It is well established that a structured resistance exercise program safely, effectively builds muscle & strength in adults of all ages.
That's important. Adults lose muscle every decade of life which appears to underline all the perils of ageing - osteoporosis, type-2 diabetes, cardiovascular disease, unwanted weight gain, an increased susceptibility to illness and fall-related injuries.
Yep, hoisting the iron offers the best protection against all of these. In fact muscle loss-related illnesses cost our healthcare system over 14 billion dollars every year in Australia. 
So the next question I often get asked is, "how heavy do I need to lift to experience all the benefits?"
That's a great question!
Resistance exercise is actually just a signal - a stimulation to build bigger stronger proteins in muscle.
That all-important "signalling mechanism" to build and regenerate occurs via the stimulation of protein synthesis rates within the muscle.
Lifting weights - the old fashioned barbells and dumbbells is still the most scientifically valid method of triggering the highest known rates of muscle protein synthesis.
In the gym intensity (effort) is measured by the load used and this is described as the RM, repetition maximum.
The RM refers to the number of maximum-effort reps that can be performed in a set of a particular exercise. Good weight lifting programs manipulate the RM (load and effort) to speed results from working out.
A series of truly amazing studies have looked at the molecular level, what RM load or intensity is required to maximize muscle protein synthesis.
Kumar et al  were the first to establish that loads of 60-90% of the 1RM are required to activate the molecular processes responsible for activating protein synthesis in muscle.
This is in general agreement with other research groups that have shown increases in muscle mass and strength with resistance training are greater with higher exercise intensities .
So what does 60-90% of the 1RM really mean relative to our workouts?
For most people, 60-90% of their 1RM generally equates to loads where 12-2 maximum effort reps can be performed with a given weight.
When you’re lifting in the gym using a rep range of anywhere from 12 to 2 RM you can be confident that you’re activating the molecular mechanisms responsible for better strength and muscle maintenance.
For best results, some training studies suggest variation of the RM load frequently throughout a program. That is, by manipulating the RM rep range frequently through your program will speed your results.
Unfortunately, ageing appears to blunt the muscle-building effect of resistance training. The good news is, lots of other research studies show that strategic supplementation close to workouts such as in my research on Nutrient Timing will re-ignite this muscle stimulation process back to the most youthful levels. Download my Free Report on Nutrient Timing here.
The bottom line: to ensure maximal activation of muscle protein synthesis and get the best results in the shortest possible time spent training lift loads in the gym in the 12-2 RM (max-effort) rep range and supplement strategically before and after your workouts, as in Nutrient Timing.
1. Kumar V, Selby A, Rankin D, Patel R, Atherton P, Hildebrandt W, Williams J, Smith K, Seynnes O, Hiscock N & Rennie MJ. (2009). Age-related differences in dose–response of muscle protein synthesis to resistance exercise in young and old men. J Physiol 587, 211–217
2. Holm L, Reitelseder S, Pedersen TG, Doessing S, Petersen SG, Flyvbjerg A, Andersen JL, Aagaard P & Kjaer M (2008). Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity. J Appl Physiol 105, 1454–1461
3. Cribb PJ, Hayes A. Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy. Med Sci Sports Exerc. 2006 Nov;38(11):1918-25.