It is possible to gain size and build muscle without using weights, through the use of bodyweight exercises and other types of resistance training. Here are some tips for gaining size and building muscle without weights:
Incorporate a variety of bodyweight exercises: Bodyweight exercises such as push-ups, squats, lunges, and pull-ups can be effective for building muscle and gaining size. Make sure to vary your workouts and include a range of different exercises to challenge your muscles in different ways.
Use variations and progressions: To continue making progress and building muscle, it's important to progressively increase the difficulty of your workouts. You can do this by using variations of bodyweight exercises (such as single-leg squats or plyometric push-ups), or by adding resistance through the use of bands, suspension trainers, or other equipment.
Focus on high-intensity interval training (HIIT): High-intensity interval training (HIIT) is a type of cardio workout that involves short bursts of intense activity followed by periods of rest. HIIT can be effective for building muscle and increasing size, as it promotes the release of growth hormone and helps to build lean muscle mass.
Eat enough protein: Protein is essential for muscle repair and growth, so it's important to consume enough protein to support your training. Aim for at least 0.8 grams of protein per pound of body weight per day, and consider incorporating protein-rich foods such as meat, fish, eggs, and dairy products into your diet.