Fourth Frontier X2 – Adds advanced, Premium fitness, Wellness and Sleep Features

Fourth Frontier X2 Detailed Review

Fourth Frontier X2 is a good and unusual continuous ECG chest strap. It has all the regular features of a high-quality chest strap. Still, it adds several unique features, including recording a detailed and continuous ECG trace as a precursor to conversations you might have with your doctor about heart issues. It also has active alerts to warn you about heart events instantly. These features are specifically targeted at older athletes worried about developing heart issues and those with known or suspected heart issues.

new VO2max – the most accurate measured outside a lab (claim)

The Fourth Frontier X2 now features an ECG-based VO2max estimation determined during exercise, reflecting cardiovascular fitness and overall health. Higher VO2max levels are linked to higher athletic performance, reduced heart disease risks and increased longevity. It is probably the key metric to improve for any human to experience the best possible health span.

The X2’s ECG-driven technology improves accuracy over legacy straps and even the latest optical heart rate monitors on watches, which are susceptible to motion and skin tone variations. Unlike typical fitness trackers, the X2 provides continuous real-time, high-quality ECG data that accurately tracks workout measurements. Combined with Fourth Frontier’s Metabolic Profile Analysis, this accuracy allows users to estimate VO2max outside a lab.

This method also allows Fourth Frontier to determine VT1 and VT2 – ventilatory thresholds, which might be more beneficial to regular athletes than lactate thresholds determined by a one-off lab test. To generalise: those two threshold types will be broadly similar and actionable in the same way.

The algorithms used by Fourth Frontier are here: VO2 Max Validation Study.

new Readiness Score

The Fourth Frontier X2’s readiness score is based on multiple inputs, providing a comprehensive view of daily preparedness.

Heart Rate Variability (HRV) is a primary factor, reflecting stress and recovery through the autonomic nervous system’s control of heartbeat intervals. Other important inputs include sleep quality (especially deep and REM sleep) for recovery and physical and mental stress levels, influencing HRV and resting heart rate. Training Load, based on recent workout intensity and duration, also affects readiness by adding muscle fatigue and cardiovascular strain.

Nutrition and hydration play a further role, as balanced intake supports recovery, while illness or injury can lower readiness as the body prioritises healing. Finally, alcohol and stimulants, like excessive caffeine, can disrupt sleep and impair recovery, further reducing the readiness score. Together, these inputs help users gauge and optimise their daily activity levels.

To use the readiness score on the Fourth Frontier X2, check it daily to see how prepared your body is for physical or mental activity. A high score means you’re ready for intense workouts, while a low score suggests taking it easy with activities like yoga, recovery running, or even walking.

To improve your readiness score, focus on quality sleep, manage stress with relaxation techniques, and balance intense workouts with rest days. Maintaining good nutrition and hydration also supports recovery. By monitoring and adjusting activities based on your readiness score, you can make steady fitness gains while reducing the risk of injury.

new Sleep Stage Analysis

Broadly, DEEP sleep is for physical restoration, and REM sleep is for cognitive restoration.

Fourth Frontier X2’s Sleep Stage analysis gives Premium Subscriber useful insights into the quality of sleep and the time spent in each stage. Understanding these patterns can optimise sleep habits, ultimately enhancing overall well-being and performance. The Frontier X2 uses advanced sensors to continuously track heart rate, movement, and breathing. Unusually, Fourth Frontier X2 stands out by using continuous ECG technology, which theoretically provides superior sleep stage tracking because of the highest level of accuracy in the raw metrics – heart rate and HRV data.

Few, if any, wearables are validated for accurate sleep stage determination against a lab-grade polysomnograph. No reviewers can do this.

Take Out

Some valuable features for premium subscribers.

I like that consumers use the most accurate raw inputs possible for the algorithms. That said, the algorithms have limitations, notably the sleep stage algorithm.