Cardiovascular training alone will not help you to gain muscle. More specifically, low-intensity cardio doesn’t stimulate the muscles enough to induce a growth response. In fact, if you are a beginner looking to build muscle, it’s recommended that you focus on progressive resistance training first, before incorporating additional cardio.
For more regular gym-goers who are looking to build muscle, whilst staying fit and healthy, we would recommend adding light cardio, either after resistance training sessions or on different days. This will ensure they get the health and fitness benefits of cardio training, without interfering with strength gains and optimal recovery (crucial for muscle growth).
While you can achieve some muscle gain by combining both strength and cardiovascular training (known as concurrent training), cardio alone will not yield the results you are looking for. Muscles need to reach a certain stimulatory threshold to grow, which is why strength training is much better suited. Traditional cardio (low intensity, endurance training) won’t provide an adequate stimulus and may even be counterproductive to muscle growth.