Mind-Muscle Connection, Patellofemoral Pain

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I have heard the phrase “mind-muscle connection” numerous times over the years. Anecdotally, I think we all knew there was something to it. Recently, this paper was published to address the matter a bit more objectively: Differential effects of attentional focus strategies during long-term resistance training.

“Attentional focus can be operationally defined as what an individual thinks about when performing a given activity (Schoenfeld & Contreras, 2016).”

External focus has been well demonstrated to improve performance -oriented tasks; as seen in sport. “A recent review by Wulf (2013) concluded that an external focus showed better improvements in motor learning compared to an internal focus in more than 90% of published studies on the topic.” Practically, you wouldn’t want to focus on a precise muscle, say the subscapularis when you throw a baseball, rather it would be far superior to focus on the desired outcome of the skill itself.

An internal focus, or mind-muscle connection, may be useful for resistance training. This is speculated to be influential for hypertrophy and strength gains since “…electromyographic (EMG) studies report greater EMG amplitudes of the target musculature during resistance exercise with the use of an internal focus (Snyder & Fry, 2012; Snyder & Leech, 2009).” In this case, it would be beneficial to focus on “feeling” the targeted muscle during resistance exercise; example being the subscapularis during a resisted internal rotation.

“Thus, the purpose of this study was to investigate the effects of using an internal versus external focus during RT on muscular adaptations.”

Subjects: “30 male volunteers (age = 21.7 ± 3.7 years; height = 176.3 ± 9.1 cm; mass = 78.2 ± 18.4 kg) recruited from a university population.” Participants were pair-matched based on pre-study muscle thickness, and therefore randomly assigned evenly into internal vs external focus groups. All participants were healthy and drug-free.

Methods: The subjects followed an 8-week resistance training (RT) period, with one week before and after the 8-week program for testing, accumulating 10 weeks total. The RT protocol followed a 3 day/week split, training on nonconsecutive days, utilizing the barbell biceps curl and machine knee extension for 4 sets of 8-12 reps, with 2 minutes rest between sets. Intensity was gauged from 10RM testing.

The internal focus group was instructed to “squeeze the muscle!”

The external group was instructed to “get the weight up!”

Anthropometrical measurements taken included body mass (BM), body composition via InBody BIA, muscle thickness (MT) via ultrasound of the elbow flexors, mid-thigh, and lateral thigh. Isometric knee extension and elbow flexion were also measured before and after the training program.

Results: The elbow flexors of the internal focus group showed significantly greater hypertrophy (p=0.003) compared to the external focus group. No additional outcome measures demonstrated statistical significance or a relevant effect size.

“The differences in changes in elbow flexor size between INTERNAL and EXTERNAL (12.4% vs. 6.9%, respectively) translated into a large magnitude of effect favouring the INTERNAL condition (n2p= 0.307).”

Take-home point: The mind-muscle connection does prove true, as speculated, but more so for the biceps than the quadriceps. It could be speculated that this is a result of the larger motor units in the quadriceps have less fine-motor control when compared to upper extremity muscles that are more often involved with higher-level coordination tasks. That being said, it could be true that a longer training duration may allow for more motor learning to occur, creating a similar adaption for the quadriceps as the biceps.

 

After a recent conversation about PFP, I found a nice write-up reviewing a lot of literature on Patellofemoral Pain in Athletes

Introduction: “Patellofemoral pain (PFP) is the accepted term for localized pain of the anterior aspect of the knee.” This is a very general term and still is not well understood. PFP is commonly seen with anterior loading of the knee, particularly in sports with high volumes of jumping. “In an observational study of 810 adolescent basketball players, the overall prevalence of PFP was 25%, with ~26% of female and 18% of male players affected.” In the same study, PFPS “…was the most common diagnosis with an overall prevalence of 6.4%. Other less common diagnoses included Sinding-Larsen-Johansson disease (4.8%), Osgood Schlatter disease (2.5%), and plica syndrome (2.3%).” PFPS can present with or without structural damage being present.

Pathophysiology: There has been MRI reports that have shown no association between PFPS and structural damage. Another systematic review showed “…an increased MRI bisect offset, increased patellar tilt, and increased congruence angle under load and without load were associated with PFP. All of these imaging parameters are indices of patellar maltracking.” There has since been a number of studies claiming maltracking is thought to be highly correlated to PFPS.

Valgus: The Q-angle and dynamic valgus have been blamed for much of the existing PFP, without strong literature to support such. Despite this, it is widely understood that “an increase in the Q angle increases the lateral force on the patella” which may contribute to patellar instability and PFOA. Literature has also shower higher incidences of PFP and dynamic valgus in females, possibly lending one to consider a correlation.

Muscular Dysfunction: Intra-quadriceps imbalances have shown to be corelative with PFP, particularly the medial musculature compared to the lateral musculature. While some papers point the finger at the weaker medialis compared to lateralis, other reports have showed overall quadriceps strengthening is of greater value then attempting to segregate precise muscles. The same is true to PFOA, since decreased quadriceps size/strength is a known risk factor. When it comes to the hip musculature, “A systematic review demonstrated strong evidence that females with PFP have decreased hip abduction, external rotation, and extension strength compared with healthy controls.” Other reports have victimized the decreased activation of the medial hamstring muscles when compared to healthy control groups.

Foot Disorders: “There is strong evidence that, in some patients, foot disorders or deformities such as increased rearfoot eversion or pes pronatus valgus contribute to functional valgus. This deformity can cause internal rotation of the tibia in patients with PFPS.” Other studies have correlated additional factors such as increased navicular drop, navicular drift, dorsiflexion, and forefoot abduction.

Nonsurgical Treatment Options: “Two recently published articles describe the guidelines for conservative management of PFP: These publications, the “2016 Patellofemoral Pain Consensus Statement” and the “Best Practice Guidelines” both recommended interventions that include exercise, taping, bracing, foot orthoses, and combined therapies. More effective programs include training the hip external rotators, abductors, and knee extensors. Other incidences of decreased pain have been seen from other exercises that target the hip and knee, as well as core musculature. Neuromuscular coordination training in both open and closed chain have shown to be effective also. Additional evidence shows a moderate effect from taping and bracing strategies may be effective to improve patellar tracking. Similar results were seen by patients who were prescribed foot orthotics for their PFP. It is unclear if decreased pain is the result of psychological factors or the equipment itself.

Take-home point: The greatest evidence supports increasing lower extremity strength with exercise, where most studies had a duration of approximately 6 weeks. Also, patellar tracking may increase the incidence of PFP, be it a result of dynamic valgus in a depth-jump or muscular imbalances in vitro.

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Thanks,
AJ

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