Listen to your body. If you have a training day scheduled on paper but feel like rubbish, a day off focused on quality nutrition and adequate rest might actually improve your results. After all, you damage muscle in the gym; you build it with quality rest and nutrition. Pushing through when you're overly tired can be a recipe for disaster or injury.
That’s it for Basic Strength and Muscle. Novices and casual exercisers can expect a 20-40 percent increase in strength and some muscle size and muscle endurance enhancement. You could continue with this program beyond the 18 weeks by increasing the weight load as strength and capability improves. However, further progress may depend on alterations in exercise variety, frequency and timing. The next phase should be an intermediate program designed to enhance the progress you’ve already made.
I recommend a cyclical approach to bulking and cutting to optimize anabolic hormones and minimize unwanted fat accumulation. This could be 16 weeks of above-maintenance intake for lean mass gains, followed by 16 weeks below-maintenance intake for fat loss. Of course, feel free to experiment with what works best for you. When done correctly, this approach will yield considerable lean mass gains while you stay pretty darn lean.
When you lose weight, you need to hold onto muscle and bone while shedding fat. This is tricky because the body is not used to breaking down some tissue (fat) and building up other tissue (muscle) at the same time. Breaking down is called catabolism and building up is called anabolism, as in "anabolic steroids." This is a contradictory process. But weight training helps maintain muscle while losing fat.
After session 12, consider whether you need to increase the weight for any particular exercise. If you can comfortably do more than the RM of 12 exercises, increase the weight by a modest amount, say two pounds or a kilogram for isolation exercise muscles such as triceps and biceps, and 5 pounds or 2.5.kilograms for compound and large muscle group exercises like squats and deadlifts. When using dumbbells, this would apply to each one. Don’t increase the number of sets beyond 3 at this time.