There is no doubt that exercise is one of the key factors for weight loss along with proper diet. Exercise is broadly divided into two types – aerobic exercise (cardio)and anaerobic exercise (weight training).
Aerobic exercise involves exercises which boost the heart rate and blood circulation by repetitive movements of the limbs such as running, cycling, skipping, dance, etc. These exercises recruit limited number of muscle fibres and the oxygen demand is generally fulfilled during the work out so that there is less of lactic acid accumulation in the muscle tissue. Aerobic exercises make use of stored glycogen in the liver and muscle in early phase and begin to burn fat only in the later phase of exercise when these stores are exhausted, i.e. after 15-20 minutes of moderate intensity workout. Thus , fat burning occurs only if aerobic exercise is continued for longer duration of time.
On the other hand, anaerobic exercise or weight training involves exercise which recruit large number of muscle fibres of a single or multiple muscle group at any given time. This leads to increased oxygen demand which cannot be fulfilled immediately and early lactic acid accumulation. Also, there is muscle fibre breakdown when lifting heavier weights which stimulates muscle growth and hypertrophy in the long term. Increased body muscle mass leads to increased resting BMR which in turn burns more calories at rest. Thus, weight training not only burns more calories in a shorter span of time but also leads to increased BMR in the long term which promotes weight loss.
To conclude, both cardio and weight training exercises contribute to weight loss however, weight training can have a greater long term impact by increasing the lean body mass and BMR of the body.