal muscle strength (MVC), contractile rate of force development (RFD), muscle fibre morphology and composition, capillarisation, VO2max, cycling economy (CE), short-term (5-min) and long-term (45-min) endurance capacity. The strength program itself (exercises, loads, frequency) is not described in the abstract.

Key Findings

MeasureSE (strength + endurance)E (endurance only)
MVC and RFD+12-20% (P<0.01)no change
VO2maxunchangedunchanged
Cycling economyvalues already at the level E reachedimproved, to reach the values seen in SE
5-min endurance performance+3-4% (P<0.05)+3-4% (P<0.05)
45-min endurance capacity+8% (P<0.05)no change
Type IIA fibre proportionincreased (P<0.05)no change
Type IIX fibre proportiondecreased (P<0.05)no change
Fibre area, capillarisationunchangedunchanged

Mechanism

The IIX → IIA fibre shift (fast glycolytic → fast oxidative) together with gains in MVC and RFD accompanied the 45-min improvement; fibre area and capillarisation did not change, so the effect is not hypertrophy or vascular. Inference, not tested: a shift toward more fatigue-resistant fast fibres is the plausible route to better long-duration power.

Practical Application

In 14 young elite cyclists, 16 weeks of strength training added to endurance training improved 45-min time-trial capacity by 8% while endurance-only riders did not improve it; both groups gained 3-4% on a 5-min test, VO2max did not change in either, MVC and RFD rose 12-20% only with strength, type IIA fibres increased and IIX decreased only with strength, and fibre area and capillarisation were unchanged.Strength training in elite riders pays off in the long effort, through neuromuscular and fibre-type change rather than muscle growth.
Cycling economy improved in the endurance-only group up to the level already seen in the strength group — so economy is not where the strength group's 45-min advantage came from; the abstract ties it to the fibre-type shift and the strength gains.
The strength program's exercises, loads and frequency are not in the abstract; for prescriptions see the base's strength entries (REF-147 Rønnestad 2017, REF-149 Rønnestad & Mujika 2014).

Limitations

n=14 in two groups; randomisation and group sizes not stated in the abstract
Strength program details (exercises, sets, frequency) not in the abstract
Young elite cyclists; transfer to amateurs or masters not tested here
16 weeks; longer-term retention not reported
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A: two-group training study, n=14; randomisation not stated in the abstract

Content correction 2026-09-27
Added the omitted result: cycling economy improved in the endurance-only group to reach the values seen in the strength group; VO2max unchanged in both.
"Heavy squats 2×/week" -> deleted; the abstract does not describe the strength program. "Type: RCT" -> controlled two-group training study (randomisation not stated).
"Enormous effect for long mountainous racing" -> deleted (editorial). Level A -> B (n=14).