REF-1448 · Enoksen et al., 2011 · Journal of Strength and Conditioning Research · Paper · PubMed

Running 50 km with more threshold work, or 70 km with less?

In 19 young well-trained men over 10 weeks: no between-group difference. Threshold speed rose significantly only at 50 km, but the changes were not compared. Small.

Main caveat: Numbers analysed: 26 in the text, 19 in the tables; dropouts unexplained.
limited, mixed evidenceMeasured on trained to highly trained athletes

Enoksen and colleagues (Norwegian School of Sport Sciences) gave young middle-distance runners 10 weeks of either high-intensity low-volume training (HILV, 50 km a week, 3 sessions and 33% of volume at 82-92% of HRmax, 67% at 65-82%) or high-volume low-intensity training (HVLI, 70 km a week, 1 session and 13% of volume at 82-92%, 87% at 65-82%), both 6 sessions a week and "matched for total work and frequency".

The authors take 85-90% of HRmax as the elite individual lactate-threshold zone, hence "around LT". No between-group differences appeared before or after training. Within groups, velocity at VO2max and at the lactate threshold rose notably only in HILV; running economy improved in both; VO2max did not change in either.

The time-to-exhaustion test did not change significantly in either group. The authors conclude that training close to the threshold gave a better effect. Our reading: the between-group result is a null. The within-group claim rests on similar changes falling either side of p = 0.05, in a group that started slower (vLT 14.6 vs 15.3), and no test compared the changes.

What the trial can support is narrower: taking 20 km a week out of the plan and adding two threshold-range sessions did not visibly cost anything over 10 weeks, in young men who were already running more than either plan held.

Protocol

Participants: twenty-six well-trained men per the text (19.9 ± 6.1 y as printed, 69.8 ± 5 kg), running 90 ± 14 km a week; Table 1 gives n = 10 HVLI and n = 9 HILV, with no account of the other seven.
Allocation: matched on the pre-test performance result, then randomly assigned.
Training: 10 weeks, 6 sessions a week; intensity targets from a heart-rate watch with an alarm at ±5 beats. The Introduction gives the zones as % of VO2max; Methods give them as % of HRmax.
Tests: treadmill at 1.7% incline. vLT as the speed at a fixed 3 mmol/L; VO2max; running economy; performance test as distance and time to exhaustion at vVO2max; test-retest ICCs 0.88-0.92.
Analysis: paired t-tests within groups; independent t-tests between groups at pre-test and at post-test. No comparison of change scores and no baseline adjustment.
Funding and interests: none printed in the manuscript.

Key Results

OutcomeHVLI, 70 km (n = 10): change (95% CI)HILV, 50 km (n = 9): change (95% CI)Between groups at post-test, 95% CI
VO2max (mL/kg/min)−1.2 ± 2.8 (−3.2 to 0.8)1.2 ± 2.4 (−0.7 to 3.1)−0.8 to 5.3
vVO2max (km/h)0.5 ± 0.7 (−0.1 to 1.0)0.8 ± 0.8 (0.2 to 1.4)−1.0 to 0.5
vLT (km/h)0.4 ± 0.7 (−0.1 to 0.9)0.7 ± 0.7 (0.1 to 1.2)−1.2 to 0.3
%VO2max at vLT−2.2 ± 3.9 (−5.0 to 0.6)−2.0 ± 2.4 (−3.8 to −0.2)−4.4 to 0.8
Performance distance (m)218 ± 546 (−172 to 609)301 ± 886 (−341 to 944)−879 to 1018
Lactate after the test (mmol/L)0.4 ± 1.4 (−0.6 to 1.4)0.9 ± 1.1 (0.1 to 1.7)−1.2 to 0.5
Running economy: VO2 at 14.5 km/h fell 2.5 ± 3.0 and 1.8 ± 2.1 mL/kg/min in HVLI and HILV, with no between-group difference.
Individual response: the SD of change is as large as or larger than the mean in every row, in both arms, with no control group.
Numbers that do not add up: the abstract gives performance gains of 456 m and 273 m; Table 3 gives 301 m and 218 m. The abstract's "1.38 min" for HILV is 1.0 in Table 3; the Discussion says "54-98 seconds".

Mechanisms

Measured: vLT and vVO2max significant within HILV only; economy improved in both; VO2max unchanged in both; %VO2max at vLT fell in HILV.
Authors' interpretation: specific training close to the threshold improves vLT, through economy and anaerobic capacity rather than VO2max; they call the result a better effect.
Inference: a fixed 3 mmol/L threshold and short time-to-exhaustion test may respond to changes in lactate kinetics and economy; a drop from 90 to 50-70 km may itself act as a partial taper in both arms.

Practical Application

Running 50 km with more threshold work, or 70 km with less? In 19 young well-trained men over 10 weeks: no between-group difference. Threshold speed rose significantly only at 50 km, but the changes were not compared. Small.
A runner short on time: cutting easy kilometres to fit two extra sessions near the threshold was not visibly harmful in this short block. Not from this paper; the base's own practice: on a short week the quality sessions carry the adaptation and easy time is what is left (SYNTH-51, SYNTH-26), while the 5-10 km build still asks for mostly easy running (SYNTH-47).
What it does not show: that threshold-range running beats easier running (no between-group effect), that 50 km suffices over a season, or any result in women or adult recreational runners. It tested no named band such as sweet spot.

Limitations

Numbers analysed: 26 in the text, 19 in the tables; dropouts unexplained.
No test of the difference in change; the headline claim is within-group.
Baseline difference in vLT (15.3 vs 14.6) not adjusted.
Both arms held threshold-range work, and both cut volume below habitual.
Young men only, with an age SD of 6.1 printed against a mean of 19.9.
Inconsistencies in the anchor (%VO2max vs %HRmax) and between the abstract and Table 3.
Performance test to exhaustion at vVO2max, highly variable (SD of change larger than the mean).
Accepted manuscript read; the journal version may differ slightly.
Funding and interests: not printed.
How this entry was checked and changed
Why this level

the rubric's B for a parallel RCT under 20 on the numbers actually analysed, lowered a step for limits beyond design: unexplained loss of 7 from 26, no test of the difference in change, within-group tests drive the conclusion, and the abstract's performance numbers conflict with Table 3; men only

Full text (checked 2026-10-30)
The participants were matched according to their pre-test results, then randomly assigned; a high volume (70 km) low intensity (65-82 % of HR max) training group and a high-intensity (82-92 % of HR max) low volume (50 km) training group (full text)
The HILV-group performed 33 % of the total training volume at 82-92 % of HR max and 67 % was performed at 65-82 % of HR max; the HVLI-group performed 13 % at 82-92 % and 87 % at 65-82 % (full text)
The HILV-group performed 3 intensive workouts per week and the HVLI-group performed one; both groups were running 6 training sessions per week (full text)
Twenty-six young well-trained males; running 90 ± 14 km per week (full text)
Table 1 headers: HVLI-Group (n=10), HILV-Group (n=9); vLT 15.3 ± 0.8 to 15.7 ± 0.7, change 0.4 ± 0.7, 95% CI -0.1 to 0.9; vLT 14.6 ± 1.0 to 15.2 ± 0.8, change 0.7 ± 0.7, 95% CI 0.1 to 1.2 (full text)
No significant differences were found between the two groups on all measures both before and after the intervention period (full text)
Running distance change 218 ± 546 and 301 ± 886 m (Table 3); the HILV-group made 456 m (1.38 min) and the HVLI-group 273 m (54 sec) in progress (abstract) (full text)
The LT was determined as the vLT that corresponded with 3-mmol lactate (full text)