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Training by feel has a long tradition in sport, but modern wearables now offer extensive data to enable more precise training control. The Amazfit Helio Strap bracelet offers another parameter to help athletes plan their training sessions optimally. The so-called BioCharge Energy Score tracks changes in energy levels throughout the day and is intended to provide a data-based decision-making basis for training intensity. The score is calculated from various factors such as sleep duration and quality, heart rate (including resting heart rate), heart rate variability (HRV), stress level and everyday activities such as walking or active work.
Readiness score - widely used value
The Readiness Score uses various metrics, such as Heart rate variability (HRV), Resting heart rate, sleep quantity and quality, and physical activity to assess a person's state of recovery and readiness for physical activity. The values are normalised and offer a scale from 0 to 100, with higher values signalling better recovery and therefore greater readiness.
Amazfit BioCharge Energy - new value
In contrast to the already familiar Readiness Score, which is available on many smartwatches and indicates physical and mental fatigue in the morning, the BioCharge Energy Score is continuously updated. According to Amazfit, this makes it valuable for athletes who complete their training sessions in the afternoon or evening. What many active people intuitively sense is now made visible through concrete data. However, the basic principle remains the same for both indicators: the higher the value, the more intensive the training can be.
Competitor Garmin offers the training readiness value, which also adjusts throughout the day. Fitbit offers the value Daily Readiness and Whoop the parameter Strain. However, none of the manufacturers reveal how the individual parameters such as sleep quality, HRV, stress level or training load are weighted. A comparison and assessment is therefore difficult.
Recovery data for optimal training planning
The BioCharge Energy Score is just one of many parameters provided by modern sports wearables. Amazfit devices now offer a comprehensive range of recovery and training parameters. These include the training evaluation with aerobic and anaerobic load, the estimated time to full recovery after the last training session and the training load based on oxygen consumption after training. Other important key figures are the 7-day fatigue level, which reflects the acute training load, and the 42-day fitness level, which is based on long-term training and indicates the chronic training load. In addition, there is the morning readiness value, which indicates physical and mental fatigue, and the new BioCharge energy value, which is exclusively available for the Helio wristband.
The heart rate variability (HRV) as an indirect indicator of nervous system fatigue, the resting heart rate, which can indicate overtraining, fatigue or an impending infection if it deviates from the personal average, and the maximum oxygen uptake (VO2max) as a measure of aerobic capacity are also particularly informative for recovery management. Last but not least, the quality of sleep, including the deep sleep phases, also plays a decisive role in recovery.
Training adaptation based on recovery data
The art of effective training lies not only in planning, but also in adaptability. Even the best training plan must be regularly adapted to the current condition of the body, as it cannot be stressed indefinitely. The combination of different recovery parameters enables a differentiated view and helps to make well-founded decisions.
A typical scenario: The training plan includes long intervals, for example three repetitions of three kilometres each at a 10-kilometre pace with three-minute jogging breaks. Heart rate variability (HRV) is high, indicating a well-recovered nervous system, and full recovery from the last workout is imminent. However, the Readiness or BioCharge energy index shows a low value, possibly due to poor sleep quality or occupational stress. In this case, it would make sense to switch from long intervals to shorter but equally fast units - for example, ten repetitions over 400 metres with one-minute walking breaks.
Another example: a long run at marathon pace was planned for the weekend. Despite a good night's sleep, which has improved the BioCharge value or Readiness Score, the muscles are still tired from previous training sessions with inclines. In this case, it would make sense to continue with the long run, but at an easier, more comfortable pace.
Technical specifications of the Amazfit Helio Strap
The Amazfit Helio Strap is a wristband that focuses on recording recovery and energy data. It has sensors for measuring heart rate, heart rate variability and other parameters that are relevant for calculating the BioCharge Energy Score. The wristband is part of the Amazfit range, which includes sports watches, smart rings and now also specialised wristbands. All devices are connected to Zepp Health's proprietary health management platform, which provides cloud-based insights and guidance to help users achieve their goals.
Measured values Amazfit Helio Strap:
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- BioCharge Energy Score (real-time energy score throughout the day)
- Heart rate and resting heart rate
- Heart rate variability (HRV)
- Stress level
- Movement and activity data
- Sleep quality and duration
Scientific background
A recent study looked at various recovery parameters of wearables and their relevance. Wearables that provide composite health scores (CHS) such as recovery or stress values are often marketed as objective indicators of physiological condition, stress and regeneration. However, the scientific evidence behind these scores is limited and inconsistent. Studies show that the calculation methods of CHS - especially the integration of physiological data such as heart rate variability (HRV), resting heart rate and activity levels - are not transparent or consistent.
This raises doubts about their scientific validity. Although some wearable metrics such as HRV show moderate correlations with certain physiological or psychological states, others - such as WHOOP's Recovery Score or Garmin's Body Battery - often do not correlate with objective measurements or subjective feelings of stress. The devices cannot replace body awareness, but they can be an aid to recognising overtraining more quickly, for example.
Study on recovery values for wearables
Doherty, Cailbhe, Baldwin, Maximus, Lambe, Rory, Burke, David and Altini, Marco. "Readiness, recovery, and strain: an evaluation of composite health scores in consumer wearables" Translational Exercise Biomedicine, vol. 2, no. 2, 2025, pp. 128-144.
https://doi.org/10.1515/teb-2025-0001
Kristian Bauer
Editor
