Strava Relative Effort: Is It Still Accurate in 2025? (Bugs & Fixes)

Strava introduced Relative Effort (RE) in April 2018 as a direct replacement for its old and much-loved Suffer Score. Since then, it has become one of the core training-load tools for millions of athletes, with occasional tweaks, including a known 2025 bug that affected some users’ Max HR zones.

Relative Effort encompasses strava’s related features like Fitness & Freshness, and Weekly Relative Effort tracking, which are subscriber-only features (UK approx £60-£80pa).

What is Relative Effort & How Does It Actually Work?

Developed in collaboration with Marco Altini, PhD and owner of  HRV4Training, Relative Effort (RE) is Strava’s proprietary metric that quantifies the total cardiovascular (internal) training load an athlete experiences during a workout. It relies heavily on the widely used Bannister’s TRIMP (Training Impulse) model, but tuned to prioritise intensity over duration – meaning a 20-minute interval session can produce a similar RE to a 3-hour easy ride.

The algorithm weights time spent in each heart-rate zone with progressively higher coefficients, thus time-in-Zone 5 contributes far more than time-in-Zone 2. The final score is then normalised using Strava’s global dataset so that efforts are comparable across sports (running, cycling, swimming, rowing) and between users.

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Why did Relative Effort Replace Suffer Score?

The old Suffer Score had two major flaws:

1. Sport bias – runners scored dramatically higher than cyclists for equivalent efforts
2. Duration bias – long, easy sessions were scored higher than shorter, maximal ones

RE removes both by using cross-sport weighting factors.

Source: Strava Engineering Blog (2018), Strava Support.

Key Limitations & Accuracy Issues (2025)

Broadly speaking, RE is a solid approach to load quantification. It has a few minor and occasional inconsistencies, but its most significant issue is the accuracy of the data which it uses.

• Max HR & zone accuracy is everything – wrong Max HR = wrong RE and Fitness/Freshness charts. Age-based HRmax estimates, such as the 220-Age formula, can be off by 10–20 bpm. Some competitor alternatives allow more precise zones calculated via threshold heart rate (LT2, LTHR, AnT), but Strava does not support LTHR. However, you can and should manually set HRmax if you know it. If you don’t know it, check your hardest sustained workouts for the maximum HR you achieve.
• Your source of heart rate – Optical HR is inherently inaccurate. A beat or two deviation from the actual value will make little difference to the RE calculation, but peaks and troughs of 10bpm will make a difference and can be common (use a chest strap).
• Heart-rate confounders: heat, dehydration, caffeine, illness, and stress all increase heart rate, and hence RE, without producing extra mechanical work.
• Underestimates ultra-endurance low-intensity load.

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Known 2025 bug: Strava sometimes auto-recalculates Max HR and shifts zones – fix by toggling sport type in settings (Strava Community thread).

Relative Effort vs Training Stress Score (TSS / rTSS)

You may also hear the phrase “Training Stress Score” (TSS) used to mean the same thing. It’s a different way of measuring internal load, typically favoured by cyclists using a bike power meter. TSS is probably a slightly superior metric, but it has its own drawbacks.

	Relative Effort (Strava)	TSS / rTSS (TrainingPeaks)
Type	Internal load (cardiovascular strain)	External load (actual work done)
Data source	Heart rate	Power meter or pace vs threshold
Confounders	Heat, caffeine, illness	Very few
Best for	Multi-sport athletes without power	High-performance periodisation

Advanced trick: compare RE vs TSS from the same workout. If the RE rise is disproportionately higher, it indicates increased inefficiency as you fatigue (TrainingPeaks TSS explainer).

Relative Effort vs Garmin Exercise Load

Garmin’s equivalent metric is called Exercise Load, and is more similar to RE than it is to TSS. Garmin’s metric is based on estimated EPOC, which is the amount of additional oxygen your body uses after finishing the workout. It is used in a similar way to assess cumulative load and the athlete’s Training Status.

Weekly Relative Effort & Load Management

The coloured bar showing the current week in context to the recent past uses a 3-week rolling average as a proxy for Acute: Chronic Workload Ratio. (Acute means short-term, chronic is longer-term)

RE is displayed using a graph with a typical white “range” band (based on a 3-week average) and colours for weekly trends:

• Green (in range) – sustainable progressive training
• Orange/Red (above range) – you must follow with recovery to achieve the adaptation from this type of training
• Blue (below range) – recovery or taper phase, perfect before a race.

 

On Your Watch (Garmin, Wahoo, Apple, Suunto)

Your live RE performance is available on Garmin devices via the Connect IQ app store, and some competitor watches.

• Garmin: Strava Relative Effort CIQ app (over a million downloads)
• Wahoo: a built-in, native metric
• Suunto: from the SuuntoPlus store