In the discussion on transfer of training, squat depth is a hotly contested issue with many opinions clouding the view. On one side many people testify to superior strength and hypertrophy gains from deep squatting. Particularly compelling examples of this come from the sport of weightlifting. It's easy to look at the successful strength and power development of these athletes and conclude that deep squatting is best. On the other side people like to point out that sprinting and jumping do not involve deep knee and hip flexion and conclude that partial squats are more transferable to sports movements. Particularly in the track and field world a lot of athletes utilize half or quarter squats, because top speed sprinting and running jumps off one leg use feature relatively small knee bend. Then we have an array of other opinions. Some say range of motion is good, but we should stay above parallel for lower back health. Others say 90 degrees of knee and hip flexion represents an optimal range. Others say the deep squat is a fundamental human movement and should therefore be the foundation of strength training. From a theoretical standpoint, it's easy enough to latch onto any one of these opinions, so reaching a conclusion requires looking at some hard science and relying on experience.
Looking at different squat depths, the coordination is similar. It's bilateral ankle, knee, and hip extension and spinal anti-flexion against a load. A key difference is muscle length. A deeper squat lengthens the glutes and quads more. We need to consider the structural and neurological effects of training at short and long muscle lengths.
STRUCTURAL
First consider the length tension curve of muscle. This is simple anatomy and physiology. Muscles produce greater tension at longer lengths. (If you're not familiar with this, check out this video.) Greater tension produces more tissue breakdown and greater structural strength in muscles and tendons. Squatting deeper lengthens the quads and glutes further, which elicits greater muscle tension. Does a deep squat below parallel lengthen the muscles too far? For that answer refer to the video below.
Now consider knee and hip loading. Squats above parallel are typically executed with relatively more backward hip movement and less forward knee movement. This reduces knee extension demands and neglects the quadriceps. On the other hand deep squatting naturally involves more forward knee movement and places much greater stress on the quadriceps while certainly not neglecting hip extension and the glutes. Deep squats offer more balanced strengthening of hip and knee extension.
Because of range of motion and knee loading, deep squats offer a superior structural strength stimulus compared to partial squats. This is not up for debate. We can know this based on physics and muscle physiology without actually having to test it, but for good measure there is plenty of research to support the claim that greater range of motion in strength training produces greater structural development. Here is an example with squat depth.
Effect of range of motion in heavy load squatting on muscle and tendon adaptations.
However, we do have to be aware of specificity. Strength training at long muscle lengths is a very different stimulus than sprinting and jumping. That means it will carry with it different adaptations, including some that might be disruptive to some measures of athleticism. For example, the distal quadriceps hypertrophy that can result from deep squatting is something that many people would say should be avoided when pursuing top end sprint speed. We won't get into specifics on this particular topic, but we do have to acknowledge the principle: different stimuli produce different adaptations. To clarify, deep squats are a superior GENERAL structural strength stimulus.
It is key to understand, though, that this does not mean that partial squats cannot work really well. It is entirely possible for one person to do partial squats and grow their quads and glutes more than someone else who squats deep. A greater stimulus does not guarantee greater results, because the stimulus is only one of many factors (training history, nutrition, sleep, age, genetics, gender, just to name a few). We can know that deep squatting offers a superior structural strength stimulus, but that doesn't mean an average guy who deep squats for 10 years will have stronger quads than a genetic freak 17-year old who does half squats. The stimulus is just one factor.
NEUROLOGICAL
Now let's consider neurological factors and training transfer. A fair amount of research has been done on the adaptations to strength training at different joint angles. The results do show a pattern of specificity. People tend to get stronger specifically near the joint angle at which they train more than at other angles. However training at longer muscle lengths tends to improve strength at shorter muscle lengths more than training at shorter lengths improves strength at longer lengths. The adaptations to training at longer muscle lengths are more general. We'll review a few studies.
What is the source of joint angle specificity? Some evidence suggests that part of the explanation is changes in neural drive at the targeted joint angle.
