Metrics
Body Battery: quantified energy for smarter training
Garmin's body battery scores your energy reserves from 0 to 100. Gneta turns those numbers into training decisions, showing you when to push, when to rest, and why your energy behaves the way it does.
What You See in Gneta
Daily charge & drain patterns
Gneta plots your body battery curve across each 24-hour cycle and overlays it week-over-week. You will see exactly when your battery charges fastest (typically during deep sleep between 11 PM and 2 AM) and what drains it hardest. A 90-minute threshold run might cost 30-40 points, while a stressful meeting can silently burn 15. Understanding your personal charge rate helps you plan recovery days that actually recover.
Body battery vs training load correlation
When weekly training load rises 15-20%, your morning body battery should still recover above 60 if adaptation is on track. If it consistently opens below 50, load is outpacing recovery. Gneta charts this relationship across weeks so you can see the tipping point where more training stops producing gains and starts producing fatigue.
Optimal training window identification
Your body battery peak usually hits between 6-9 AM after a good night. Gneta learns your personal curve and identifies the time window where hard sessions will cost the least relative recovery debt. Athletes who schedule intervals during their peak window report 8-12% lower RPE for the same power output compared to late-afternoon sessions on a drained battery.
AI-powered energy management advice
Ask the coach: "Can I handle a long ride today?" or "Why is my body battery not recovering?" The AI evaluates your current reading, overnight charge rate, recent training load, sleep quality, and stress levels to give specific guidance. If your battery charged only 25 points overnight instead of your usual 45, it will explain why and suggest adjustments.
The Science Behind Body Battery
Body battery is powered by Firstbeat Analytics' physiological model, which processes four continuous data streams: heart rate variability (HRV), stress level, activity intensity, and sleep quality. The algorithm tracks the balance between sympathetic and parasympathetic nervous system activity throughout the day. During sleep and rest, parasympathetic dominance drives the charging phase. Deep sleep stages contribute roughly 2-3x more charge per hour than light sleep. During waking hours, physical activity and psychological stress drive the drain. A 60-minute easy run might cost 15-20 points, while the same duration at threshold intensity can drain 35-45.
For endurance athletes, body battery fills a gap that training load metrics alone cannot cover. TSS and TRIMP quantify the mechanical and cardiovascular cost of training, but they ignore everything else: work stress, travel, poor nutrition, a toddler waking you at 3 AM. Body battery captures the total recovery picture. This is why two athletes with identical training loads can have completely different readiness: one sleeps 8 hours in a dark room, the other manages 6 hours of fragmented sleep. Their body battery curves will reflect this difference long before performance metrics do.
The most actionable pattern to track is your overnight charge rate. In Gneta, this is calculated as the difference between your evening low and morning high, divided by sleep hours. A healthy, well-recovered athlete typically charges at 6-8 points per hour. During a heavy training block, this might drop to 4-5 points per hour, which is expected and manageable. Below 3 points per hour for more than two consecutive nights is a strong signal to reduce training load or address a non-training stressor. Gneta surfaces this metric prominently because it is more reliable than a single morning reading, which can be skewed by when you woke up or how long you stayed in bed.
Frequently asked questions
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