Breathing sensor support and HRV analysis

Indoor cycling apps give you power, heart rate, and cadence. That covers the mechanical side of the effort, but it misses something fundamental: how you breathe. Your respiratory response is one of the earliest and most sensitive indicators of intensity. It changes before heart rate does, and it tells a different story than watts alone.

Ride Cave now supports Bluetooth breathing sensors, bringing live ventilation data into your workouts alongside power and heart rate. We have also added a full post-ride analysis tab for breathing and heart rate variability, giving you a deeper look at how your body responded to the effort.

Breathing sensor support

Ride Cave connects to Bluetooth breathing straps that broadcast respiratory data over BLE. The sensor we have tested with is the Tymewear TYME chest strap, which measures breath rate, minute ventilation, tidal volume, and inhale/exhale timing. To be clear, this is not an official integration or partnership with Tymewear. We reverse-engineered the BLE protocol and built our own client. If Tymewear changes their protocol, things could break. But for now, it works, and the data is genuinely useful.

Any breathing sensor that follows the same BLE characteristic format should work, though we have only validated the Tymewear hardware so far. If you have a different breathing strap and want to try it, let us know how it goes.

New data items

Once a breathing sensor is connected, five new data items become available in the views builder. You can add these to any view layout and they update in real time during your ride.

Breath Rate shows your current respiratory rate in breaths per minute, with the session average displayed below. Minute Ventilation shows the total volume of air you breathe per minute in liters, calculated from breath rate multiplied by tidal volume. Tidal Volume shows the average volume of each inhale, which is useful for distinguishing between shallow rapid breathing and deep slow breathing at the same ventilation rate. I:E Ratio displays your inhale-to-exhale time ratio. A longer exhale is typical during harder efforts and can be a cue for pacing. Finally, the Ventilation Quad packs breath rate, minute ventilation, and 5-second and 60-second rolling ventilation averages into a single compact cell.

All five data items are also available in the formula builder, so you can create custom expressions that combine breathing data with power, heart rate, or any other metric.

Live charts

Two new chart panels join the existing power and heart rate charts. The Breathing Chart shows a scrolling timeline of breath rate and minute ventilation as they change during the workout. It gives you an immediate visual of how your breathing tracks with intensity.

The HRV Tachogram plots individual RR intervals as they arrive from your heart rate monitor. RR intervals are the time in milliseconds between successive heartbeats. This chart does not require a breathing sensor — it works with any HR monitor that reports RR intervals over BLE. The tachogram is useful for spotting premature ventricular contractions (PVCs) and watching how your heart rate variability responds to different effort levels.

Post-ride analysis

After your ride, a new Breathing & HRV tab appears in the ride summary alongside the existing Summary tab. This tab only shows up when the ride contains breathing or HRV data, so it stays out of the way for rides done without a breathing sensor or compatible HR monitor.

The analysis tab starts with summary metrics. On the ventilation side, you get Mean VE and Max VE (minute ventilation averaged and peaked across the ride), plus Avg BR and Peak BR (breath rate averages and maximums). On the HRV side, you get RMSSD (the primary time-domain HRV metric reflecting parasympathetic activity), SDNN (overall heart rate variability), pNN50 (percentage of successive RR differences exceeding 50ms), and PVCs (premature ventricular contractions detected in the recording). Each metric has an info icon that opens a detailed explanation of what it means and what values to expect.

Below the metrics are five charts. The Ventilation Timeline overlays breath rate, minute ventilation, and power on a single time axis so you can see how breathing tracked with intensity across the workout. VE vs Power (V-Slope) is a scatter plot that can help identify your ventilatory threshold — the point where ventilation starts rising disproportionately relative to power. Breathing Efficiency plots the VE-to-power ratio over time, showing whether you maintained efficient breathing or if it deteriorated as fatigue set in.

The HRV Tachogram shows every RR interval across the ride with PVC markers highlighted. The Poincare Plot graphs each RR interval against the next one, creating a scatter pattern that reveals the overall shape of your heart rate variability. During hard exercise, you will typically see a tight cluster since the heart maintains a steady rhythm. At rest or during recovery, the scatter spreads out.

All charts include hover tooltips that show the exact values as you move your cursor across the data.

What this data tells you

Breathing data adds a dimension that power and heart rate alone cannot capture. Ventilatory threshold detection is one of the most practical applications. The V-Slope plot can reveal the inflection point where your breathing starts to outpace your power output, which is a strong marker of the boundary between sustainable and unsustainable effort.

Breathing efficiency trends are also useful over time. If your VE-to-power ratio at a given wattage drops across weeks of training, your respiratory system is adapting to the load. If it trends upward, you may be accumulating fatigue or fighting something off.

HRV during exercise is a less established metric than resting HRV, but the tachogram and Poincare plot still provide useful information. Spotting PVCs is the most immediate benefit. If you see zero PVCs during exercise, that is completely normal and expected. If you see a handful, that is also common and usually benign. But if you see a significant number, it may be worth mentioning to your doctor.

Getting started

To use breathing data, you need a Bluetooth breathing sensor. Connect it from the device panel during a workout, the same way you connect your trainer or heart rate monitor. Once connected, the breathing data items become available in the views builder, and the post-ride Breathing & HRV tab will appear automatically in your ride summary.

For HRV data, you do not need a breathing sensor at all. Any Bluetooth heart rate monitor that reports RR intervals will work. Most chest strap HR monitors support this. Some optical wrist monitors do as well, though chest straps generally provide more reliable RR interval data.

As always, if you have feedback or run into issues, reach out through our feedback form.