Well, yes and mostly no. First, one has to define what is “the gym”. If we are talking commercial fitness center, of course, yes. If we are talking resistance exercise with little or no equipment (e.g., at home), then mostly yes. If we are suggesting that one can gain muscle mass without resistance exercise, then it is a definitive no.
“Greater muscle mass” infers muscle hypertrophy. (Myofibrillar v. sarcoplasmic is a more refined discussion for another time.) The only way to induce muscle hypertrophy is to stimulate the muscle via systematic progressive overload—i.e. resistance training. Now, theoretically, the amount of muscle hypertrophy might be manipulated by gene therapy to alter the effects of myostatin, but the need for a stimulus is still present.
If by “greater muscle mass” we are implying the maintenance of muscle mass as one ages—i.e., avoiding age-related sarcopenia, then, to a small degree, some form of hormonal or drug treatment may have some benefit. Certainly, protein intake plays a role. There remains, however, the principle of reversibility—i.e., “use it or lose it”. We maintain muscle mass by remaining physically active—at a level that requires the amount of muscle mass to be maintained. In other words, no amount of supplementation, hormonal therapy, or miracle treatments is going to grow muscle without overload.
As we age, we do lose some muscle mass as part of the aging process. The degree to which this is certain to occur is debatable. It is likely to be much less than we have convinced ourselves is the case. It is true that growing muscle is more challenging as we age—but, it is not impossible. Do we need a gym? No. We do, however, need a means of progressively overloading the muscles. As such, body weight exercise will only grow muscle to a point (because our body weight should not be increasing at a rate necessary to keep up with the necessary overload). We can make bodyweight exercises more challenging, though merely increasing repetitions and sets will only benefit to a point. Resistance will have to be added at some point. This can be done by managing lever mechanics (Force = Resistance x Lever Arm) or adding external resistance (partner assisted, bands, weighted vests, etc.). Or one can progress to using barbells and/or dumbbells. Ultimately, the best approach to growing muscle is going to be some “gym” equipment. It doesn’t have to be elaborate. It doesn’t even have to be conventional barbells or machines. Greater muscle mass, however, will require some system for progressively overloading the muscle.
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