REF-756 · Lamberts RP, Lambert MI — 2009 · Journal of Strength and Conditioning Research, · Paper · PubMed
Day-to-day variation in exercise heart rate falls as intensity rises: the lowest within-person variation, about 3 bpm, was at the end of a stage reaching 85-90% of HRmax, and HRR was least variable in the first minute after it
Protocol
Thirty-eight subjects (n = 38) did a graded submaximal protocol (HIMS) on four consecutive days after familiarisation, and were grouped by the fraction of predicted HRmax they reached. Within-subject variation in heart rate was measured across intensities of 61-98% of HRmax and through recovery.
Key Findings
Heart-rate variation fell with increasing exercise intensity in every group.
The lowest variation was at the end of the last stage in the 85-90% group (3 ± 1 bpm) and the >95% group (3 ± 2 bpm).
During recovery, variation was lowest in the first minute after the last stage.
The 85-90% group tended to show the lowest variation overall; the authors recommend a protocol that ends at 85-90% of HRmax.
Practical Application
Read a heart-rate change of about 3 bpm or less at the end of a hard submaximal effort as noise, not form. That is the day-to-day variation measured where it is smallest, at stages ending near 85-90% of HRmax; at easy intensities the noise is larger, so a steady-state check in zone 1-2 needs a bigger change before it means anything.
This is a measurement-noise study on a graded protocol — it does NOT set a heart-rate target for the fixed-power fatigue test (Science to Sport's ~110% FTP × 3 min has none; SYNTH-41). An HR target belongs to heart-rate-clamped tests such as the LSCT.
Measure heart-rate recovery over the first 60 s after the hardest stage — that window was the most repeatable.
Limitations
Mixed, not specifically trained population; running-based protocol.
Four consecutive days only — seasonal drift is not captured.