CUP CHECK!!
Thursday, May 31, 2012
Saturday, May 26, 2012
Single Leg Squats: Patellofemoral Implications
There has been a lot of intrigue/argument on the internet about the use of single-leg exercises versus bilateral exercises (i.e. standing on one foot vs. standing on both feet) and the development of lower body strength. Here is a video of both for you visual learners:
Bilateral Barbell Squat
Note: If you listen closely, you can hear Pantera's "Cowboys from Hell" playing in the background. I told you in the previous post that Pantera was good lifting music!
Unilateral Split Squat
That video shows a rear-foot elevated split squat (aka bulgarian split squat) using dumbbells. Of course, you can use a barbell with a variety of grips (across the shoulders behind the head, clean grip, overhead, etc.) when performing this variation. I am not sure which squat (uni vs. bi) is "better"; and I don't think there really is an answer to that. As I have learned in my two semesters of physical therapy school, the answer to which one is better than the other is "it depends". I am going to share some opinions of those smarter than myself, some research findings, and some anecdotal evidence from my own experiences.
What Do Strength Coaches Have to Say About It?
Ben Bruno posted a great anecdotal study he performed on himself about the use of rear-foot elevated splits squats and how it impacted his lower body strength. In case you didn't read the article, he found that once he was able to adequately adjust to the increased stability demands of having a much smaller base of support, he was able to progress from holding 40 lbs. dumbbells to supporting a 275 lbs. barbell on his back. He completed 5-6 sets of 6-8 reps of unilateral squatting, followed by a bilateral glute ham raise. Following 15-months of this routine he re-assessed his bilateral squat strength, and found that his maximum number of total repetitions of 225 lbs. increased from 21 reps to 35. His max barbell hack squat improved from 385 x 5 to 405 x 5 and his vertical jump increased by 2 inches.
Mike Boyle, a longtime strength coach for various college and professional athletes and teams, has been singing the praises of unilateral leg training since at least 2007. He has come under fire for some of his views regarding the back squat, but this isn't exactly the forum to discuss that as most of his points are regarding lower back issues. Nevertheless, he is not alone when discussing the merits of single leg training. Mike Robertson and Eric Cressey have both provided excellent exercises and talking points on the topic, as well. There seems to be a consensus opinion that single-leg training can be effective for building lower body strength, but no matter how strong you get on one leg you'll never be as strong as you are on two.
Specific to the knee and patella, however, is the need for reduced stress to the tibiofemoral and patellofemoral joints when squatting. The adage has always been to keep the "knees behind the toes" when squatting. While that does make sense, a 2003 study by researchers at the University of Memphis concluded that "restricting forward movement of the knees may minimize stress on the knees,it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly
past the toes (1)". I think the big picture, take home message when bilateral squatting is to initiate the movement by sitting back with the hips and not bending at the knees. This should result in the weight being on the heels as opposed to the toes and forefoot.
In an effort to keep the knees completely vertical and behind the toes, the low back often rounds resulting in a loss of natural curve (lordosis) and potential for increased disc pathology. Increasing the depth while maintaining the weight on the heels also requires sufficient flexibility of the calf muscles, as greater dorsiflexion is required to keep the weight on the heels.
In a split stance, the pelvis will be stabilized or move into anterior tilt. While anterior tilting is not ideal, it is much less likely for a disc to herniate anteriorly with anterior tilt/lumbar extension than with posterior tilt/lumbar flexion.
Personally, in either a split squat with the rear foot elevated or on the ground, I find it easier to "sit back" and maintain a vertical tibia in the leg supporting the weight. Mike Robertson refers to this as the "90/90 split squat" with a 90 degree angle at the knees and the hip of the rear leg (pictured below).
As you can see, the tibia of the leading/supporting leg is almost perfectly vertical. Patellofemoral compression increases when two things occur: an increase in the angle of knee flexion, and when the quadriceps generate force. In the picture, knee flexion is approximately 90 degrees, which generates high compressive forces. However, with the tibia vertical, this is minimized. Why? Because the patellar tendon and quadriceps tendon drive the patella into the trochlea (groove between the condyles of the femur) with increased knee flexion. If you go into a squat position on your toes, as a baseball catcher does, the quadriceps tendon (superiorly) and patellar tendon (inferiorly) both produce a large resultant force vector forcing the patella into the trochlea and creating high compressive forces. This is shown by the large red arrow in the picture below:
Source: http://www.mikereinold.com/2009/06/biomechanics-of-patellofemoral.html
What Does the Research Say?
