The trick to big muscles is not necessarily how much you can press on the bench press but how much blood and growth hormone has entered your muscles which is largely down to how much exercise you do.. Resistance bands are great and easy exercise that can help you gain big muscles but also help with cardio health too! Resistance Bands are great for a full body workout no matter how fit you are you still need to do regular resistance training to maintain mobility and subtlety of your muscles. Resistances training helps also to encourage a habit of good posture and correct natural form which is vitally important to avoid injury!
If you have already injured yourself these bands can be great for helping your body rehabilitate and regain mobility and strength. Injury can weaken muscles and ligaments in your body and make them less resistant to force and much more sustainable to injury as a result. This means gradually rebuilding strength in the injured ligaments and muscles groups is crucially important for a quick and efficient recovery.
By keeping things simple and doing a couple minutes of exercise with resistance bands day by day you can help with your recovery ten fold and instead of jumping straight into exercises which may cause too much stress and over stretching of your weakened muscles and ligaments which could potentially cause damage and hamper your recovers by gradually building up your strength again you run a much lower risk of reoccurring injuries and finding yourself back where you started!
Resistance bands also help cardio health! By using resistance bands of a lower resistance but increasing the rep count you can give your heart a full workout helping to improve the health and efficiency of your heart (TIP you can measure your success by recording your resting heart rate before exercise and after and then doing so again and comparing the results after a couple weeks doing resistances band training).