The research subjects were broken up into three groups that did isometric knee extension training at 30, 60, and 90 degress of knee flexion. The greatest increase in strength occurred at the specific joint angle, but the longer muscle length training transferred to shorter muscle length more than vise versa. This led the researchers to conclude "Further analyses indicated that exercising in the lengthened position for the quadriceps femoris muscles (90 degrees of knee flexion) produced increased torque across all angles measured and appeared to be the more effective position for transferring strength and EMG activity to adjacent angles..."
While training at 90 degrees of flexion did transfer better, training at 30 and 60 degrees still did produce greater increase in neural drive at the targeted angle. Does that mean it would also produce greater improvement in athletic movements that utilize similar knee angles? That research was done with isometric knee extension. Can we expect the same results with dynamic multi-joint movements? Here's a study that explored changes in activation and other measures in response to reaching different depths in the back squat, leg extension, leg press, bulgarian split squat, and forward lunge.
In this case the change in activation was similar. Specificity was present, but training with more range of motion did transfer to less ROM. What’s interesting is the short ROM training actually decreased quadricep activation at all joint angles. Instead of increasing activation more at the targeted angle, it just decreased it less (black bars in the graph below). These results still fit the pattern, although the decrease in activation does raise some questions. After considering all measures, the researchers concluded, "Following a prolonged period of resistance training (i.e. an accumulation of training bouts), we show that long-length trained muscle exhibits relatively greater muscle activation, neuromuscular efficiency, and hypertrophy compared with its short-length trained counterpart. Similarly with detraining, long-length training was associated with a greater retention of improvements in muscle characteristics."
Considering the research, it's pretty clear that strength training at longer muscle lengths produces generally better neuromuscular adaptation. Whereas training at short muscle lengths produces some specific results with general adaptations that are typically lacking. But we still have to figure out whether or not the specific adaptations have value. It is definitely understandable how people can look at these results and see a need for strength training at sport specific joint angles. But consider this...
If the adaptation does not transfer to other joint angles, can we expect it to transfer to other contraction velocities or time frames?
If the training does not make the neuromuscular system generally better at producing force, how can it transfer to other movements? You can choose to disagree, but I interpret these results as indicating that specific strength increase results from familiarity with the movement and improved skill, not any changes to transferable qualities. Perhaps if I have never done any training that targeted 50 degrees of knee flexion, doing squats to that angle would have value. But if I have already executed 10,000 jumps at that knee angle in my life, do I also need to develop the skill of squatting to that angle? Probably not. What I need is for squatting to make me generally more forceful. This echoes my previous article, which addressed specific strength training as a whole. In that article I established that there is a clear need for specific training. However the ultimate specific training for a sport is the sport itself. Assuming that is in place, strength training can only be effective by making an athlete generally stronger.
PERFORMANCE RESEARCH
From a theoretical standpoint, this is how one can conclude that deep squats offer a stimulus that is both structurally and neurologically superior to partial squats. But let's get past theory. What happens in practice? One limitation of the research presented so far is that it only investigated knee flexion to 90 degrees. This next research compared quarter squats to front and back squats below parallel, which typically use 120+ degrees of knee flexion.
Influence of Squatting Depth on Jumping Performance
Feel free to check out the details, but the results were clear. Squatting below parallel increased strength in deep and quarter squats and increased jumping ability. This was without the presence of any specific training. What would the results have been if deep squats were combined with some jumping practice or plyos? Quarter squats produced huge improvements in quarter squat strength but no increase in deep squat or jumping ability. That definitely calls into question the value of joint angle specific strength gains. Another interesting point is that muscle activation was again decreased after quarter squat training.
The subjects in that research were relatively weak with deep squat maxes below 1.5 times body weight or even below body weight. What if athletes are already strong? Some people in the sports training field have theorized that athletes should begin by developing a decent level of general strength but eventually switch over to more specific strength training. If specific strength adaptations have value, I fail to see why they would be any less valuable to weaker athletes, but let's entertain this idea. Into this discussion steps a study conducted on collegiate athletes who already squat 1.5 times body weight.
Joint-angle Specific Strength Adaptations Influence Improvements In Power In Highly Trained Athletes.
