I often get asked something along the lines of: “Shall I do a bicep curl or dumbbell curl?”…”Are squats and deadlifts enough to strengthen the lower body?”… “ I don’t enjoy dumbbell exercises because I can’t go heavy, can I just do barbell exercises instead?”

In this article, I want to try and provide a brief look at some key points as to why both unilateral and bilateral exercises need to be understood, and how they are earnest tools in your arsenal to consider when optimising your training routine.

So what do the terms bilateral and unilateral mean?

Bilateral Training

Bi-lateral training, simply put means that you are working both limbs/sides simultaneously. Both limbs share the resistance and work together to move the load.

So in relation to lower body bilateral movements, these would be exercises such as the two-legged squat and deadlift variations.

In upper body movements these would be exercises like the barbell bench press and barbell row.

Benefits of bilateral training

• Bilateral lifts produce greater force production and power enhancements in trained individuals – The ability to move more weight, at a fast velocity means that force production and power enhancements can be achieved ^[1].

• Heavy loading capabilities – Bilateral exercises have the ability to increase strength quickly through greater total load on the body’s musculature and central nervous system compared to unilateral resistance training alone. Strength based sports and competitions like powerlifting and Olympic weightlifting revolve around big bilateral movements.

• Generally easier exercises to perform – Bilateral exercises may be the better choice for those lacking confidence or experience to help build a base level of competence before progressing onto more difficult unilateral exercises. Bilateral exercises require less mental concentration and body awareness to maintain good.

• High level of skill and strength transfer from bilateral to unilateral exercises - Trained individuals who are strong in a bilateral lifts, such as the barbell chest press tend to have a good strength transfer to the unilateral variation, like the single-arm dumbbell chest press in a relatively short amount of time.

• Reduced injury risk when performing explosive exercises – Explosive bilateral exercises are considered less risky to perform than the precarious positioning required for unilateral movements.

• Can’t beat a ‘Classic’ – The bilateral lifts have been a staple lift in exercise programming for generations of fitness professionals and practitioners, helping develop some of the most aspiring physiques and physical capabilities we have ever seen, so something must be working.

Unilateral Training

Uni-lateral training refers to working one limb/side of the body at a time.

Lower body unilateral exercises are exercises where the majority of the load is placed on leg at a time, even though both legs can be in contact with the ground – such as the lunge, step up, split squat variations, and single leg deadlift variations.

Upper body unilateral movements refer to exercises that involve moving your arms separately from each other, these would be exercises such as the single-arm dumbbell chest press, and single-arm bent over dumbbell rows.

Benefits of unilateral training

• Activation of the body’s stabilisers – To combat rotational forces and unwanted movement, and to maintain quality form, requires the use of the body’s stabiliser muscles ^{[2, 3]}.

• Unilateral training has been shown to have a crossover effect – This means that when you’re working one side, the other side is also affected to a minor extent ^[4].

• Used to great effect in rehabilitation programs to help stimulate the muscle in the untrained limb – With the crossover affect, there will not be as great a strength loss in the injured muscle, which will result in quicker recovery time to previous strength levels ^{[4, 5]}.

• Research suggests that unilateral training can help reduce the bilateral deficit – The bilateral deficit simply refers to when the sum of the maximum weight lifted by both limbs in a unilateral exercise, for example, the lunge, would be less than the total lifted in a bilateral exercise like the squat. There are many factors to consider here such as biomechanics, training age and stabiliser muscle recruitment. However, the bilateral deficit is very apparent in untrained individuals and can be very beneficial to help fix imbalances ^{[6, 7]}.

• Simulates ‘everyday’ movements – Most movements in everyday life require us to be moving our legs and arms unilaterally, climbing the stairs, walking or running involve the limbs being used separately ^{[8, 9]}. Certainly we should look at strengthening these specific movement patterns, particularly for more senior individuals who want to reduce their risk of falling or losing balance.

