Training Stress Balance

Training Stress Balance (TSB) is the difference between chronic training load (CTL) and acute fatigue (ATL) and shows how fresh an athlete is on a day.

Definition

Training Stress Balance (TSB) is the difference between chronic training load (CTL, «fitness») and acute training load (ATL, «fatigue») from the previous day. The concept comes from the TrainingPeaks Performance Management Chart and is built entirely on the Training Stress Score. A positive value indicates freshness, a negative value indicates accumulated fatigue.

TSB(today) = CTL(yesterday) − ATL(yesterday)

The value itself is not a physiological measurement but an arithmetic construct from exponentially weighted TSS averages. It therefore only describes how the load of recent weeks relates to itself.

Why it matters

The goal of almost every training plan is to be at peak readiness on a specific day. TSB gives a single number for that: it shows whether recent fatigue is still masking the fitness you have built, or whether the body has already absorbed it. During the taper before a race it is the central steering value.

The usual reference ranges are rules of thumb, not physical constants. Which range is actually optimal for a given athlete varies considerably and can only be established by observing several cycles.

TSB range	Form / freshness	Fatigue	Risk
above +25	very fresh, but form already declining	none	detraining, «over-rested»
+15 to +25	race form, ideal for peak performance	low	loss of form if held for long
+5 to +15	fresh, good quality sessions possible	low	none
−10 to +5	equilibrium, normal training days	moderate	none
−10 to −30	productive overload, stimuli are being absorbed	high	overreaching without recovery
below −30	heavily fatigued, usually after a race or camp	very high	overtraining, injury, illness

How obseed measures it

obseed calculates TSB daily from the TSS of every recorded session across all sports. CTL is the exponentially weighted average over 42 days, ATL over 7 days; the previous day’s difference yields today’s TSB.

What matters is the quality of the underlying TSS values. A TSS based on an FTP estimated from a 20-minute field test carries its error straight into CTL, ATL and TSB. obseed therefore recommends establishing performance benchmarks through metabolic testing and updating them regularly, so that TSB says something about the body rather than about a computational assumption.

Example

After eight weeks of build, a cyclist has a CTL of 78 TSS/day and an ATL of 95 TSS/day. Her TSB is 78 − 95 = −17: she is in the productive overload range and the stimuli are being absorbed.

Two weeks before the race she cuts volume by around 40 percent while keeping intensity. On race day the chart shows CTL 74 and ATL 52. TSB is 74 − 52 = +22; she has lost four points of CTL but sits in the +15 to +25 range and is recovered enough for a peak performance.

References

Allen, H., Coggan, A.: Training and Racing with a Power Meter. VeloPress.
Banister, E. W. (1975): impulse-response model of training adaptation (TRIMP).