One of the things that drives me crazy is the misinterpretation of research results. I have most often seen this in examining physics outputs like force, impulse, or power. An example comes from the quest to identify the load for jump squats that produces the greatest power development. Much research has been done on this topic, and a variety of loads have been identified as optimum based on the power outputs that are achieved. The following summary is from Jump Squats: How Much Load?
"Research has advocated the use of certain percentages of 1 repetition maximum (1RM) of the squat to achieve the required training stimulus to develop the required levels of power. This is the first of many problems as current research is unsure of the required percentage load of 1RM. Studies by Baker, Nance and Moore suggest that maximal power is best developed at 55-59% of 1RM. McBride, TriplettMcBride, Davie and Newton concluded that the use of 30% of 1RM was best suited for the development of power, specifically in relation to velocity movement capabilities. Sleivert, Esliger, Bouroque stated that maximal power was best developed through a range of 50-80% 1RM. Stone, O’Bryant, McCoy, Goglianese, Lehmkuhl, and Schilling stated that maximal power was best developed with only 10% 1RM. How do we decipher the above to be able to decide which is the appropriate resistance level for the development of power?"
This inconsistency in the conclusions comes from variation in the research methods and in the research subjects. Is body weight included in the 1RM and the testing loads? Are the jump squats done with a free barbell or on a smith machine? What is the method of measurement? What are the instructions given to the research subject? How was the movement executed? How strong were the research subjects? These are all factors that influence the results of the research. In spite of all the variation in conclusions, people have still tried to sort through all the data and come up with a load recommendation for peak power, such as 30% of 1RM squat or 40% of total system weight. I do not have any interest in getting in on that discussion. My message is that NONE OF THIS MATTERS. Which load evokes the highest power output is irrelevant.
Why? Isn't increasing power critical to improving athletic performance? Yes, absolutely. But the load that evokes the highest power output immediately is unrelated to the load that will produce the most powerful athlete over time. The goal is not to win a contest of who can get the highest force plate reading. The goal is to make an athlete generally more forceful in sporting movements. To do this we develop strength and explosiveness. Power is just an arbitrary physics measurement, and trying to optimize it on jump squats is a completely meaningless pursuit. We need to stimulate adaptation by the body, not manipulate the load on a particular exercise to produce the highest power output right now.
Let's say we could identify the best load for power. But then we also say that athletes need to improve force production, so we find the load that produces the highest force. But then we also say athletes need to improve acceleration, so we find the best load for that. See where this is going? Which of these "ideal" loads is the correct "ideal" load? None of them. They are all completely arbitrary.
"Which load produces the highest X, Y, Z?" is the wrong question to be asking. Instead ask, "What stimulus am I trying to get out of this exercise?" For sprinting and jumping athletes, jump squats are a strength exercise. Yes, they are explosive. But if you want to train explosiveness for sports, you shouldn't be slowing yourself down with weight on your back. So jump squats are a strength exercise. Depending on the athlete and the situation, jump squats may be used to build strength, to maintain strength, or to measure force or power. If you're measuring something, pick a weight and stick with it over time. If you are training strength, and you want a stronger stimulus from jump squats, use more weight and/or drop down lower in the counter-movement. If you want less of a strength stimulus, use less weight and less knee bend. It's that simple.
To be honest I do not use jump squats very often, but for the sake of discussion let's say I choose to use them consistently with a sprinter. In the off-season we're working on strength, but I want to have a consistent measure of power along the way. I might employ jump squats with bar velocity feedback and use a load of just 40kg and natural jump depth to keep it fast. When the season comes around, we stop using heavy lifting but want to maintain power. Maybe then we keep testing with 40kg, but do some jump squats with 70kg and 2/3 squat depth to get more of a strength stimulus. Then let's say the sprinter has a minor injury and has to rehab for a few weeks. When he comes back, we want to get some strength back quickly but not slow him down with heavy deep squats. So we do some jump squats with 100kg and 2/3 squat depth to get an even greater strength stimulus. Adjustments are made based on the stimulus we want from the exercise. At no point in that process is the load that maximizes power relevant.