WHOOP’s July heart rate update, tested on the biceps

WHOOP’s heart rate got more accurate on 6 July 2026, and by coincidence I ran two biceps tests since then that verified some potential improvements.

WHOOP names weightlifting, functional fitness, HIIT, cycling and golf as the activities with the biggest gains, implying gains elsewhere as well, and then warns that Strain figures may shift slightly because Strain is calculated from heart rate. The update applies automatically, with no setting to find or toggle.

Two tests, worn on the biceps

Two accuracy tests run on this site in the past week, both with WHOOP MG on the biceps, produced some of the tightest agreement figures recorded here this year. Neither was designed to test the update; the heart rate improvement only became a plausible explanation afterwards.

On 30 July 2026, an open water swim test paired WHOOP MG (left biceps) against Polar Sense (right biceps), Apple Watch Ultra 3 (left wrist) and a wrist-worn Garmin CIRQA. WHOOP averaged 119.42 bpm, Polar Sense 121.89 bpm and Apple Watch Ultra 3 113.87 bpm, all three showing excellent bias and tight limits of agreement. CIRQA, on the wrist, averaged just 99.45 bpm and 96.77 bpm across its two split files, a 20 to 30 bpm under-read against the other devices.

On 31 July 2026, a five-rep interval running session on the Thames towpath paired WHOOP against Fitbit Air, Apple Watch Ultra 3, a Frontier X Plus chest strap and Garmin CIRQA. WHOOP and Fitbit Air produced the strongest pairing of the session: bias +1.0 bpm, limits of agreement -2.3 to +4.3 bpm across 846 matched samples. WHOOP against the Frontier X chest strap matched that +1.0 bpm bias, with wider limits of agreement of -5.7 to +7.8 bpm on just 92 matched samples. Garmin CIRQA read low again, biased roughly 9 to 10 bpm against the other four devices with the widest limits of agreement in the group.

Neither test was on WHOOP’s named activities

WHOOP names weightlifting, functional fitness, HIIT, cycling and golf for the biggest gains from the July update. Running and open water swimming aren’t on that list. WHOOP’s wording covers accuracy improvements across activities generally, with those five singled out for the largest gains, which leaves room for smaller, unlisted improvements elsewhere. Biceps placement produces strong WHOOP results regardless of firmware, so neither test isolates the update as the cause.

Against that background, both figures sit at the tight end of what WHOOP MG has produced on the biceps here this year rather than marking a step change: a June interval test, run before the update, put WHOOP against Polar SENSE at bias +0.3 bpm with limits of agreement of -2.2 to +2.8 bpm. The post-update numbers are comparable, fractionally different depending on which device sits opposite WHOOP.

Take out

WHOOP doesn’t name running or open water swimming among the activities with the biggest July gains, though its wording doesn’t rule out improvement there either. Two biceps tests, one in water and one on land, both landed among the tightest agreement figures WHOOP MG has produced on this site this year.

Quick answers

How accurate is WHOOP MG heart rate on the biceps after the July 2026 update?
In testing since WHOOP’s 6 July 2026 heart rate algorithm update, WHOOP MG worn on the biceps agreed closely with other reference devices. Against Fitbit Air across 846 matched running-interval samples, bias measured +1.0 bpm with limits of agreement of -2.3 to +4.3 bpm.

What did WHOOP change in its July 2026 heart rate update?
On 6 July 2026, WHOOP shipped a new heart rate algorithm improving accuracy in activities it names as historically hardest to measure: weightlifting, functional fitness, HIIT, cycling and golf. Strain values may shift slightly because Strain is calculated from heart rate.

Is WHOOP MG accurate for open water swimming?
In an open water swim test on 30 July 2026, WHOOP MG worn on the biceps averaged 119.42 bpm, closely matching Polar Sense (121.89 bpm) and Apple Watch Ultra 3 (113.87 bpm), all three rated with excellent bias and tight limits of agreement.

Other WHOOP updates this month

July also brought a trend-chart feature in WHOOP AI, voice and text logging in the Journal, and a heart rate graph for fine-tuning activity start and end times on iOS.

Last Updated on 31 July 2026 by the5krunner

the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID