The Importance of Isometrics

An isometric contraction is a static form of exercise in which a muscle contracts to produce force without an appreciable change in muscle length and without visible joint movement1 We learn these basic concepts in school and are told to provide these types of interventions during the early phases of rehabilitation, but do we truly understand the benefit of these seemingly simple exercises?

Eccentrics versus Isometrics

While eccentric exercise is the mainstay of most rehabilitation programs for tendinopathies, some patients find them painful to complete and difficult to perform.2 In these cases, patient compliance suffers due to increased pain, leading to underwhelming outcomes.3

Conversely, the impact of isometric contraction on pressure pain thresholds (PPTs) yields promising results. When asymptomatic volunteers held a quadriceps isometric contraction at 21% MVIC until exhaustion (maximum of 5-minute duration), patients demonstrated a significant increase in PPT at the start of contraction. PPT continued to increase until the middle of the contraction period and stayed increased for up to 5 minutes post-intervention.4

Reduced Perceived Pain

In a similar study, PPTs were determined after 14 healthy women completed 2 sets of submaximal (40-50% MVIC) isometric exercise consisting of squeezing a dynamometer for 2 minutes with their dominant hand.5 This trial demonstrated a positive contralateral and ipsilateral hypoalgesic effect with elevated PPTs and a reduction in self-perceived pain rating for both hands following isometric exercise. While this provides a good foundation of support, it does not provide information regarding isometric exercise’s effect on individuals with a painful condition

To answer this question, Rio and associates performed a randomized cross-over study to investigate the hypoalgesic impact of a single bout of isometric contractions on individuals with patellar tendinopathy.6 Those in the intervention group performed 5 sets of 45 second isometric quadriceps contractions (70% MVIC) with a 2 minute rest break between each set. Those in the control group performed 4 sets of 8 repetitions (100% 8-repition maximum) of an isotonic leg extension exercise with a 4 second eccentric phase and 3 second concentric phase.

At the conclusion of the study, isometric contractions reduced pain during single-leg decline squat from 7.0 to 0.17 on an 11-point scale and increased MVIC by 18%. Both values were maintained for 45 minutes post-intervention. Also, cortical inhibition increased from 27.5% to 54.9%, which may factor into the underlying mechanism of this hypoalgesia.7

Further supporting the hypoalgesic properties of isometric contractions, Rio and colleagues once again added to the depth of literature in this area. They used a within-session randomized controlled trial to compare isometric leg extension at 60 degrees of knee flexion to isotonic leg extension in volleyball or basketball players with patellar tendinopathy. At the conclusion of the study, those randomized to the isometric knee extension group demonstrated significantly greater immediate analgesia throughout the 4 weeks trial.8

Back to the Basics

Isometrics are not simply an introductory exercise for patients following a post-operative procedure (i.e. quad sets following ACL reconstruction). Their hypoalgesic effects are far more impactful then most of us recognize. Although we are not sure why isometrics are efficacious in these tendinopathies, they give us an intervention that is successful.  Clinicians often get too caught up in complex and intricate treatment philosophies when in reality all we have to do is go back to the basics!

References

1. Kisner, Carolyn, and Lynn Allen. Colby. Therapeutic Exercise: Foundations and Techniques. 5th ed. Philadelphia: F.A. Davis, 2007. Print.

2. Alfredson H, Pietila T, Jonsson P, et al. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med 1998;26:360–6.

3. Visnes H, Hoksrud A, Cook J, et al. No effect of eccentric training on jumper’s knee in volleyball players during the competitive season: a randomized clinical trial. Clin J Sport Med 2005;15:227–34.

4. Kosek E, Ekholm J. Modulation of pressure pain thresholds during and following isometric contraction. Pain 1995;61:481–6.

5. Koltyn KF, Umeda M. Contralateral attenuation of pain after short-duration submaximal isometric exercise. J Pain 2007;8:887–92.

6. Rio E, Kidgell D, Purdam C, et al. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. British Journal of Sports Medicine. 2015;49(19):1277-1283. doi:10.1136/bjsports-2014-094386.

7. Rio E, Kidgell D, Moseley GL, et al. Tendon neuroplastic training: changing the way we think about tendon rehabilitation: a narrative review. British Journal of Sports Medicine.2015.

8. Rio E, van Ark M, Docking S, Moseley GL, Dawson K, Gaida J, van den Akker-Scheek I, Zwerver J, Cook J. Isometric Contractions Are More Analgesic Than Isotonic Contractions for Patellar Tendon Pain: An In-Season Randomized Clinical Trial. Clinical Journal of Sport Medicine. 2016.

Evidence-Based Strength Training: Gluteus Maximus

To build upon my previous post regarding Evidence-based Strength Training of the Gluteus Medius, I wrote the following article for MedBridge Education

Pain and Gluteal Strength

The gluteal musculature has been implicated in many different pathologies due to its potential impact on lower extremity biomechanics. During weight bearing, the femur moves about a fixed patella and therefore excessive femoral internal rotation and adduction results in increased contact directed primarily at the lateral facet of the patella1. Just 10° of IR can lead to a substantial decrease in PFJ contract area and a 50% increase in joint stress. Coinciding with these findings, Souza et al.2 found that females with patellofemoral pain syndrome (PFPS) demonstrated greater peak hip internal rotation compared to the control group during running, drop jump, and step down. The PFPS group also demonstrated 14% weaker hip abductor strength and 17% weaker hip extensor strength. Wilson et al3, Noehren et al4, and Nakagawa et al5 found that individuals presenting with PFPS demonstrated increased hip adduction during running, jumping, and single-leg squats. This excess femoral adduction creates an increased valgus force about the knee joint, which in turn causes increased loading of the lateral patellofemoral joint. In addition to patellofemoral pain, a hip etiology or influence has also been implicated in iliotibial band syndrome6, anterior cruciate ligament rupture7, and achilles tendinopathy8. More specifically, impaired gluteus maximus function has been demonstrated in individuals diagnosed with femoroacetabular impingement9.

Gluteal strengthening and Rehabilitation

In support of a gluteal etiology, several studies have found the effectiveness of gluteal strengthening in the treatment of lower extremity disorders. A recent systematic review conducted by Santos and colleagues9 found gluteal strengthening decreased the highest intensity of pain experienced during the previous week, pain when ascending and descending stairs, and pain while squatting or sitting for prolonged periods amongst individuals diagnosed with PFPS. Additionally, with regards to rehabilitation following anterior cruciate ligament reconstruction, the inclusion of hip strengthening appears to improve sagittal plane dynamic balance at three months post ACLR as compared to traditional rehabilitation10.

EMG Activity and Exercise Goals

According to Reiman et al.11 and Escamilla et al.12, moderate electromyographic activity (EMG) activation (21-40% MVIC) is best used to facilitate endurance and neuromuscular re-education; high activation (41-60+% MVIC) in order to promote strength gains.

From Biomechanics to Exercises

Gluteus Maximus

Origin: Ilium posterior to posterior gluteal line; dorsal surface of sacrum and coccyx; sacrotuberous ligament

Insertion: Iliotibial tract and gluteal tuberosity

Primary Function: Extends thigh and assists in hip abduction and external rotation; steadies thigh and assists in rising from sitting position

Among introductory exercises, the gluteus maximus achieves the highest EMG levels during:

  1. Front-plank with Hip Extension
  2. Gluteal Squeeze
  3. Side-plank with Hip Abduction
  4. Quadruped with Contralateral Arm/Leg Lift
  5. Uni-lateral Bridge

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Additionally, you must consider the interaction of other muscles acting with or against the gluteus maximus when determining exercise prescription. It has been proposed that individuals who demonstrate excess femoral internal rotation during functional tasks may be relying too heavily on the tensor fasciae latae to control their pelvis in the presence of weak or inhibited gluteus medius musculature.

Selkowitz and colleagues determined that the following exercises achieved the best Gluteal to Tensor Fasciae Latae Activation Ratio:

  1. Clamshell
  2. Side-step with resistance band
  3. Single-leg bridge
  4. Quadruped hip extension with knee extended
  5. Quadruped hip extension with knee flexed

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Finally, when progressing your patient towards more functional closed kinetic chain and sport/activity-specific exercises, the following exercises achieve the highest gluteus medius activation:

  1. Cross-over Step-up
  2. Hip Thrust Variations (Barbell, Band, American)
  3. Rotational Single-Leg Squat
  4. Skater Squat
  5. Single-Leg Squat

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Exercise prescription is a multi-faceted decision, which is driven by the individual patient’s goals, functional limitations, and the evidence supporting the treatment of these factors. Using EMG studies to drive the selection of exercise is highly valuable, especially during early stages of rehabilitation or when attempting to isolate individual muscles and/or groups of muscles. However, there are limitations when comparing different studies due to methodological differences (type of EMG, patient population, data analysis, etc.). Additionally, due to the cost and time to conduct these studies, there are thousands of exercises that have not been evaluated in the literature. In light of this information, these studies should be used to guide your decision making, it should not override your clinical expertise when accompanied by biological plausibility.

Evidence-Based Strength Training: Scapulothoracic Musculature, Part 1

In the next installment of the Evidence-Based Strength Training Series for MedBridge Education, we are going to take a look at the often-neglected scapulothoracic musculature. Typically when considering the management of painful upper quarter conditions, local exercise and manual therapy interventions are employed judiciously. However, when utilizing a proper movement assessment or regional interdependence philosophy, impairments in the scapulothoracic musculature are often found to contribute to pain in distal or proximal joints. Weakness or diminished neuromuscular control of the peri-scapular muscles has been implicated in Subacromial Impingement4,18, Lateral Epicondylalgia2,7,12, Cervicogenic Headache10, and Neck Pain3,16. Additionally, in a prospective cohort study conducted by Clarsen et al.6, the presence of scapular dyskinesis led to an 8.4x greater risk for developing a shoulder injury during the course of an elite male handball season. Furthering the support for interventions focusing on the peri-scapular musculature, Lawrence and colleagues11 found that in the presence of shoulder pain due to subacromial impingement, patients demonstrated significantly reduced scapulothoracic upward rotation at lower angles of humerothoracic elevation and significantly reduced sternoclavicular posterior rotation throughout humerothoracic elevation.

With the knowledge of the scapulothoracic musculature’s impact on potentially injurious altered biomechanics and the deficits seen in many common musculoskeletal disorders, healthcare providers need to ask themselves, “What are the best exercises to recruit these muscles?”

Before delving into specific exercises, it is necessary to understand the basic biomechanics of the scapulothoracic and glenohumeral joints. During humeral elevation, the scapula upwardly rotates 1° for every 2° of humeral elevation until 120° humeral elevation is achieved. After this point, scapular rotation contributes 1° for every 1° humeral elevation until maximal arm elevation is met. Also, the scapula typically tilts posteriorly between 20° and 40° in the sagittal plane and externally rotates between 15° and 35° in the transverse plane17. This complex movement pattern relies on coordinated and balanced contributions from the trapezius, serratus anterior, levator scapulae, rhomboid, and pectoralis minor musculature.

Trapezius Musculature

The broad posterior musculature known as the trapezius originates at the medial third of superior nuchal line, external occipital protuberance, nuchal ligament, and the spinous processes of C7-T12 vertebrae and its distal insertion is at the lateral third of clavicle, acromion process, and spine of scapula. This muscle is divided into three distinct portions with the Upper Trapezius (UT) providing scapular elevation, Lower Trapezius (LT) proving depression, and the Middle Trapezius (MT) causing scapular retraction. Additionally, the UT and LT act together to rotate the glenoid cavity superiorly, which is a very important and often dysfunctional action for individuals suffering from shoulder impingement or pain11.

The primary action of the upper trapezius musculature involves elevation of the scapula and, predictably, the exercises that provide the highest Maximal Isometric Voluntary Contraction (MVIC) are those that involve this motion. Additionally, during scapular abduction, upper trapezius activity progressively increases from 0° to 60° and from 120° to 180° of abduction1. With this knowledge in mind, researchers have found that the highest electromyographical (EMG) activity occurs during the uni-lateral shoulder shrug9, rowing14, scaption8, and shoulder abduction in the scapular plane above 120°9. Due to the infrequency of UT weakness (unless secondary to neurological involvement) strengthening of this portion of the trapezius is often not the focus during the rehabilitation of painful upper quarter conditions. Instead, clinicians have learned to focus on improving middle and lower trapezius strength and normalizing the ratio of UT to the lower two portions of the trapezius activation.

[Table] Click to see MVIC values for UT exercises

Similar to the UT, the middle trapezius, with its primary function being scapular retraction, is often activated during exercises involving this action. The highest MVIC percentages for the MT have been recorded during horizontal abduction14, prone full-can9, horizontal abduction with external rotation14, and scaption8. Additionally, as the UT often compensates for a weak MT or lower trapezius, it is likely beneficial to utilize exercises with a good upper trapezius to middle trapezius ratio (UT:MT) when attempting to strengthen this musculature. Exercises shown to provide this ratio are side-lying forward flexion, side-lying external rotation, and prone shoulder extension5.

[Table] Click to see MVIC values for MT exercises

 

Due to its impact on scapular upward rotation, external rotation, and posterior tilt, the lower trapezius is of more importance than the aforementioned UT and MT during rehabilitation17. There have been a multitude of studies investigating lower trapezius weakness and its association with painful conditions and most do find this connection. Due to this fact, there have also been many studies looking into maximal EMG activity of the lower trapezius during upper extremity strengthening. The results show that significantly high MVIC values have been recorded during arm raise overhead in line with the LT muscle fibers9, ER at 90° of abduction9,15, horizontal abduction with ER5, and prone shoulder abduction5. While choosing exercises with a relatively high MVIC is important, it may be more important to choose those exercises that provide an optimal upper trapezius to lower trapezius ratio (UT:LT). As these are the two primary muscle groups involved in upward rotation of the scapula, having adequate and relatively equal contributions from each is important in maintaining normal biomechanics. In a study conducted by Cools and colleagues, it was determined that side-lying forward flexion, side-lying external rotation, and horizontal abduction with external rotation had the best UT:LT ratios5. In addition to this study, McCabe et al. conducted a similar study and found that the seated press-up, uni-lateral scapular retraction, and bilateral shoulder external rotation provided UT:LT ratios that showed a preferential activation of the lower trapezius over the upper trapezius13. While these studies do give a glimpse into proper exercise selection, not every exercise has been studied to date and never will. When choosing an exercise for your patient/client, it is important to take into consideration the biomechanics of the movement, current evidence supporting/refuting, and your patient’s presentation and goals for treatment.

[Table] Click to see MVIC values for LT exercises

 

The trapezius musculature is a very important piece of the puzzle, but contributions from the Serratus Anterior, Rhomboids, and Levator Scapulae also play a large role and will be discussed in Part 2.