1. Train more frequentlyThe upper body, unlike major power muscles like the gastrocnemius (calf) and hamstrings, has substantially more slow twitch muscles. This makeup makes sense because the torso and extremities’ major rule is not to produce force, but rather serve as a conduit to transmit force into the ground to jump or into the extremities to throw an object. Slow twitch fibers also have better blood supply, allowing muscles to recover faster. Therefore, these movements can be trained more frequently in the same week.
2. Closed chain are the basicsA further Crossfit benefit is the emphasis on closed chain movements (see Sparta Point). Examples include resistance exercises that are performed against a fixed object like the bar or floor, such as pull-ups and pushups (even handstand). These exercises are often compound movements with multiple muscle groups involved, while open-chain exercises are often isolation movements that promote more shearing forces that can more easily injure joints.
3. Train for enduranceLower body endurance training, or bouts longer than 15 seconds, can be extremely detrimental to GRF; lowering jump height, sprint time, and rotational power (see Sparta Point). Fortunately, upper body exercises can provide improvements to the metabolic machinery of the muscles without negatively affecting the lower half. (see Sparta Point). Crossfit very frequently prescribes dozens if not hundreds of pull-up reps and variations over a week. They took this philosophy from gymnasts, who have upper body endurance to swing around bars/rings for almost a minute, yet how do they maintain always such phenomenal lower body power? This power to jump and flip is not from running anything over 100 meters, certainly not rowing kilometers, and definitely not performing highly skilled, heavy lifts like Olympic lifting for sets over 10 seconds. These pursuits my improve body composition and increase upper body strength, but the loss of GRF is catastrophic if you primary goal is to play a sport on the field or court.
The solution for a stronger upper body is performing heavier lower body lifts, like the deadlift and squat. The greater weights require a much larger stimulus from the trunk muscles for support. While recent research has touted the benefit of single leg resistance exercises to cause similar lower body muscle activity and testosterone responses as a squat, this study neglects the superior ability of heavier lifts to cause greater trunk/upper body muscle growth and strength. So lift your lower body heavy, you’ll improve GRF and get a stronger/bigger upper body at the same time. Efficiency is a beautiful thing. Jones, M., Ambegoankar, J., et al. Effects of Unilateral and Bilateral Lower-Body Heavy Resistance Exercise on Muscle Activity and Testosterone Response. Journal of Strength and Conditioning Research. 2012 Apr 26 (4):1094-100.