Quick Hit Summary

Functional movement exercises are the rage these days in performance training and rehab settings. However, the importance of including isolation exercises should not be lost as they too play a vital role in any physical development program. This article will focus on open chain kinetic/isolation movements and their role in physical performance and injury prevention.

Functional vs. Isolation Movements Revisited

Figure 1. Should we be training movements or muscles? Image created by Sean Casey

“Train movements, not muscles” is a mantra that has become ingrained in both performance training and rehabilitation circles in the last 10 to 15 years. Functional, movement specific exercise does play a key role in training and rehabilitation, allowing for the transference of strength to performance. For this reason, closed kinetic chain training (CKC) is extremely beneficial for both competitive and recreational athletes alike. However, many individuals still need isolated, open kinetic chain (OKC) or relatively isolated, muscle specific closed kinetic chain exercise to address deficiencies in strength.

{For reference closed kinetic chain (CKC) exercises are movements in which one’s distal limb (ie- hand, foot) is in a fixed position. An example would be squats or pullups. In contrast, open kinetic chain (OKC) exercises are characterized by one distal limb moving freely during the movement. An example would be a bicep curl, or leg extension.}

A thorough examination of isolated muscle strength will help identify when and where focused strengthening is needed. Deficits in functional stability and strength can be identified utilizing tools such as the Functional Movement Screen. This type of assessment tool will help identify a region or joint of the body where deficiencies in motor control or strength are present. A specific assessment of muscle strength and endurance in the region of the suspected problem can then be completed. It is essential to test the muscles that cross the joint in question as well as those supporting the joint above and below.

An Explanation of How Muscle Activity is Measured in Research Studies

The standard for studying muscle recruitment is electromyography (EMG), which measures the electrical activity of a muscle when it contracts. Higher electrical activity correlates with greater muscle tension. Measurements of EMG activity for a given muscle are recorded during a maximal voluntary isometric contraction (MVIC). In other words, individuals contract the given muscle group as hard as they can while pushing/pulling against an immovable object. An example of this would be measuring the electrical activity of the quadriceps while performing an isometric, max effort, squat. Whatever this value happens to be is considered the standard upon which all other EMG outputs, obtained while doing specific exercises, are compared against.

EMG Activity of Various Muscles during Isolation and Compound Exercises

Figure 1. Variations of the lunge are popular CKC exercises and are an excellent training activity. EMG activity for the quads is 45% of MVC, just over threshold for strengthening EMG for the hip abductors and rotators is 33%, below threshold for strengthening. Image courtesy of author

Figure 2. Side-lying hip abduction targets the gluteus medius. This OKC exercise produces EMG activity at 70-80% of MVC. Be sure that the athlete is going through a full ROM, as weakness in the hip abductors and rotators is frequently a component of injuries in the lower kinetic chain. Image courtesy of author

In studies carried out by Bolgla et al. and by Donatelli, muscle activity of the hip and trunk was assessed by placing surface electrodes over the targeted muscles of the lower quarter. In a group of 16 healthy adults, Bolgla measured electrical activity of the gluteus medius during a MVIC. Subjects then completed isolated exercise in both OKC and CKC conditions¹. Using similar methodology in a group of 19 healthy adults, Donatelli examined electrical activity of the gluteus medius, as well as other hip and core muscles, during 9 core exercises². When results of the studies are compared, EMG activity of the gluteus medius reached 40 to 60% of MVIC during isolated OKC and CKC exercises, while functional exercises such as the lunge, bridge and lateral lunge elicited only 28 to 33% of MVIC¹².

According to Donatelli et al., for strengthening to occur, EMG activity must reach > 40% of MVIC for a given muscle; 20-40% MVIC will improve muscular endurance, and < 20% MVIC will result in neuromuscular re-education, but will not improve endurance or strength². Results of the two studies noted above suggest that only the isolated strengthening exercises would supply a sufficient challenge to the gluteus medius to facilitate gains in muscular strength.

