REF-1735 · Qing et al., 2026 · PeerJ, · Paper · PubMed · Free full text

A 6-min priming bout at high intensity, at low intensity, or at low intensity with thigh blood-flow restriction, each followed by 6 min of easy pedalling, left VO2 kinetics, muscle oxygenation and blood lactate in a following 10-min hard cycling bout no different (only baseline VO2 was higher after the high-intensity prime) in 16 national-level sprinters; a randomised crossover with markers only, no performance measure and no no-priming control, read in full

Main caveat: No performance outcome; every comparison is of markers, so the level takes the marker step.
limited evidenceMeasured on trained to highly trained athletesRead in full

Qing and colleagues compared three ways of priming before hard cycling in trained sprinters: a high-intensity bout (HIPE), a low-intensity bout at 90% of the first ventilatory threshold (LIPE), and the same low-intensity bout with thigh cuffs inflated to 70% of arterial occlusion pressure (LIPE-BFR).

Sixteen certified national-level 100-200 m sprinters did all three in random order, each as 4 min at 20 W, a 6-min prime, 6 min at 20 W and then a 10-min bout at a fixed load meant to be severe.

During the prime itself the high-intensity bout produced the larger VO2 amplitude, shorter time delay, deeper muscle deoxygenation and larger oxygen uptake, oxygen deficit and blood lactate; cuffs deepened deoxygenation compared with the plain low-intensity bout but did not raise oxygen uptake, deficit or lactate.

In the following 10-min bout, none of VO2 kinetics (primary and slow components), muscle oxygenation, accumulated oxygen uptake, oxygen deficit (p = 0.057) or lactate differed between conditions; only baseline VO2 before the bout was higher after the high-intensity prime.

The authors conclude that the three primes differ acutely but leave similar residual effects, and suggest the 6-min recovery and the mild cuff stimulus as reasons.

Participants

n = 16 (8 M / 8 F), sprinters (100-200 m) holding China's National First-Class certification; age 20.3 ± 1.0 years; 63.5 ± 8.9 kg; body fat 13.2 ± 4.3%; training experience 4.4 ± 1.5 years.
Cycling incremental test: VO2max 45.2 ± 4.9 mL/kg/min; power at VO2max 238 ± 43 W; VT1 99 ± 27 W; VT2 172 ± 32 W.
Women not using hormonal contraception, regular cycles; cycle phase at testing not reported. No sex subgroup analysis.

Protocol

Preliminary: incremental cycle test (50 W warm-up, +30 W per minute) for VO2max, VT1 and VT2; five 10-min constant loads at 35-90% of VO2max for the power-VO2 regression used to compute oxygen deficit.
Primes (6 min each, random order): LIPE at 90% of VT1; HIPE at 0.4 × (power at VO2max − VT1) + VT1, which the authors call approximately 110% of critical power (critical power was not measured); LIPE-BFR = LIPE with pneumatic thigh cuffs at 70% of resting arterial occlusion pressure from 30 s before to the end of the bout.
Sequence per session: 4 min at 20 W, 6-min prime, 6 min recovery at 20 W, then 10 min at the same load as HIPE. Self-selected cadence of 60-90 rpm kept identical across sessions; 18-21 °C; no caffeine for 8 h, no food for 2 h before.
Measures: breath-by-breath VO2 (mono-exponential fit for the prime, bi-exponential for the 10-min bout); vastus lateralis SmO2 by a Moxy monitor (adipose thickness not measured); capillary lactate before, 3 and 5 min after the prime and at 1, 4 and 7 min of the bout; accumulated oxygen uptake and oxygen deficit.
Funding and interests: Fundamental Research Funds for the Centrally-administered Universities (2024TZJK010), funder without a role; no competing interests declared.