Research by Rafael Escamilla, PT, PhD, CSCS, FACSM, a Professor in the Department of Physical Therapy at California State University - Sacramento has shown in several studies that patellofemoral forces are greater in bilateral than unilateral squats. Bilateral squatting was shown to produce slightly over 4,000 Newtons on the patellofemoral joint in the eccentric (lowering) portion of the squat at 90 degrees of knee flexion (2). To put that in perspective, 4,000 N is approximately 5 x bodyweight, which is similar to what a person experiences when going downstairs (3).
Escamilla, et al. also investigated the effects of a long step versus a short step while performing a lunge with and without a stride (4). For the purposes of this blog, I will only comment on the results of the lunges without a stride (meaning that both feet are stationary, as one would perform in a split squat). The differences in step length, which essentially means that a short step allows the tibia to be less vertical and increase the shear and quadriceps activity, whereas the longer step keeps the tibia vertical and involves more glute activity (i.e. "sitting back").
2.) Escamilla RF, Fleisig GS, Zheng N, et al. Effects of technique variations on knee biomechanics during the squat and leg press. Medicine & Science in Sports & Exercise. 2001:1552-1566.
3.) "Biomechanics of Patellofemoral Rehabilitation". MikeReinhold.org. http://www.mikereinold.com/2009/06/biomechanics-of-patellofemoral.html. Retrieved May 25, 2012.
4.) Escamilla RF, Zheng N, Macleod T.D., et al. Patellofemoral joint force and stress between a short and long-step forward lunge. Journal of Orthopedic and Sports Physical Therapy. 2008;38(11):681-690.
5.) Escamilla RF, Zheng N, Macleod TD, Edwards BW, Imamura R, Hreljac A, Fleisig GS, Wilk KE, Moorman CT, Andrews JR. Patellofemoral Joint Force and Stress during the Wall Squat and One-Leg Squat. Medicine & Science in Sports & Exercise. 2009; 41 (4): 879-890.
Bilateral Barbell Squat
Note: If you listen closely, you can hear Pantera's "Cowboys from Hell" playing in the background. I told you in the previous post that Pantera was good lifting music!
Unilateral Split Squat
That video shows a rear-foot elevated split squat (aka bulgarian split squat) using dumbbells. Of course, you can use a barbell with a variety of grips (across the shoulders behind the head, clean grip, overhead, etc.) when performing this variation. I am not sure which squat (uni vs. bi) is "better"; and I don't think there really is an answer to that. As I have learned in my two semesters of physical therapy school, the answer to which one is better than the other is "it depends". I am going to share some opinions of those smarter than myself, some research findings, and some anecdotal evidence from my own experiences.
What Do Strength Coaches Have to Say About It?
Ben Bruno posted a great anecdotal study he performed on himself about the use of rear-foot elevated splits squats and how it impacted his lower body strength. In case you didn't read the article, he found that once he was able to adequately adjust to the increased stability demands of having a much smaller base of support, he was able to progress from holding 40 lbs. dumbbells to supporting a 275 lbs. barbell on his back. He completed 5-6 sets of 6-8 reps of unilateral squatting, followed by a bilateral glute ham raise. Following 15-months of this routine he re-assessed his bilateral squat strength, and found that his maximum number of total repetitions of 225 lbs. increased from 21 reps to 35. His max barbell hack squat improved from 385 x 5 to 405 x 5 and his vertical jump increased by 2 inches.
Mike Boyle, a longtime strength coach for various college and professional athletes and teams, has been singing the praises of unilateral leg training since at least 2007. He has come under fire for some of his views regarding the back squat, but this isn't exactly the forum to discuss that as most of his points are regarding lower back issues. Nevertheless, he is not alone when discussing the merits of single leg training. Mike Robertson and Eric Cressey have both provided excellent exercises and talking points on the topic, as well. There seems to be a consensus opinion that single-leg training can be effective for building lower body strength, but no matter how strong you get on one leg you'll never be as strong as you are on two.
Specific to the knee and patella, however, is the need for reduced stress to the tibiofemoral and patellofemoral joints when squatting. The adage has always been to keep the "knees behind the toes" when squatting. While that does make sense, a 2003 study by researchers at the University of Memphis concluded that "restricting forward movement of the knees may minimize stress on the knees,it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly
past the toes (1)". I think the big picture, take home message when bilateral squatting is to initiate the movement by sitting back with the hips and not bending at the knees. This should result in the weight being on the heels as opposed to the toes and forefoot.