• Helps establish a mind muscle or neurological connection – Unilateral exercises can be used to help target and isolate weaker or inactive muscles, like getting the glute medius firing before a squat session with some single leg hip thrusts.

Unilateral training and genetics

If you happen to have a poor lactate clearance and recovery ability based on your training age, MCT and ACTN3 results, you should pay close attention to your bodies response to unilateral training, especially lower body unilateral training. Too much lactate production accompanied with the eccentric loading of an intense lower body unilateral workout could lead to a higher rate of perceived exertion and could even hinder your future training sessions with those dreaded DOM’s following you around for longer than desired.

Although, this does not mean that you should avoid unilateral exercises altogether as there is something very magical about performing exercises unilaterally – mainly the fact you know if you have performed them well for a few days after, mechanical damage at it’s best.

A study by Pescatello et al. suggests that certain genetic variations can be more susceptible to benefitting more from unilateral exercises to others. They found that the ACE ID genotype was associated with the “contralateral muscle strength and size effects of unilateral resistance training” ^[12].

References

1. Hermassi, Souhail, Mohamed Souhaiel Chelly, Zouhair Tabka, Roy J. Shephard, and Karim Chamari. "Effects of 8-week in-season upper and lower limb heavy resistance training on the peak power, throwing velocity, and sprint performance of elite male handball players." The Journal of Strength & Conditioning Research25, no. 9 (2011): 2424-2433
2. Carroll TJ, Herbert RD, Munn J, Lee M, Gandevia S (2006) Contralateral effects of unilateral strength training: evidence and possible mechanisms. J Appl Physiol 101:1514–1522
3. Uh, B.S., Beynnon, B.D., Helie, B.V., Alosa, D.M. and Renstrom, A., 2000. The benefit of a single-leg strength training program for the muscles around the untrained ankle. The American journal of sports medicine, 28(4), pp.568-573.
4. Hale, S.A., Fergus, A., Axmacher, R. and Kiser, K., 2014. Bilateral improvements in lower extremity function after unilateral balance training in individuals with chronic ankle instability. Journal of athletic training, 49(2), pp.181-191.
5. Behm, D.G., Leonard, A.M., Young, W.B., Bonsey, W.A. and MacKinnon, S.N. (2005) Trunk muscle electromyographic activity with unstable and unilateral exercises. Journal of Strength and Conditioning Research. Vol. 19, No. 1: 193-201.
6. Saeterbakken, A. and Fimland, M. (2012) Muscle activity of the core during bilateral, unilateral, seated and standing resistance exercise.. European Journal of Applied Physiology. Vol. 112, No. 5: 1671.
7. Simenz, C., Garceau, L., Lutsch, B. and Suchomel, T. (2012) Electromyographical Analysis of Lower Extremity Muscle Activation During Variations of the Loaded Step-Up Exercise. Journal of Strength and Conditioning Research. Vol. 26, No. 12: 3398-3405.
8. McCurdy, K. Langford, G. Doscher, M. Wiley, L. Mallard, G. (2005). The effects of short-term unilateral and bilateral lower-body resistance training on measures of strength and power. Journal of Strength and Conditioning Research. 19 (1), 9-15.
9. Hoffman, J. (2012) NCSA’s Guide to Programme Design. Champaign: Human Kinetics.
10. Jones , M., Ambegaonkar, J., Nindl, B., Smith, J. and Headley, S. (2012) Effects of unilateral and and bilateral lower body heavy resistance exercise on muscle activity and testosterone responses . The Journal of Strength and Conditioning Research. Vol. 26, No. 4: 1094–1100.
11. Hrysomallis, C., 2009. Hip adductors' strength, flexibility, and injury risk. The Journal of Strength & Conditioning Research, 23(5), pp.1514-1517.
12. Pescatello, L.S., Kostek, M.A., Gordish-Dressman, H.E.A.T.H.E.R., Thompson, P.D., Seip, R.L., Price, T.B., Angelopoulos, T.J., Clarkson, P.M., Gordon, P.M.,

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