Key differences in approach
The fluid lifter works primarily to time, not to reps. There is a natural cadence that is right for each person, and that varies according to conditioning and control of the body.
In the fluid style, the muscles of the girevik (kettlebell lifter) have to be able to recover ATP stores while holding the KB. This means that he or she is working while resting. This quality of resting under load is a demand unique to kettlebell lifting among the competitive lifting sports.
In many other forms of athletics as well, there is a prominent need for relaxation under load. A prime example is in the fighting sports, which require the ability to relax and recover while subject to external stressors. The relaxed, natural manner of FS lifting is consistent with athletic movements. The signature of a trained athlete is fluidity and grace, an effortless quality of motion.
The RS approach, in contrast, generally focuses on reps, not on time. Typically the goal is reps done as fast as possible. While this is a demanding task and quite admirable, there is a limiting factor because once you approach your anaerobic threshold; you will not be able to continue.
The difference in the quantity of work that can be accomplished in each style, RS vs. FS, becomes very obvious when the sets are extended over a full ten minutes, which is the duration of time given to complete your reps in a competition.
A rigid-style practitioner may be able to do 25 rpm but will be able to sustain that effort for only a few minutes, because of the fast pace and the amount of tension held in the muscles. He or she will tire and lose power very quickly. For example, a well-conditioned RS athlete may be able to last at that pace for as long as four or five minutes. When the set is over, he or she may have 125 total reps.
On the other hand, a fluid-style athlete who maintains patience and a controlled pace may move slightly slower, so that he or she has a chance to breathe and rest after each rep. This athlete moving at the more moderate pace of 20 rpm will likely be able to sustain the effort for twice as long. At this slower pace he or she will have completed 200 reps with the same load. This is the way of pacing, and as it extends out, the pacing will allow much greater volume per set and overall.