In an effort to keep the knees completely vertical and behind the toes, the low back often rounds resulting in a loss of natural curve (lordosis) and potential for increased disc pathology. Increasing the depth while maintaining the weight on the heels also requires sufficient flexibility of the calf muscles, as greater dorsiflexion is required to keep the weight on the heels.
In a split stance, the pelvis will be stabilized or move into anterior tilt. While anterior tilting is not ideal, it is much less likely for a disc to herniate anteriorly with anterior tilt/lumbar extension than with posterior tilt/lumbar flexion.
Personally, in either a split squat with the rear foot elevated or on the ground, I find it easier to "sit back" and maintain a vertical tibia in the leg supporting the weight. Mike Robertson refers to this as the "90/90 split squat" with a 90 degree angle at the knees and the hip of the rear leg (pictured below).
As you can see, the tibia of the leading/supporting leg is almost perfectly vertical. Patellofemoral compression increases when two things occur: an increase in the angle of knee flexion, and when the quadriceps generate force. In the picture, knee flexion is approximately 90 degrees, which generates high compressive forces. However, with the tibia vertical, this is minimized. Why? Because the patellar tendon and quadriceps tendon drive the patella into the trochlea (groove between the condyles of the femur) with increased knee flexion. If you go into a squat position on your toes, as a baseball catcher does, the quadriceps tendon (superiorly) and patellar tendon (inferiorly) both produce a large resultant force vector forcing the patella into the trochlea and creating high compressive forces. This is shown by the large red arrow in the picture below:
Source: http://www.mikereinold.com/2009/06/biomechanics-of-patellofemoral.htmlIn the image above, Fq is the quadriceps tendon force and Fp is the patellar tendon force. As you can see, if the Fp is maintained relatively vertical (i.e. weight on heels), it will contribute less to the total posteriorly directed, compressive force of the resultant red arrow (vector), and the compressive force will not be as great.
What Does the Research Say?
Research by Rafael Escamilla, PT, PhD, CSCS, FACSM, a Professor in the Department of Physical Therapy at California State University - Sacramento has shown in several studies that patellofemoral forces are greater in bilateral than unilateral squats. Bilateral squatting was shown to produce slightly over 4,000 Newtons on the patellofemoral joint in the eccentric (lowering) portion of the squat at 90 degrees of knee flexion (2). To put that in perspective, 4,000 N is approximately 5 x bodyweight, which is similar to what a person experiences when going downstairs (3).
Escamilla, et al. also investigated the effects of a long step versus a short step while performing a lunge with and without a stride (4). For the purposes of this blog, I will only comment on the results of the lunges without a stride (meaning that both feet are stationary, as one would perform in a split squat). The differences in step length, which essentially means that a short step allows the tibia to be less vertical and increase the shear and quadriceps activity, whereas the longer step keeps the tibia vertical and involves more glute activity (i.e. "sitting back").
Forward lunge with short step
Forward lunge with long step (note the reduced dorsiflexion with a long vs. short step)
Not surprisingly, the longer step stationary lunge produced less maximum patellofemoral compression at 90 degrees of flexion than did the stationary lunge with a shorter step (~2000 N vs. ~3000 N) (4). This makes sense biomechanically, as the shorter step produces more of a posteriorly directed force on the patella as both the quadriceps tendon superiorly and the patella tendon posteriorly are pulling the patella deeper into the trochlea. With a longer step, the tibia is able to remain more vertical and the resultant vector from patellar tendon pull is reduced.
Interestingly, another study by Escamilla et al. also found that a one-legged squat produced less patellofemoral compressive forces than a bilateral squat with the participant's back supported by the wall with both a short and long step (5). This was counter to their hypothesis that the one-legged squat would have the highest compressive forces. It is worth noting though that in all studies with bilateral squatting a greater load was used in comparison to unilateral exercises.
So What?
Hopefully it appears that both exercises can generate increased strength in the lower extremity.
I have employed both unilateral and bilateral versions in my workouts since coming back to the gym after dislocating my knee cap in 2006 and undergoing surgery to realign the patella and clean out the torn pieces of articular cartilage and bone that was sheared off during the injury.
Not surprisingly, I am very cautious when it comes to my lower body workouts now, and I "listen" to my knees. I find that my knees translate anteriorly the most when I do bilateral, barbell back squats. Having the weight across the back forces the torso to lean forward, and I find that it is more difficult to "sit back" and lead with the hips in this set-up. Not surprisingly, I feel this variation the most in my left knee and rarely perform it. Front squats on the other hand, have offered me little pain and discomfort. With the weight positioned across my anterior deltoids and clavicle it is easier to "sit back" to counter the front-loaded position of the weight. Coincidentally, one study has shown that the front squat may be less stressful on the tibiofemoral joint than traditional back squats.
