A device includes a breathing sensor that is configured to obtain breathing data of a user during use. The device also includes a cardiac sensor that is configured to obtain heart rate data of the user during use. The device also includes a processor that is communicatively coupled to the breathing sensor and the cardiac sensor. The processor is configured to calculate a biological metric based at least in part on the breathing data and the heart rate data. The processor can estimate a metabolic parameter of the user based on the biological metric. In some embodiments, the device can also include a motion sensor that is communicatively coupled to the processor to obtain acceleration data of the user during use. In such embodiments, the processor is configured to calculate the biological metric based at least in part on the breathing data, the heart rate data, and the acceleration data.
