Squat, Press, Extend or Flex for Strong Legs & Healthy Knees, Pt. 5

In the previous installment of this series, we looked at Closed Kinetic Chain Exercises and some of their applications. In this installment, we will look at Open Kinetic Chain Exercises and how they can be used safely and effectively.


Open Kinetic Chain Exercises

Leg Extension: The first OKCE to highlight is the leg extension. In fact, some of the reasons why this article was written was in part due to the overwhelming amount of questions I’ve personally addressed over the last 18 months during seminars and workshops all over the world. The leg extension has been used for many years by everyone from a bodybuilders to a physical therapists, for the purposes of strengthening the quadriceps muscle. Nevertheless, the biomechanics of this movement on this type of machine places unnecessary stress on the anterior part of the knee. This is because the loading is perpendicular to the long axis of the tibia. As the joint moves upon contraction of the quadriceps, “shear force” is created which places the knee joint in a compromising position for optimum safety. During the performance of a leg extension the quadriceps reacts by pulling the tibia forward, while simultaneously the ACL opposes this action by trying to prevent the translation of the tibia. This phenomenon called tibial translation places a huge amount of stress on the ACL and therefore something to give specific thought to.

Primarily there are different types of forces applied to the knee joint when considering the choice between CKCE’s and OKCE’s. The forces applied to the knee during a squat are termed “compressive forces” which are the forces that a joint can handle and accommodate more safely than the counterpart “shear forces”, as described in the explanation above.

Leg Curl: The second OKCE is the leg curl. Such as in the leg extension, many will argue against the “functionality” of this movement because of the single joint action, which only allows the hamstring to function as a knee flexor. The question then becomes “what is functional”? If the hamstrings are both knee flexors and hip extensors, then what is the proper way to train them and does training them in only one fashion or the other have any implications with knee safety and the ultimate goal of stronger legs?

As of the writing of this article on behalf of myself with over 30 years of industry experience, many of my peers, or in any published clinical journals have I been able to conclude that there are many if at all any significant contraindications with the proper use of the leg curl as I have been able to find with the leg extension through research and personal experience. So, my position with the leg curl is to use it wisely with controlled, non-ballistic movements. Is it functional? Yes, it is. Other than resorting to some of the many new modalities of exercising in today’s market such as stability balls, suspension exercise, bands, cables, etc., the leg curl machine allows us to perform under such a position.

There has been a surge over the last 10 or so years on the whole “functional” exercise option being more important for the athlete and client than traditional weight lifting because of the whole body integration that occurs in most “functional” based programs. This is where the experience of the fitness professional and CEC’s have such a huge impact! Functionality and functional abilities can be broken up into six major and absolutely essential factors. Perhaps the most forgotten one is muscular strength. Needless to say, both the leg extension and the leg curl will increase muscular strength to a degree–something to consider when all else that is better for the knee has been attempted without avail. This would be reference to the older, severely deconditioned adult, handicapped individual or a recent rehabilitation patient trying to gain range of motion.

In a classic research study by Fiatarone in 1990, it was demonstrated that the functional scores on walking and balance tests improved by 48% and lower body strength increased by 175% when following an 8 week regimen of training 3 days a week performing 3 sets of 8 repetitions. Nevertheless, the average age of the participants was 90! So what was the risk to benefit ratio? It was obviously in favor of the benefit.

Although we know that shear forces are great when performing leg extension compared to squats, leg presses and lunges, in the case of the study group mentioned above, we can assess that a properly performed squat, leg press or lunge may not be possible for many in that age group. Or, perhaps the movements would have been possible, but the minimal rep performance and lack of form would have had little to no positive adaptations.

We’re back to identifying that in reality there is NO WRONG exercise or movement but rather WRONG applications of the exercises or movement in question. The purpose of this article is to have a good look at all the options available, identify the positives and negatives from the inside out and then apply the correct exercise at the proper time based on your client’s needs and overall bigger picture.


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5. Mechanics of human joints: Physiology, Pathophysiology, and treatment. Unsworth, A. 1993

6. Basic Orthopaedic Biomechanics, Second Edition, Van C. Mow, Wilson C. Haynes, 1997

7. Medial Collateral Ligament Tears, Cedars-Sinai, 2012, a 501(c)(3)

8. Arthroscopic repair of traumatic longitudinal meniscal tears, K Roeddecker, G.D. Giebel, C. Lohscheidt and M. Nagelschmidt, 1993, Vol 7 Num 1

9. Meniscus tear recovery time, Benjamin Wedro, MD, FACEP, FAAEM, 2012

10. Bursitis, The Basics, What you should know about bursitis, 2012 Carol Eustice, ASCP, ARHP

About the Author

Felix Doval is the founder and owner of Pro-Active Wellness, a leading South Florida Health and Fitness education provider whose curriculums are taught using the private training facilities of Active Bodyz Fitness Training located in Davie, FL. Felix holds a Master Certification with the NFPT, and is NSCA and NAHF certified.

He is a graduate of a two year Natural Health Consultant program at Stratford Career Institute in Washington DC, and from the Professional Career Development Institutes’ Professional Fitness and Nutrition program in Atlanta, GA. His advanced knowledge includes multiple specialty studies in the fields of diabetes, heart disease, arthritis, lung disease, and osteoporosis.

He has directed and developed wellness programs around the nation and is currently responsible for developing, staffing and coordinating the NFPTs’ worldwide workshop division.


These resources are for the purpose of personal trainer growth and development through Continuing Education which advances the knowledge of fitness professionals. This article is written for NFPT Certified Personal Trainers to receive Continuing Education Credit (CEC). Please contact NFPT at 800.729.6378 or [email protected] with questions or for more information.
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