I also employ front grips when performing stationary split squats and rear foot elevated split squats. I have found the least discomfort with these exercises. I also makes sure that I use a long step so that the tibia remains vertical throughout the exercise and I can really 'sit back'. The trade off with a longer stride compared to a shorter stride is less more glute/hamstring activity than solely quadriceps. However, I feel a strong contraction in my quadriceps from using this method and always feel it there the next day. Ultimately anything involving knee flexion and extension will activate the quadriceps to some degree. Of course, to be less stressful to the knee and focus solely on the quadriceps while limiting glute involvement one can always reduce the ROM to a 45 - 60 degree angle of knee flexion. The final video below is of a rear foot elevated barbell split squat. I have been using these more and more lately and have really come to enjoy them. My knee has had no complaints, either.
References:
1.) Fry AC, Smith JC, Schilling BK. Effect of knee position on hip and knee torques
during the barbell squat. Journal of Strength and Conditioining Research. 2003;17(4):629-633.
Interestingly, another study by Escamilla et al. also found that a one-legged squat produced less patellofemoral compressive forces than a bilateral squat with the participant's back supported by the wall with both a short and long step (5). This was counter to their hypothesis that the one-legged squat would have the highest compressive forces. It is worth noting though that in all studies with bilateral squatting a greater load was used in comparison to unilateral exercises.
So What?
Hopefully it appears that both exercises can generate increased strength in the lower extremity.
I have employed both unilateral and bilateral versions in my workouts since coming back to the gym after dislocating my knee cap in 2006 and undergoing surgery to realign the patella and clean out the torn pieces of articular cartilage and bone that was sheared off during the injury.
Not surprisingly, I am very cautious when it comes to my lower body workouts now, and I "listen" to my knees. I find that my knees translate anteriorly the most when I do bilateral, barbell back squats. Having the weight across the back forces the torso to lean forward, and I find that it is more difficult to "sit back" and lead with the hips in this set-up. Not surprisingly, I feel this variation the most in my left knee and rarely perform it. Front squats on the other hand, have offered me little pain and discomfort. With the weight positioned across my anterior deltoids and clavicle it is easier to "sit back" to counter the front-loaded position of the weight. Coincidentally, one study has shown that the front squat may be less stressful on the tibiofemoral joint than traditional back squats.
I also employ front grips when performing stationary split squats and rear foot elevated split squats. I have found the least discomfort with these exercises. I also makes sure that I use a long step so that the tibia remains vertical throughout the exercise and I can really 'sit back'. The trade off with a longer stride compared to a shorter stride is less more glute/hamstring activity than solely quadriceps. However, I feel a strong contraction in my quadriceps from using this method and always feel it there the next day. Ultimately anything involving knee flexion and extension will activate the quadriceps to some degree. Of course, to be less stressful to the knee and focus solely on the quadriceps while limiting glute involvement one can always reduce the ROM to a 45 - 60 degree angle of knee flexion. The final video below is of a rear foot elevated barbell split squat. I have been using these more and more lately and have really come to enjoy them. My knee has had no complaints, either.
References:
1.) Fry AC, Smith JC, Schilling BK. Effect of knee position on hip and knee torques
during the barbell squat. Journal of Strength and Conditioining Research. 2003;17(4):629-633.
2.) Escamilla RF, Fleisig GS, Zheng N, et al. Effects of technique variations on knee biomechanics during the squat and leg press. Medicine & Science in Sports & Exercise. 2001:1552-1566.
3.) "Biomechanics of Patellofemoral Rehabilitation". MikeReinhold.org. http://www.mikereinold.com/2009/06/biomechanics-of-patellofemoral.html. Retrieved May 25, 2012.
4.) Escamilla RF, Zheng N, Macleod T.D., et al. Patellofemoral joint force and stress between a short and long-step forward lunge. Journal of Orthopedic and Sports Physical Therapy. 2008;38(11):681-690.
5.) Escamilla RF, Zheng N, Macleod TD, Edwards BW, Imamura R, Hreljac A, Fleisig GS, Wilk KE, Moorman CT, Andrews JR. Patellofemoral Joint Force and Stress during the Wall Squat and One-Leg Squat. Medicine & Science in Sports & Exercise. 2009; 41 (4): 879-890.
Subscribe to:
Posts (Atom)