The body quickly becomes accustomed to the resistance placed upon it and will only develop enough muscle mass to deal with such external loads. The principle of overload teaches that for any training adaptation to take place (growth and strength), then the body must work against a load greater than it is used to. For muscular endurance, the muscles must work for a greater period of time than what they are used to.
I see so many people always performing 3 sets of 10 or 12 reps, because they think that the only way to grow is to stay within the recommended hypertrophy rep range (6-12 reps). There is always more than one way to skin a cat; variety in training and time under tension is key. I will discuss training methods in more detail next time but you could try not counting reps at all and simply doing as many reps as you can until your muscles fail on every set....You may surprise yourself and be able to actually do 15- 20 reps of your "usual" weight. This doesn't mean that you won't grow because it's outside of the hypertrophy rep range, in fact, you are more likely to grow due to greater time under tension and putting your body under more stress than it is used to.
If you overload your body in a way that it doesn't see coming, then this will create damage to the muscle tissue causing micro tears to the fibres. This is what is required in order for the muscle tissue to repair and grow bigger and stronger.
So....If you feel those reps getting too easy
then don't cheat yourself, increase the weight, increase the reps, increase the
time under tension or be prepared to plateau.
Now this is the bit that will probably scare some people, women in particular...in order to generate new muscle and grow, our bodies require a calorie surplus. This means you need to eat more calories than you burn during the course of the day including your workouts. This doesn't have to be a massive amount of additional calories, as little as 100 extra calories (the equivalent of a medium sized banana) may be sufficient, depending on an individual’s specific goals. Without the additional calories, you may get stronger but there will be nothing left over for muscle growth.
These calories should come from anywhere between 5-8 meals a day and consist of all three macronutrients (carbs, fats and protein). Unless you want to have a lot of fat to shift when you come to shredding, then I suggest keeping the foods you are eating to gain mass, as clean as possible. Some good examples are - sweet potato, rice, oats, eggs, nuts, avocado, chicken, steak, salmon, etc. In addition, I would recommend that post workout, a meal high in simple carbs is eaten because this is imperative to enable the body to start the recovery process, as following an intense workout the body is depleted of glucose (available energy) and glycogen (stored energy). This is also a time when you're inulin sensitivity will be at its peak, ensuring that the sugars consumed alongside your protein shake, are pushed into the muscles for growth and to refuel them.
Failing to provide your body with sufficient nutrition will result in your body entering a catabolic state and muscle being broken down for energy; the last thing anyone who takes their training seriously would want to happen. This is also why eating a slow releasing, high protein meal (cottage cheese, casein, turkey, etc.) before bed is a must.
Last, but by no means least, is recovery. This is probably the most overlooked component when it comes to bodybuilding. You can have your diet and training spot on but if you don't rest and allow your body a chance to recover then you can't expect to achieve maximum growth.
When we train so frequently and so intensely, we are essentially "breaking down" our muscles. Our bodies need the right nutrition and recovery period in order to repair and grow bigger and stronger before they are broken down again.
Aim for 8 hours sleep a night (although this is easier said than done, especially if you have young children) and set aside at least one rest day a week where you allow your body the opportunity to heal and it will thank you for it.