Post Activation Potentiation: This bizarre occurrence does not seem to get enough love by all the talking heads within the strength world, but that doesn’t mean you shouldn’t know about it or how to use it in your training.
In the pursuit of strength, researchers and practitioners are always looking for modalities to maximize strength (1rm) and optimize the process in which they train to elicit that strength. Post Activation Potentiation is a phenomena that is not fully understood yet; however, research literature has shown short term increases in strength and power development. PAP is an increase in muscle force production in a contraction following a non fatiguing muscle contraction. Many are familiar with exerting a large effort to lift something and subsequently becoming weaker on future concurrent lifts. This is because skeletal muscle’s performance can be affected by its contractile history. Most general lifting enthusiasts likely see this effect many times throughout the course of the training week. Their performance suffers and they cannot lift the same load they could at the beginning of their workout. This is natural and can even be optimal depending on the lifter’s goals such as hypertrophy when this level of musculoskeletal damage is indicative of adaptive change. The phenomena of PAP stands in opposition to fatigue, in that, your skeletal muscle’s performance increases after an appropriately stimulating intensity and results in both speed and power through an increase in muscle force production.
The Nitty-Gritty Ex Phys
TLDR: PAP occurs because a “conditioning” contraction allows for a tetanus state (sustained muscle contraction) to be reached at a lower frequency of action potential firing and the phosphorylation of regulatory light chains of myosin (myosin and actin filaments make up your muscle) result in higher Ca^2+ sensitivity. This means your muscle takes less effort to produce more force faster (submaximal loads)! (D.E. Rassier et al, 2000)
The mechanisms behind PAP require some prerequisite knowledge of some exercise physiology and anatomy.
Muscle and The Sliding Filament Theory
When you break muscle down into the smallest components within the muscle cell, you’re left with protein filaments known as Actin and Myosin within the Sarcomere. Sarcomeres are groups of filaments that make a muscle cell.
A contraction is started as an action potential travels down the neuromuscular chain and causes the depolarization of the sarcolemma, this causes the excitation-contraction coupling to occur which is the cellular mechanism by which Ca2 is released resulting in a muscle contraction. The myosin filament has heads on the end of them (as seen in fig.1) that have an affinity to troponin which is present on actin filaments. In order for cross-bridges to occur Ca2 must interact with troponin to allow the myosin head to complete the cross bridge and initiate a “power stroke,” or the tilting of the myosin head which then drags the myosin and actin in opposite directions. This is where the filaments are sliding across one another and the actual cause of a contraction and force generation. A breakdown of the Cross-Bridge Cycle can be seen below.
Mechanism of Post Activation Potentiation
The actual mechanism of PAP comes from the phosphorylation (attachment of a phosphor and oxygen built molecule) to the regulatory light chains of myosin. (D.E. Rassier et al., 2000) There is correlation that exists among phosphorylation and potentiation. Potentiation of the muscle fiber is shown by an increase in the force of the contraction at a given submaximal Ca2 concentration, meaning it is taking less Ca2 in the muscle to stimulate harder contractions, this is calcium sensitivity. (Persechini A et al., 1984) The enzyme responsible for the phosphorylation of myosin filaments is myosin light chain kinase (MLCK) which is activated when Ca2 concentration rises (not as a result of SERCA and peripheral muscle fatigue) and the Ca2-calmodulin complex binds to MLCK. In this environment, the increased calcium sensitivity enhances submaximal contractile response which in turns allows for more force production and rate of force development at submaximal intensities or loads.
It must be mentioned that potentiation of the muscle is at ends with peripheral fatigue, meaning that, to create an environment of fatigue or potentiation, you must take the same proverbial road by heavier muscle contractions. The very thin line separating the two is at what point you stop and how close can you get to the line without crossing it. Peripheral Fatigue is outside the scope of this article and would require one or two on its own as a topic.
Practical Application
We’ve discussed enzymatic processes and anatomy and identified what exactly is occurring during post activation potentiation, but you might be wondering about how to actually utilize what you’ve learned. Well, when bringing this topic into the weight room the lifter could create an environment for PAP to occur by performing a heavy set of an exercise such as a squat or deadlift around 80-95% of 1rm for 1-5 reps, being sure to stay away from technical failure; then performing a sub maximal exercise such as a plyometric box jump or “back off volume work,” in a similar exercise that was used in the beginning. However, PAP can’t be used to elicit a single improvement of 1RM due to the nature of it’s prerequisites. Since it allows for increased performance intra workout, PAP is a fantastic tool that can allow more volume to accumulate, ultimately leading to more adaptation and subsequently strength. It is important to keep the sets leading up to PAP are non-fatiguing as any amount of fatiguing muscle contraction will lead to impaired force production from the muscle contraction. Many lifters anecdotally love training with “back off” sets. Due to the prerequisite factors needed to create the opportunity for PAP to occur, beginning lifters might struggle to find the correct loading parameters for themselves since untrained individuals will have a higher chance of fatigability. That’s not to say that it can’t happen and that many sports therapists and strength and conditioning professionals can achieve good results with untrained clients.I hope you enjoyed this article and if you learned anything or took away any value please remember to share!
Citations (Continued Readings)
Rassier, D.E., & MacIntosh, B.R.. (2000). Coexistence of potentiation and fatigue in skeletal muscle. Brazilian Journal of Medical and Biological Research, 33(5), 499-508. https://doi.org/10.1590/S0100-879X2000000500003Persechini A, Stull JT. Phosphorylation kinetics of skeletal muscle myosin and the effect of phosphorylation on actomyosin adenosinetriphosphatase activity. Biochemistry. 1984 Aug 28;23(18):4144-50. doi: 10.1021/bi00313a021. PMID: 6237685.