The average resting
heart rate for an adult is between 60 and 100 beats
per minute, while well-conditioned athletes can achieve between 40 and 60 beats per minute. The maximum pulse rate is 220 minus your age, and the target for a healthy pulse rate during, or just after, exercise, is 60-80 per cent of this.
Therefore, if you are aged 50, you should aim to build up fitness gradually until you reach a target pulse rate during exercise of between 102-136 bpm (beats per minute).