Last week I was reading a book on strength training for women when I came across support for spot reduction or the training of a specific body part to reduce fat in that area. This workout myth has long been discredited by science, but still pervades our thinking because we want it to be true. However, we cannot control from where we burn fat during workouts.
Fat loss is not localized. Having a toned physique requires building muscle through resistance training and shedding the fat covering those muscles. Fat is primarily stored as triglycerides in fat storage cells which are located throughout the body. To use fat for energy during workouts--typically low to moderate intensity workouts--fatty acids are released into the bloodstream and carried to the working muscles. But contracting specific muscles does not generate fat loss in the tissue surrounding those muscles. This fact was demonstrated in a 2013 study that measured the effect of the single leg-press exercise on body fat. The subjects performed between 960-1,200 reps of the leg press exercise on one leg, 3 times per week, for 12 weeks. At the end of the study, the researchers observed a loss of 1.5 pounds of whole-body fat in the subjects. But the fat loss occurred to a greater extent in the subjects' arms and torsos and not, as you might have expected, in their legs.
Exercises employed for "trouble areas" do not burn fat. Workouts built on the concept of spot reduction typically focus on smaller muscles through exercises that mobilize only one joint at a time (e.g., triceps kickbacks, crunches, inner thigh adduction). These exercises are low in intensity, require less energy to complete and therefore burn less fat than higher intensity workouts. Furthermore, these muscles can be trained through multi-joint exercises such as push-ups (triceps) and sumo squats (inner thighs) that are more effective for fat loss.
How to obtain a more toned physique. To efficiently achieve a more toned appearance, you need to simultaneously build muscle and lose fat. This requires a combination of cardiovascular and resistance training. If you have limited days to workout, you can combine the two by performing multi-joint exercises as supersets or in a circuit to minimize rest and increase intensity. If you still want to include single-joint movements (some days I feel that way too), then add them to the end of the workout when you can fatigue these muscles without jeopardizing the rest of your workout. Proper nutrition is also a key component for fat loss because, as we've already seen, you can't burn off a bad diet.