The objective was to examine if athletes who already possess a decent level of general strength would see better transfer to speed and jumping from using partial squats. They did 16 weeks of training where squat and power clean made up 90% of the training volume with some insignificant assistance work being the last 10%. On the surface, the results seem to indicate that quarter squat training was decisively superior to squats to 90 degrees and squats below parallel. The working theory is that the specific adaptations to partial squatting transferred to improved sprinting and jumping because of joint angle specificity. Let me offer a different take.
We have to acknowledge that there is huge disconnect between strength and explosive athletic movements. This disconnect becomes more prevalent as athletes get stronger and more athletic. When beginner athletes build strength it often produces immediate athletic improvements across the board. Intermediate or advanced athletes on the other hand may experience stagnancy or even decrease in athleticism while they are getting stronger. In order to produce athletic improvements from increased strength, it is often necessary to use a period of training focused on fast movements.
Now let’s talk about American football players who made up 24 of the 28 research subjects. Football has a culture in which being big and strong is highly valued to the point where athleticism is often not maximized. By the time they are adults, a lot of football players boast impressive strength numbers but not the speed and jumping ability that you would hope for given how strong they are. In this situation they need to get away from strength training in order to make athletic gains. Here’s an example of this scenario in a football player who contacted me.
The main thing between me and my dream of playing D1 football is my physical abilities when it comes to speed and agility. I am not slow (4.65 40 hand-time), but am definitely not where I want to be… I have done strength training since eighth grade and am strong for my size (back squat of 350 and squat-clean of 242 @ 160 lb.), so I believe I have adequate strength “potential” to make athletic gains in terms of speed. What I am so curious about is your concept of periodization where an athlete stops lifting and does solely explosive work to essentially increase muscle speed (basic way of putting it). I’ve tried this for about a month now, and I definitely have gotten faster with only doing sprinting and plyometrics...”
As a coach in Texas, I see this in football players all the time. In middle school, kids are growing, lifting, playing sports, and getting stronger, and they tend to get steadily more athletic during that time. But in high school this process slows down. In the early off-season players are lifting a lot at school, and some of the better athletes get slower during this time. It's not until spring ball rolls around and guys get a break from lifting that they see athletic improvements. This happens already in high school sophomores.
With these things in mind, if you tell me that a bunch of college football players are going to do deep squats for 16 weeks in a row, I am not going to expect them to be sprinting faster at the end of that. On the other hand if you tell me that college football players are going to do minimal strength training for 16 weeks and do some power clean for maintenance, I would expect those guys to get faster during that time. For a lot of football players the best way to get immediate results is to stop strength training. This is essentially what the quarter squat training group did. I believe the quarter squats in this study were an insignificant stimulus. At the same time, if the deep squat group followed up the research protocol with 16 weeks of not squatting at all, I would expect them to see some excellent athletic results.
In my opinion, what we see in this study is two groups (the half and deep squat groups) who built some potential for athletic gains by getting stronger but have had no chance to realize that potential and the quarter squat group who has pretty much stopped strength training and maximized athleticism at their current strength level. Of course if you want to believe that joint angle specific strength gains transferred better to sprinting and jumping, you can choose to do that.
Some other points about the study...- We are left in the dark on the explosive training of the subjects. Were they sprinting and jumping regularly? Just playing their sport? The presence or lack of specific training makes a big difference.
- There were 4 random subjects (1 wrestler, 1 track athlete, and 2 basketball players) mixed in with the football players. They should have been left out as this only brings in more variables, especially when we have no info on explosive training. If the wrestler is just lifting and practicing wrestling, can we expect his vertical jump to improve? If the basketball players are just lifting and playing basketball, can we expect their linear speed to improve?
- Consider the fatigue factor. Deep squats are an extremely strong stimulus, which brings potential for nervous system fatigue. What if that group deloaded for a month?
- The deep squat group increased max by an average of 17% but saw no improvement in standing vertical. This only seems possible if these subjects were completely lacking specific jump training and/or severely fatigued.
- Where is the control group that does no squats but still does the other training? I believe this group would have seen excellent results.
- As usual with research, we don't get to see individual characteristics of the subjects or individual results. This would provide far more insight, which is why coaching individuals over time leads to much greater understanding than research alone.
