But in a pandemic that has forced most fitness centers to shut down, I had to settle for a make-believe boxing class while wearing a computer headset and jabbing and punching with a pair of motion-sensing controllers. Normally, this would be the result of a workout at my local gym. By the end of the 20-minute workout, I’d broken a sweat and my smartwatch showed my heart rate thumping at 140 beats a minute. A group of five boxers and I recently threw punches to upbeat music while an instructor egged us on.