By and large humans can get stronger using literally any form of resistance (machines, free weights, body weight, tree branches, etc.) and from a pure strength development perspective these various modalities offer us very similar results. However, there are a few major advantages of machines over free weight exercises and they include:
- Machines typically allow the trainee to achieve a higher degree of intensity/overload. An example of this is the comparison between the barbell squat and a leg press movement. The glutes and quadriceps are never fatigued to the point they should/could be during a barbell squat because the low back becomes a weak link. The leg press eliminates low back involvement and allows the glutes and quadriceps to be fatigued further (and the low back can be targeted through separate, specific exercises).
- Machines often include design features that make an exercise more biomechanically safe and efficient. One example is that a machine chest press can include movement arms that converge thus allowing for greater humeral adduction (the pectorals pulling the arms closer together) when compared to a barbell bench press in which converging movement is impossible.
- Some exercises are simply not possible to perform with free-weights. Examples include leg extension and leg curls.
- What about stabilizers? It is often stated that free-weight exercises are more beneficial because they incorporate stabilizer muscles in order to balance the weight. Motor learning research shows us that after a few workouts with free weights the trainee develops an efficient neuromuscular pattern (i.e. learns the skill of the exercise) and thus does not struggle with balance. In addition, in order to develop muscle hypertrophy, power, improved metabolic rate, etc., intense training for significant muscle tissue is of prime importance.
In summary, machines do possess some inherent advantages over free-weights. However, the proper implementation of any form of resistance will yield excellent and comparable results.