- The quarter squats were done to 55-65 degrees of knee flexion. The half squats were done to 85-95. If joint angle specificity was responsible for the athletic improvements, the half squat group should have seen the best jumping results, because athletes with strength training background typically get near or even beyond 90 degrees of flexion in a standing vert. Check out this instagram post.
CONCLUSIONS
Because I believe that general strength is the purpose of strength training, I opt to use deep squats regularly. I also use other squat variations for variety. Deep squats are the best general strength stimulus, but this does not mean that partial squats cannot work. It may be a lesser stimulus, but sometimes a lesser stimulus can be really effective, because again the stimulus is only one of many factors. We could say that lifting 50% of 1-rep max is a lesser stimulus than lifting 90%. But sometimes people can get a lot stronger with light weights. And if we're talking about transfer to athleticism, getting stronger with light weights should produce better results because the lifting is lighter, faster, and less disruptive to explosive abilities. In the same way, partial squats are a lesser stimulus, but the right person in the right situation can still see drastic improvement in general strength from partial squats. For example, the vast majority of teenage male athletes do something less than a full squat. They may try to get to parallel, but few actually do. And yet teenage males typically do get stronger and more athletic. I myself used a routine of jumping, stretching, calf raises and squatting above parallel to add about 12 inches to my vertical in less than a year when I was 13 years old. I also grew 4 inches during that time. After that period, I had little success until another growth spurt when I was 15. At that time I used the same exercises plus some plyometrics and gained 5-6 inches on my vertical in a couple months. Not long after that I experienced jumper's knee for the first time and dealt with it on and off for 8 years until I learned how to squat deep at age 24. I also never got stronger again squatting above parallel. Looking back I believe I could have gotten superior athletic results and avoided knee pain had I used deep squats from the beginning.
I absolutely acknowledge that partial squats can be effective in some situations. The same is true of jump squats, olympic lifting, plyometrics, or even just playing sports without additional training. But in order to keep building strength long term, most of us who are not genetic freaks need to resort to a more powerful stimulus, namely heavy, full range of motion strength training. Deep squat, hinge, and lunge variations are the go to exercises.
I also acknowledge that heavy, full ROM strength training is quite different than athletic movements, and that can make it disruptive to explosive abilities. Some people attempt to deal with those differences by turning to more specific strength training options. I understand the rationale behind using partial squats, but I highly value the strength building capabilities of deep squats. Compared to partial squats, I have found that deep squats produce greater strength increases that last longer without having to do as much work. Rather than abandoning deep squats because of their potential to interfere with explosive abilities, I try to use a different means of dealing with that issue, so I can still harness their power. I deal with the challenges of training transfer by taking breaks from strength training to maximize explosive abilities and take advantage of delayed training effects. I have lots of content on this.
In the process of maximizing athletic ability, I may use what people call more specific strength training. I don't do this because I expect specific strength adaptations to have value. Rather I am trying to maintain general strength while being less disruptive to athleticism.
Case Study
Max velocity sprinting is the athletic measure that is farthest away from deep squatting if we look at contraction velocity, time frame, joint angles, structural demands, etc. So deep squatting can be most disruptive to top end speed, and getting transfer from deep squats can be difficult. And yet, by (1) continuing to use the ultimate specific sprint training (sprinting) during a period of general strength development and (2) utilizing a break from general strength training, the potent stimulus of deep squats can still be used successfully. Here is an example of that process in a female sprinter. She had an intermediate strength level (1.7 x BW deep squat) and borderline elite top end speed for her height. In the video, she was only three weeks removed from heavy deep squatting. She was beginning to display the benefits of her improved strength level, but her speed potential certainly had not been fully realized.
In Summary
- Specificity exists, and it has major implications on athletic development.
- The best specific training for sprinting and jumping is sprinting and jumping.
- The purpose of strength training is getting generally stronger.
- If you can get generally stronger from partial squats, it will probably work very well for athletic development although possibly not as well for injury prevention.
- Long term you will likely need to resort to deep squats, the ultimate general strength training.
- Deep squats are very different from sprinting and jumping, and can be disruptive to explosive abilities.
- Utilize smart periodization to effectively harness the potent stimulus of deep squats.