Key Results

During the 6-min prime (mean ± SD; units for kinetic and accumulated values not stated in the table):

MeasureHIPELIPELIPE-BFRp
VO2 amplitude25.10 ± 2.7612.91 ± 3.5913.73 ± 3.42< 0.001
Time delay4.01 ± 3.659.80 ± 4.348.98 ± 4.430.001
Time constant (tau)68.59 ± 11.0845.68 ± 12.2251.43 ± 13.53< 0.001
SmO2 minimum, %48.69 ± 5.3456.26 ± 3.9352.52 ± 5.650.001
Accumulated O2 uptake12,265 ± 1,8578,604 ± 1,7308,706 ± 1,782< 0.001
Accumulated O2 deficit1,989 ± 6791,081 ± 540958 ± 568< 0.001
Accumulated blood lactate, mmol/L5.08 ± 2.213.13 ± 1.402.69 ± 2.000.002

During the following 10-min bout:

Measureafter HIPEafter LIPEafter LIPE-BFRp
Primary amplitude (A1)19.03 ± 3.1618.66 ± 3.2018.94 ± 2.910.940
Primary tau31.99 ± 8.0134.54 ± 6.8431.47 ± 9.320.526
Slow-component amplitude (A2)7.60 ± 3.179.44 ± 2.759.10 ± 3.210.207
Baseline VO215.65 ± 1.8213.48 ± 1.4513.58 ± 1.51< 0.001
SmO2 minimum, %47.58 ± 6.7049.23 ± 5.9146.03 ± 7.880.447
Accumulated O2 deficit1,306 ± 6361,925 ± 8191,868 ± 8690.057
Accumulated blood lactate, mmol/L7.41 ± 3.187.69 ± 1.987.09 ± 2.600.81
In the prime, the abstract says the low-intensity conditions gave a longer time delay; Table 2 also shows a shorter tau with low intensity, which the abstract does not mention.
Correlations (difference scores, HIPE vs LIPE): accumulated O2 uptake with amplitude r = 0.71, time delay r = −0.66, tau r = −0.59; HIPE vs LIPE-BFR: SmO2 minimum with lactate r = −0.66, SmO2 steady state r = −0.60.

Practical Application

Which of three 6-min primes came before a 10-min hard ride did not significantly change the oxygen-uptake response, muscle oxygenation or lactate in that ride when 6 easy minutes separated them (16 sprinters, markers only; performance not measured and no no-prime condition). It does not test whether priming helps; it says a hard prime did not beat a light one on these markers in this set-up.
Thigh cuffs on a light prime deepened muscle deoxygenation but did not raise whole-body oxygen uptake, oxygen deficit or lactate, and changed nothing in the following bout. Inference, not tested here: blood-flow-restriction cuffs add equipment and discomfort to a warm-up without a shown carry-over at this pressure.
The hard prime left baseline VO2 higher at the start of the bout, which the authors read as incomplete recovery after only 6 min; the oxygen deficit in the bout was lower after the hard prime but not significantly (p = 0.057).
SYNTH-66 advises one priming bout below critical power, finished about 10 min before short hard work, and cites a 7-min trial where a moderate or heavy prime raised power (REF-270) and one where severe priming helped only with a fast start (REF-279).This study does not contradict that: it has no performance outcome and no unprimed condition, and its "high-intensity" prime by the authors' formula sat on average below the group's second-threshold power (our arithmetic, below).The guide's VO2max-interval row also cites REF-271, where a 6-min heavy prime 6 min before raised the primary VO2 amplitude and cut the slow component; here the hard prime with the same 6-min gap changed neither against a light prime, but REF-271 compared priming with no prior exercise, which this study did not include.

Limitations

No performance outcome; every comparison is of markers, so the level takes the marker step.
No unprimed control condition, so it compares primes with each other, not priming with none (the authors).
One recovery length (6 min at 20 W); the authors suggest it was too short for any priming benefit to show.
Intensity check (our arithmetic on the group means, not individual data): 0.4 × (238 − 99) + 99 ≈ 155 W, below the group's mean VT2 power of 172 W, so the "approximately 110% of critical power" label for HIPE and for the 10-min bout is not supported at group level; critical power was never measured. Lactate in the bout (7.1-7.7 mmol/L accumulated) does show a hard effort.
Sprinters tested on a cycle ergometer, not in their sport; small, mixed-sex sample without a sex analysis; SmO2 sensitive to adipose thickness, which was not measured; mild outliers were winsorised.
The participants are called "National First-Class" in the methods and "moderately trained" in the discussion; no race times are given.
How this entry was checked and changed
Why this level

a crossover of 16 (the rubric's B+ band for crossovers of 15 or more) taken one step down because every outcome is a marker (VO2 kinetics, near-infrared muscle oxygen saturation, blood lactate, oxygen deficit) and no performance was measured