MVCs

[Drew Smith]

Colleagues,

Our research group is investigating muscle activity and 3D motion of circus artists. We have hoping to collect surface EMG data and normalize these data to MVC trials where we attempt to isolate each muscle as much as possible and elicit a maximal contraction. Participants will be asked to provide three MVCs per muscle. The list of muscles is below and we would be very interested if readers might share with us best practices for eliciting good MVCs from these muscles. Some are not too difficult but others, based on the fact we are seeing +200% activity during our targeted maneuvers, suggest to us that we could have done a better job during the MVC trials. Thanks in advance for any insights or suggestions.

MUSCLES: Erector spinae, Latissimus dorsi, Trapezius, Pectoralis major, Biceps brachii, Triceps brachii, Infraspinatus, Rectus abdomius, External obliques, Serratus anterior, and Tensor fascia latae.

[Edmund Cramp]

One factor in getting an MVC level from the subject is the degree to which the subject works at the contractions.
I was told this by the Therapists working in the original Rancho Los Amigos, Los Angeles lab about 40 years ago when I was helping them get their Vicon Motion Capture system up and running ... they told me that when the therapist said "Please perform this leg motion, could you try a little more please? Thank you" they would see an MVC level, but when the therapist started screaming "HARDER HARDER HARDER PUSH AT THIS OR I WILL SHOVE YOU!" then they got a much larger MVC signal than the quieter therapist obtained when their subject was doing the same motion to generate an MVC data collection.
Having written the description above and then thinking about today's social media posting world I would like to say that I was just saying what I was told, it's not a criticism at all - the lab was always very good at collecting data and discussing any potential issues to help resolve them - which resulted in me making a lot of visits. Essentially I think that it was just presented that way to me to help me understand an issue in the data collection and processing during my visit to the lab. It was always a wonderful lab to visit and I completely trusted everything they told me.

[Drew Smith]

Thanks for the reply, Ed. My background includes being in kinesiology/sports science settings and the sort of 'encouragement' you mentioned was something one regularly heard in labs. I find that working with PTs/physios, they are less inclined to 'scream' at participants, although I do think it does elicit stronger contractions. We are considering some kind of visual feedback: e.g., EMGWorks can display a vertical bar showing the relative amplitude of the recorded signal.

But our interest also includes hearing how readers may have had success in the actual mechanics of getting some of those muscles fully activated in addition to your suggestion on 'motivation', i.e., positioning of the participant and investigator.

[Edmund Cramp]

You might want to try audio feedback - connecting the EMG channel to an audio amplifier would mean that the subject could hear the contraction without having to try and maintain a posture allowing them to see it.