A new study just came out in the Journal of Sports Rehabilitation that compared EMG activity of select lower extremity muscles in the performance of a two-leg squat (TLS) and what they called a modified single-leg squat (MSLS). For most of us, we’d call it a Bulgarian split squat or rear foot elevated split squat.
Recently, there’s been some uproar in the strength and conditioning community in regard to some coaches choosing to remove traditional TLS from their programming. While I think there are few if any contraindicated exercises, there are contraindicated people when it comes to certain exercises such as heavy back squats for athletes with back issues or overhead pressing for people with shoulder issues.
So when I saw this study I thought it would be of interest. Keep in mind that this study doesn’t address the issues as to why some coaches have decided to remove heavy TLS from their programs. I also want to note that I’m not interested in starting another debate on whether athletes or general population fitness-enthusiasts should back squat. It is merely a comparison of the TLS and the MSLS in regard to muscle activity. Make your own choices as to what exercises you deem appropriate based on the needs of the individual.
A few things I liked about this study: They used real (female) athletes, they made an effort to keep the kinematics the same for tibial anterior translation and trunk inclincation for each subject, and they used legitimate loading. One of my pet peeves is research that only uses body weight or very light loads for strength training research. In this study they used 85% of a tested 3 rep max for both the TLS and MSLS assuring the same relative intensity.
Something I didn’t like: The MSLS was a new exercise for the athletes. To the researcher’s credit, they did give them practice sessions with supervised instruction to assure accurate exercise performance. Anyone who’s trained for a while knows that you can shift the demands of a squat from a “quad dominant” strategy to a “hip dominant” strategy by shifting the hips posteriorly, increasing trunk inclination, and keeping the tibia more vertical. Farrokhi, et. al. showed that an increased forward lean during a lunge increased the demand on the hip extensors. By making an effort to keep the kinematics the same for each subject from TLS to the MSLS, the researchers minimized this influence of tibia and trunk angle on the muscle activity. One average, the subjects were able to maintain just over 85% of the total system weight (body weight + barbell load) on the front leg.
The Outcome
The MSLS produced increase demands on the gluteus medius and hamstrings and reduced demands on quadriceps, whereas the TLS produce greater demands on the quadriceps with reduced hamstring and gluteus medius activity. There was a significant difference in trunk inclination angle between the TLS and MSLS (TLS inclination was higher), but it didn’t seem to affect the muscle activity.
The researchers also noted an increased valgus angle of the knee during MSLS. This is not an uncommon finding in research involving females and exercises demanding greater stability.
A few thougths…
I don’t think the findings are a big surprise. The MSLS has greater demands on stability compared to the TLS, therefore muscles responsible for stabilizing the hip and knee should show increased activity.
I also don’t think this study is support for the elimination of TLS and/or double leg strength work as the “you play on one leg, so you should train on one leg because it’s more specific” crowd may feel. The reduced quadriceps activity may be indicative of reduced overall force output. High-speed ground-based activities like change of direction require high levels of quadriceps activity. According to Chiu, Garhammer, and Schilling, the TLS was found to be more specific to such activities because of the high force demands. Training solely on a single leg certainly won’t provide for the demands of high force activities.
However, improving stabilizer fatigue resistance may be an important factor in helping to maintain those high force abilities.
So which is better, MSLS or TLS? Neither. We benefit from both two-leg and single-leg exercises strength and power exercises in an effective sports training program.
One other small note to keep in mind. Research only applies to the population examined, so these results may not apply to male subjects.
References:
Journal of Sport Rehabilitation, 2010, 19, 57-70
J Orthop Sports Phys Ther., 2008, July 38(7), 403-9