Training monitoring
Evidence: moderate
The cheapest tools are often the best: a short daily subjective wellness check beats most gadgets. HRV is useful as a 7-day trend, not a single daily reading, and no single metric separates good adaptation from overreaching.
The point of monitoring is to catch maladaptation before it becomes overtraining and to confirm that hard work is being absorbed. The counter-intuitive finding is that the cheapest tools are often the best.
Subjective beats objective
Brief subjective wellness measures, a short daily check of sleep, fatigue, soreness and mood, are more sensitive to changes in training load than most objective markers, and the two generally do not correlate (Saw, Main & Gastin 2016). A short questionnaire outperforms expensive testing for routine monitoring. Session RPE, the rating of perceived exertion multiplied by session duration, is a validated, low-cost measure of internal load that tracks well with heart-rate-based methods (Foster 2001).
Heart-rate variability: useful, but noisy and oversold
HRV-guided training, in which hard sessions are scheduled only when HRV indicates readiness, modestly outperforms fixed plans for VO₂max, but the effect is small, the evidence base is a handful of small trials with very high heterogeneity, and the benefit is larger in amateurs than elites (Granero-Gallegos et al. 2020). HRV should be read as a 7-day rolling average, not as single daily readings, which are too noisy to act on (Plews et al. 2013). Crucially, no single heart-rate or HRV metric can distinguish positive adaptation from overreaching, because vagal HRV and heart-rate recovery rise in both (Bellenger et al. 2016).
This is the same lesson as the wearable-metrics page in a different setting: these numbers are directional trends within one person, not precise readouts, and the branded “readiness” scores built on them carry false precision. Track your own trends, act on large moves, and ignore daily noise.
A simple routine
What monitoring actually looks like
It costs about a minute a day. Score sleep quality, fatigue, soreness and mood on a simple scale each morning. Track load with session-RPE, the perceived effort of a session multiplied by its duration. If you use heart-rate variability, read the 7-day rolling average, not the daily number. Then act on trends and clusters, not single readings: several wellness scores sliding together, or a sustained HRV decline alongside stalling performance, is the cue to insert recovery. One poor night or one low reading is noise, not a signal.
The point is to catch a bad trend a week or two before it becomes overtraining or injury, using cheap subjective measures that, on the evidence above, outperform most of the expensive alternatives.