Single Leg Strength

So thanks to Covid we’re still in lockdown.  When gyms are going to reopen remains unclear. That means more home workouts. Some of you might be well equipped with adjustable dumbbells, a trap bar and the like. Most of us are rather limited in our equipment choices though. A pull up bar, a sling trainer and maybe a kettlebell or two is is probably the limit of what constitutes a home gym for people who live in a flat. 

For upper body training, that is fine. Pull Ups, single arm push ups, single arm inverted rows and headstand push ups are great compound moves. Incline and decline versions and band resistance/assistance can be used to scale intensity. I know few people – aside from the odd gymnast – who can not make upper body strength gains with calisthenics exercises. 

For lower body exercises, things are unfortunately not that easy. For one, there is an upper limit to intensity. Once an athlete is able to perform single leg squats for reps, there is no way around weights for further progression of intensity. Of course, plyometrics are an option, but they serve a different purpose than the grinding lifts and hence, fall into a different bucket. Another issue with lower body calisthenics is the ease of scalability, or rather the lack thereof. The gap between a reverse lunge and a skater squat is enormous. Of course, the sling trainer and jump stretch bands can be used for a partial deload, but that comes with a host of issues. Fixing a band on the ceiling requires a hook or anchor, which is not necessarily feasible for everyone. The sling trainer can be used for assistance, but it’s rather hard to quantify the level of assistance accurately.

In theory, a spring scale could be attached to the suspension trainer to gauge the magnitude of arm assistance. I have yet to try this, so I might be wrong here, but I believe that this is not particularly feasible in the real world. Reading the scale in real time without a partner is probably rather difficult. Further experimentation is needed on this matter, so I reserve the right to change my mind.

From my observation, athletes tend to alter their movement patterns when they’re performing assisted lower body exercises. From a motor learning point of view, I do not want them to go to positions that compromise balance and are just impossible to hold without the assistance. That’s another reason I prefer to progress the squat pattern via variation of the exercise rather than decrease the amount of assistance over time.

In this article, I try to offer a taxonomy of squat variations that can be used to control the intensity of home workouts. The premise here is that the athlete has access to one, but not necessarily more, weights. I use a kettlebell as an example, but a dumbell, weighted vest or even a bag pack filled with canned food can be used in its stead. 

The exercises considered in this article are the goblet squat, split squat, rear foot elevated split squat, skater squat and pistol squat. All of these can be performed with an additional weight or using bodyweight only. The amount of weight that is put on the working leg is gradually increased in these exercises. Due to the symmetrical stance, the goblet squat places 50% of the weight on each foot. In the split squat, the lead foot accounts for 75% (McCurdy 2017) of vertical force production, in the rear foot elevated split squat (RFESS) this number goes up to 85% (Helme 2020). Obviously, in the skater and pistol squat variations, the whole load is placed on the working leg.

I have calculated the amount of weight that is moved by the working leg for two different models. In both cases, I assumed a bodyweight of 80kg and, where applicable, a 16kg kettlebell. The first model is what I call the naïve model. In this model, I consider the total bodyweight for each exercise. So, for the the goblet squat, I’d take the sum of bodyweight (80kg) and kettlebell weight (16kg) and distribute the result (96kg) evenly across both legs, which produces the amount of weight (48kg) each of them has to move. This model roughly align swith ground reaction forces, but not necessarily joint moments.

Although the skater squat and pistol squat exhibit the same amount of weight per leg, I have ranked the pistol squat as the harder / more intense exercise as it allows for slightly more range of motion (ROM), resulting in more work (F * d) to be performed per repetition. For the sake of argument, I have also included the High Bar Squat with 150% BW as additional weight in the Table. At 100kg per leg is is just slightly more intense than the kettlebell pistol squat. While a 1.5BW squat is far from strong, it may be sufficiently heavy to elicit hypertrophic adaptations.

Exercise	BW	External	Total	Per Leg
Goblet Squat	80	16	96	48
Split Squat	80	0	80	60
RFESS	80	0	80	68
Split Squat	80	16	96	72
Skater Squat	80	0	80	80
Pistol Squat	80	0	80	80
RFESS	80	16	96	81,6
Skater Squat	80	16	96	96
Pistol Squat	80	16	96	96
High Bar Squat	80	120	200	100

The second model is a bit more sophisticated, but still wrong. Here, I calculate the amount of weight to be lifted by considering the weight of the upper body and each leg individually. ExRx.net states that the total leg (thigh, leg and foot) accounts for roughly 16-18% of the total bodyweight. I went with 20%, to make calculations easier (bear in mind there is an implicit error in the model anyway, so 2% of BW in either way will not make or break the taxonomy on a conceptual level). For a squat, where both legs are fixed on the ground, I therefore consider the total load to be 60% of bodyweight plus the weight of the kettlebell. In contrast, in a kettlebell pistol squat, where one leg is completely lifted off the floor, the total load is calculated as 80% bodyweight plus the kettlebell. This yields a slightly different ranking of the considered exercises. While the loaded RFESS was more intense in the naïve model, it is the other way around in the compartmentalized model. I believe this approach to be slightly more suitable for real world application. Again, I have included the 150% BW high bar squat for reference and just like before, it is just slightly more intense than the loaded pistol squat.

Exercise	BW	External	Total	Per Leg
Goblet Squat	80	16	64	32
Split Squat	80	0	48	36
RFESS	80	0	56	47,6
Split Squat	80	16	64	48
RFESS	80	16	64	54,4
Skater Squat	80	0	64	64
Pistol Squat	80	0	64	64
Skater Squat	80	16	80	80
Pistol Squat	80	16	80	80
High Bar Squat	80	120	168	84

Both presented models are gross oversimplifications of a complex movement. Neither of them takes into account moment arms for participating joints, EMG muscle activation patterns (for whatever they’re worth), multiplanar stability issues (e.g., the skater squat inherently has to be harder than the RFESS as the glute med has to stabilize the pelvis in the frontal plane), etc. Hence, take them with a grain of salt. Still, I believe that they’re useful – albeit wrong – for progressing the squat pattern during home training while this lockdown lasts. Whether you prefer to use this for laying out a daily undulating program (DUP) in the Heavy-Medium-Light fashion, or implement something more linear (say, 8-12 reps in the first three weeks, followed by 5-8 and finally, 3-5) is completely up to you. Just don’t skip leg day.

As always, I’d love to hear your thoughts on the topic. If this is helpful to you, let me know. Even if it is not, feel free to offer critique. We have a saying in the German language that basically boils down to „talking connects people“. I’m looking forward to an discussion.

So long, don’t get hurt

References

Helme, Mark, Stacey Emmonds, and Chris Low. „Is the Rear Foot Elevated Split Squat Unilateral? An Investigation Into the Kinetic and Kinematic Demands.“ Journal of Strength and Conditioning Research (2020).

McCurdy, Kevin. „Technique, Variation, and Progression of the Rear-Foot-Elevated Split Squat.“ Strength & Conditioning Journal 39.6 (2017): 93-97.