CKC vs. OKC Exercises on Muscle Activity

Activity of the hip abductors and the hip external rotators falls below the 40% of MVIC threshold with most CKC exercises². Furthermore, functional movements such as body weight lunging will elicit EMG activity of about 45% of MVIC in the quads. This is enough to improve muscle strength, but it is still well below the 80-90% MVIC that can be achieved with OKC knee extension¹. In situations where a muscular imbalance is present, closed kinetic chain or integrated exercises can reinforce the imbalance, resulting in strengthening of the muscles already being used to compensate for those that are deficient.

Normal joint mechanics require an appropriate balance in recruitment of both the agonist and the antagonist muscles. If there is an imbalance due to a strength deficit in one or more of the muscles that cross a joint, thus contributing to joint stability and mobility, then a pathologic process can be triggered. Compensatory patterns in muscle or muscle groups often are the precursors to injury.

Application to Training and Rehabilitation

Figures 3 & 4 OKC hip abduction and hip abduction combined with extension (to target the posterior fibers of the glut med as well as the glut max). Both muscular strength and endurance must be addressed in the training or rehabilitation process.

Lower extremity injuries such as patellofemoral stress syndrome, ACL tears and shin splints have been correlated with hip musculature weakness³⁴⁵. The hip abductors and external rotators are the muscles that control transverse (rotational) and frontal plane (front & back) motion of the knee during activities such as landing from a jump or cutting maneuvers³⁴. Exercises that isolate and target the hip rotators and abductors can significantly improve knee mechanics by reducing femoral internal rotation and knee valgus during landing (ie- knee twisting inward or caving in)²³⁵. Functional exercises alone often do not result in resolution of isolated strength deficits.

Problems in the upper extremities can also occur without isolated strength training. The individual muscles of the rotator cuff and the scapular stabilizers must function sufficiently to allow normal scapular and glenohumeral mechanics during overhead athletic movements such as throwing or spiking and serving in volleyball. In the weight room and in the clinic, it is more common to see isolated strengthening of the shoulder musculature than of the lower quarter. The reasoning behind the need for isolated strengthening in the lower quarter applies to the upper quarter. I will address upper quarter issues at another time.

My injury rehabilitation and performance training programs almost always include isolated strengthening. Even in athletes without complaints of pain, I often find significant isolated strength deficits. I contend that some of the athletes that I see in the clinic have injuries that could have been avoided if their training program included examination to identify strength deficits and exercises to address them.

Bottom Line

Ultimately a training or rehabilitation program should return to functional or sport specific exercise, but only after individual muscle strength has been addressed. It is this author’s opinion that any training macrocycle should include some isolated strengthening. This type of exercise can also be included during the competition phase for most sports because of the relatively low load required to achieve muscle fiber recruitment.

In the coming months I will discuss utilizing functional screens and muscle testing to identify strength deficits and present 2 cases that highlight the principal of targeted OKC strength training to address the problems that resulted from isolated strength deficiencies.

References

¹ Bolgla, L. A., Uhl, T.L., Electromyographic Analysis of Hip Rehabilitation Exercises in a Group of Healthy Subjects. J Orthoped Sports Phys Ther 2005; 35(8).

² Donatelli, R.A., Carp, K.C., Ekstrom, R.A. Electromyographic Analysis of Core Trunk, Hip, and Thigh Muscles During 9 Rehabilitation Exercises. J Orthop Sports Phys Ther 2007; 37:12)

³ Foster JB. Patello-Femoral Pain Research Refocuses on Hip Biomechanics. Biomechanics. January 2007. 53-56

⁴ Fukuda, T.Y. et al, Short-term Effects of Hip Abductors and Lateral Rotators Strengthening in Femaleswith Patellofemoral Pain Syndrome: A Randomized Controlled Clinical Trial, J Orthoped Sports Phys Ther 2010;40(11).

⁵ Lowry CD, Cleland JA, Dyke K. Management of patients with patellofemoral pain syndrome using a multimodal approach: a case series. J Orthop Sports Phys Ther 2008; 38(11)