Whether you do 5 sets of 5, 3 sets of 10 or 3 sets of 1 will depend upon the ultimate goal of your training, as well as whether you are a novice, intermediate or advanced athlete.
Power, strength, and hypertrophy training exist on a continuum based on the number of reps performed each set (and therefore the intensity of the load lifted – lower reps = heavier weights lifted and vice versa). Sets of 1 to 3 reps are best for improving strength and power, while sets of 10 are best for causing hypertrophy – the muscle swelling that bodybuilders are all after. This is the reason why so many people do 3 sets of 10 in most gyms, because they’ve heard that bodybuilders lift that way and they want bulging muscles.
However, CrossFitters are more interested in functional strength and power – attributes that are much more useful outside of the weight room. So, Steel City CrossFit recommends that athletes focus their lifting efforts on sets of 5 or less.
For a novice athlete, 5 sets of 5 (not including warm-up sets) gives the best balance between strength and hypertrophy. The weights that can be handled in a 5×5 scheme cause increases in muscle contractile power (strength) while also causing the muscle fibers to swell, allowing for more contractile protein to be added.
Once the effectiveness of a 5×5 program begins to plateau, focus can shift to sets of 3 and 1 to maximize strength and power gains. Once a program of 5×3 and 5×1 rep sets has been tapped, an advanced athlete who is focusing on strength training would then go on to a period of hypertrophy training (typically 3-5 sets of 10 reps). Allowing for a hypertrophy phase allows the muscles to grow in size, which provides room to add more contractile protein through sets of 5 or fewer reps.
CrossFitters tend to focus their lifting efforts on sets of 5 or less, with variety mixed in so that they aren’t always focusing on one rep scheme for an entire training phase. Sets of higher reps with lighter weights tend to show up during the met-con and strength endurance WODs as well, so they usually don’t need to be addressed separately.