Training Load — CTL, ATL, TSB

FitOps models your training using three metrics derived from daily Training Stress Score (TSS).

The Three Numbers

Metric	Name	Window	What it means
CTL	Chronic Training Load (Fitness)	42-day EWMA	Long-term fitness built up over weeks
ATL	Acute Training Load (Fatigue)	7-day EWMA	Short-term fatigue from recent training
TSB	Training Stress Balance (Form)	CTL − ATL	Readiness: positive = fresh, negative = fatigued

Formulas

Both CTL and ATL use an exponential weighted moving average (EWMA):

CTL_today = CTL_yesterday + α_ctl × (TSS_today − CTL_yesterday)
ATL_today = ATL_yesterday + α_atl × (TSS_today − ATL_yesterday)

α_ctl = 2 / (42 + 1) ≈ 0.0465
α_atl = 2 / (7 + 1)  = 0.25

TSB = CTL − ATL

On rest days, TSS = 0, so both values decay toward zero.

TSS Calculation

TSS is estimated from activity duration and intensity:

• Running: based on average heart rate zone (z1–z5) if HR data is available, otherwise scaled by duration
• Cycling: power-based if watts are recorded; HR-based otherwise

Sport-specific multipliers are applied so that a hard run and a hard ride contribute comparably to load.

Form Labels

FitOps interprets TSB with descriptive labels:

TSB Range	Label
≥ 15	Very fresh — possibly detrained
0 to 15	Fresh — optimal race readiness window
−10 to 0	Productive — slight fatigue, good adaptation zone
−20 to −10	Overreaching — high adaptation, monitor recovery
< −20	Overtraining risk — reduce load

Ramp Rate

FitOps also computes the 7-day CTL ramp rate as a percentage change:

ramp_rate_pct = ((CTL_today − CTL_7_days_ago) / CTL_7_days_ago) × 100

A ramp rate above ~5–7% per week is generally considered a high injury risk for runners.

Command

fitops analytics training-load
fitops analytics training-load --today     # current values only
fitops analytics training-load --days 42 --sport Run

See Output Examples → Analytics for the full JSON response.

← Concepts