REF-1501 · Carnes & Mahoney, 2019 · International Journal of Sports Physiology and Performance · Paper · PubMed

Can 3 runs plus 3 CrossFit match 5 runs for a 5 km?

In 21 recreational runners, 12 weeks: no detected 5-km difference (5 runs −6.21%, 3 runs −5.49%, P = .79), not equality; VO2max rose more on 5 runs. Allocation unstated; no mixed race.

Main caveat: Read from the abstract only. Not open access; no allocation method, per-arm numbers, dropouts, baseline fitness, CrossFit content or funding available.
limited, mixed evidenceMeasured on recreational to trained athletes

Twenty-one recreational runners completed 12 weeks of either polarised endurance training (POL) or CrossFit Endurance (CFE), each on 5 training days a week. POL ran on all 5; CFE ran on 3 and did CrossFit on 3, with one day holding both. Intensity zones came from ventilatory thresholds.

POL ran 283 min and 47.3 km a week, CFE 117 min and 19.3 km, and CFE spent more of its time hard (39% vs 15% in zone 3). The 5-km time trial improved by 93.8 s in POL and 84.2 s in CFE with no difference between groups (P = .79); body fat fell similarly (P = .88). VO2max rose in both, more in POL (P = .04, d = 0.85).

Our reading: for a 5 km in recreational runners, a much lower running dose with hard mixed sessions showed no detected deficit, with less VO2max gain; "no difference" here is about 10 people an arm, not proof the plans are equal. Allocation is not stated in the abstract.

Protocol

Who: n = 21 recreational runners; split per arm, sex, age and baseline fitness are not in the abstract.
Length: 12 weeks, 5 training days a week in both arms.
POL: ran 5 days a week. Prescribed 295 (67) min a week at 85%/5%/10% in zones 1/2/3.
CFE: ran 3 days a week and did CrossFit 3 days a week (run + CrossFit on 1 day). Prescribed a lower volume, 110 (18) min a week, at 48%/8%/44%. The length and content of the CrossFit sessions are not in the abstract.
Zones: low, moderate, high by ventilatory thresholds.
Outcomes: 5-km time trial, VO2max, body composition.
Funding and interests: not in the abstract.

Key Results

OutcomePOLCFEBetween groups
Running done283 (75.9) min/week, 47.3 (11.6) km/week117 (32.2) min/week, 19.3 (7.17) km/weekP < .001
Distribution, zones 1/2/374%/11%/15%46%/15%/39%Zone 1 and zone 3 P < .001
5-km time trial−93.8 (40.4) s, −6.21% (2.16%), P < .001−84.2 (65.7) s, −5.49% (3.56%), P = .001P = .79
Body fat−2.45% (2.59%), P = .02−2.62% (2.53%), P = .04P = .88
VO2max+4.3 (3.6) mL/kg/min+1.78 (1.9) mL/kg/minP = .04, d = 0.85; both P ≤ .01 within group

Spread of change: the abstract gives SDs of change, no non-exercising control, so a wider spread in CFE's time trial (65.7 vs 40.4 s) cannot be read as non-responders.

Mechanisms

Measured: no significant between-group difference in 5-km gain (P = .79) on very different running doses; a larger VO2max rise with more running.
Authors' interpretation: recreational runners can reach similar 5-km and body-composition gains by either route, with the VO2max gain favouring POL.
Inference: POL ran about 2.4 times the minutes (283 vs 117, our arithmetic), so its VO2max edge can be more training rather than a better distribution, the point the REF-1213 entry makes about this trial. Why CFE showed no detected 5-km deficit is not shown; its higher share of hard running and the CrossFit work are both candidates.

Practical Application

Can 3 runs plus 3 CrossFit match 5 runs for a 5 km? In 21 recreational runners, 12 weeks: no detected 5-km difference (5 runs −6.21%, 3 runs −5.49%, P = .79), not equality; VO2max rose more on 5 runs. Allocation unstated; no mixed race.
Good for: a gym-origin or time-poor runner who fears that 3 runs a week achieve nothing: for a fresh 5 km in recreational runners, they did not fall clearly behind (B-, abstract).
Not good for: a claim that 3 runs are enough for HYROX, for longer distances, or for well-trained runners. VO2max rose less, and in REF-510 VO2max went with faster HYROX times (correlation, 11 people).
HYROX (transfer): not from this paper; the base's own practice: SYNTH-71's default stays 3-4 runs a week. This trial sits beside the low end of that range; it is not evidence for the default.

Limitations

Read from the abstract only. Not open access; no allocation method, per-arm numbers, dropouts, baseline fitness, CrossFit content or funding available. Whether the groups were comparable at the start cannot be checked here.
Null at about 10 per arm (our estimate from N = 21). The 5-km comparison cannot exclude a meaningful difference either way.
Two things changed at once. Running dose and CrossFit differ together, so the trial cannot say which produced which result.
Different total work is not reported. Running time is given; total training time with CrossFit is not.
Outcome. A 5-km time trial in recreational runners, apparently run fresh, who are likely to improve on almost any structured plan (our inference on both).
How this entry was checked and changed
Why this level

(from the abstract) — n = 21 would sit in the rubric's parallel-RCT 20-39 band only if randomised; randomisation is not stated, so it is a small controlled comparison (rubric B), one step lower as an abstract-only small study with key methods missing: allocation, arm sizes, baseline fitness and CrossFit content. Subscription article, OpenAlex lists no open copy