Strength and Capacity

There is considerable confusion about the roles of strength and capacity in MetCons which use barbells - or dumbbells - for high reps. Are these strength workouts? Engine workouts? What’s the best way to train for improved performance in these MetCons? This article attempts to answer these questions and more. As always, the purpose is to continue discussion, not end it. First, some definitions:

Strength is the ability to produce and transmit force, generally to an external object.

Capacity is the ability to produce ATP via the body’s energy systems. Conditioning refers to activities which increase capacity.

There is little published literature featuring direct scrutiny of CrossFit© benchmark WODs or similar training styles. One such study concluded that the CrossFit© total explained 77% of the variance in benchmark WOD Grace. In other words, the study shows that strength is the most powerful performance predictor at Grace. Anecdotal evidence further supports the influence of strength. Rich Froning and Dmitry Klokov are extremes in capacity and strength, respectively. Each has completed the benchmark WOD Isabel (30 snatches) at ~225lbs. In a high-adrenaline environment which should promote performance, Rich finished in 4:35. This is a magnificent time that few athletes can match. Yet Klokov was done in 3:35, a full minute faster.

While this comparison is far from scientific, Klokov’s advantage at 30 reps is arguably as commanding as his advantage at one rep. Rich’s capacity could not overcome the strength gap. Additional anecdotes abound. One of our favorites is Brian Shaw completing Grace.

Does capacity matter at all FOR these workouts?

With limited evidence available, we turn to physiology. Lifting for reps activates the glycolytic system, producing lactic acid. If too much lactic acid accumulates, the system temporarily shuts down. Lactic acid accumulation is governed by lactate production and lactate removal.

Lactic acid removal: Removal occurs via (1) the Cori cycle, wherein lactate is transported to the liver, converted to glucose and transported back to muscles and (2) oxidation. Both processes are positively correlated with aerobic capacity. Aerobic conditioning increases capillary density around working muscles, enhancing lactic acid transport out of muscle cells. Conditioning also increases the volume-density of mitochondria in other muscle cells, providing increased capacity to oxidize lactate. (We've simplified. For the curious reader, there are links to more detailed analyses at the end of the article.)

Lactic acid production: Lactic acid is produced by glycolysis in working muscle cells. Motor units - groups of muscle cells and fibers - are activated in ascending size order. The brain activates what is needed and conserves the remainder. As the need for force increases, additional fibers are recruited. For sustained activity, the brain attempts to cycle the recruitment of muscle fibers to permit rest and delay fatigue.

Because Klokov is stronger, he likely performs the lifts with fewer motor units activated. Therefore, he produces less lactic acid and can work at a higher sustained rate than Rich, despite Rich’s considerable capacity advantage. A broader generalization of this conclusion means:

Performing reps at a high percentage of your 1RM will require activation of more motor units than at a lower percentage. Reps at a high percentage of 1RM produce lots of lactic acid, quickly shutting down the glycolytic engine. We believe that limiting lactic acid production is more important to performance in MetCons with lots of barbell reps than maximizing its removal. Therefore, we advise our athletes that the fastest way to improvements in barbell workouts is by increasing their 1-rep maxes.

Conclusion:

The scientific evidence, while limited, shows a clear relationship between strength and performance in MetCons with high rep barbell lifts. Anecdotal evidence featuring two elite athletes with vastly different capabilities provides additional evidence, and a physiological explanation seems to at least partly predict this phenomenon. While the well-developed fitness athlete must emphasize conditioning as a central component of their training regime, athletes who wish to improve their performance in MetCons featuring lots of barbell lifts should devote additional time to strength training.

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