If you can't take your heart rate a good way to recognize that you're exercising efficiently is whether or not?

you can maintain a conversation while exercising. If you can talk comfortably, you're likely in a moderate-intensity zone; if you struggle to speak, you're probably working at a higher intensity. Additionally, paying attention to your perceived exertion can help gauge your workout's effectiveness. Feeling challenged but not overly fatigued is a good sign of efficient exercise.