Comparison of Shoulder ER/IR and Flexion/ Extension Strength Ratio Using Cybex vs 10-RM with Weighted Pulley

Kelsey Tobin, SPT and Steven Blom, SPT

cybex-vs-10-rm

14 Comments on “Comparison of Shoulder ER/IR and Flexion/ Extension Strength Ratio Using Cybex vs 10-RM with Weighted Pulley

  1. In your exclusion criteria for subjects, people were excluded if they had impingement-like symptoms. How was impingement-like symptoms defined? Did you guys perform a subjective history of impingement-like symptoms, perform any special tests like Hawkins-Kennedy or painful arc before having subjects perform this testing? Also do you think the reported discomfort with flexion on the pulley system was from impingement or anything else specific? Thank you!

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    • Great questions, Spencer. We did not actually test for shoulder impingement but had a question regarding the diagnosis on our intake questionnaire form (amongst other questions to rule out shoulder pathology), so we just attained this information subjectively. We also did not include a definitive definition for this particular diagnosis which may have provided more clarification as to what we were looking for. We chose to include “impingement-like” symptoms as an exclusion criteria because this is a very common finding in the general population, highly due to our lifestyle, always being in a poor forward-flexed posture, narrowing that subacromial space and causing pain/discomfort, especially with overhead movements. Two of the movements included in our study both contribute to the closing of that subacromial space (flexion, IR), especially if our subjects had a pronated grip rather than a neutral grip on the handle for the isokinetic machine and/or the pulley system, which we did not control for. We found that even if our subjects did not voice having a shoulder pathology on their intake form, two or three of them experienced similar symptoms to shoulder impingement (as described above) when testing shoulder flexion on the pulley system. We did not assess whether or not this was actually shoulder impingement or explore further what was causing their pain, we simply excluded them from our data. I think it could have been in part due to shoulder impingement or due to the fact that we did not have subjects warm up their shoulder prior to 10-RM testing.

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  2. Because the actual 10RM max was found 2 days post isokinetic testing, did you have anyone complaining of delayed onset soreness? Do you think having the testing so close together may have limited the participants ability to give full maximal effort when finding their actual 10RM?

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    • Most of the subjects that we recruited happened to be fairly active already, whether it be from cardiovascular conditioning or weightlifting; however, I do recall a couple of them reporting soreness from the isokinetic unit. I do believe this may have influenced the 10-RM they were able to achieve 2 days following. We definitely could have given subjects one more day in between testing.

      I did also find that since the isokinetic machine fatigued most subjects prior to finding their initial 10-RM on the first testing day, the weight that we had subjects start with for their 10-RM 2 days following typically seemed too light for them so some subjects fatigued rather rather quickly from doing more sets to find their 10-RM. In this case, I think fatigue may have been a more limiting factor than soreness.

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      • Matt, I do believe delayed onset muscle soreness had an effect on our results. Granted a lot of our subjects were fairly active people, but our muscle strength training including some fairly unfamiliar movements patterns. How often does one lie down on their back, fully extend their elbow, and move through flexion/extension and IR/ER movement patterns. I also believe lack of motor control and coordination had an effect because of the unfamiliarity with the movement patterns. Even after the first training day, the subjects were more familiar with the movement patterns and their strength values could have been increased because of this. We know that in strength training, the first changes that occur are mostly neurological rather than physiological changes in muscle fiber composition or mass. Delayed onset muscle soreness may have caused a decrease in strength values, while neurological changes may have caused an increase.

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  3. After knowing what you now know about your study, if you were to repeat the study would there be anything that you would choose to do differently? If yes, what and why?

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    • Alli, Yes I think there are a few things we would do differently. First of all, we would utilize 1 lbs weights instead of 2.5 pound weights to be more precise. If you look at our strength values with the weighted pulley system they go to the nearest 2.5 pounds. Going to the nearest pound would give us a more precise strength value. Second, we only gave our subjects one days rest between the first day of testing and the second. A fair amount of our subjects complained about some muscle soreness from the first day of testing. Although, a lot of our subjects were active and worked out frequently, these movement patterns were relatively unfamiliar to the subjects and muscle soreness resulted. I think giving the subjects 2 or 3 days rest would have decreased the effect of this factor. Third, we could have had stricter requirements on when we would disqualify a subject from achieving their 10 repetition maximum on the weighted pulley machine. With the isokinetic machine there was more stabilization utilized. With the weighted pulley machine we simply used a rolled towel and explained to the subject to avoid compensating. After watching some of the subjects test there strength, it was hard to be consistent when deciding when a patient was compensating too much with shoulder shrugging. We could have used a more consistent system for identifying amount of compensation that was allowed during testing.

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  4. Interesting with the references you chose. I would be interested in looking at multiple speeds of testing with both types of resistance, especially with the age group you selected. I feel this would have been an interesting aspect of the study to include. How did you decide on the speed of testing. What type of activity level where these subjects: athletes, regular exercise, inactive, etc.?

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    • Matt, if you could please reference my reply to Ike below, I discussed how we chose the testing speed for both the Cybex isokinetic unit and the 10RM on the weighted pulley system. To answer your second question, most of the subjects who partook in our study were graduate students from USD. I think the topic of our study was appealing to active individuals – most of these students had been collegiate athletes (softball, cross country, basketball, volleyball, etc.) so were previously very active. Many of these same students now partake in intramurals and/or utilize the wellness center for fitness classes, to do some cardio, and/or to lift weights. I don’t recall any of our subjects being “inactive” – I don’t think inactive students would have wanted to partake in a study that involved lifting weights! Thank you for your questions!

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  5. You discussed finding a correlation between strength values, but not ratios with the Cybex and 10RM. Taking this into the clinical setting would you utilize a weighted pulley system at initial evaluation to assess for overall strength or find an area of deficit and use it as part of an outcome measure? Without ratios, was there any statistically important values for strength that displayed that humeral migration occurs consistently and could potentially lead to injury or has already lead to an injury?

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    • Although we would have loved for our study to prove that we could use a 10 RM to identify strength ratios, the statistics we found proved the exact opposite. There are simply too many factors involved with determining a 10 RM that could prove a patient is at risk for injury. Again, our results only show that you can identify that a patient is making improvements in strength by using a 10 RM on the weighted pulley. The amount of error that was still present after all the steps we took for standardization of muscle strength suggests how difficult it is to identify a ratio. It is eye opening how subject and how much error is involved with the MMT which are so frequently used. You would really need an isokinetic machine to identify a ratio. And even if you do come up with a ratio, there are so many other factors to consider. ROM, patient history with overhead activities, posture, activity level, motor control, and coordination amongst other variable will all have an effect on if a patient is at risk.

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  6. What were the reasons for choosing 6 working reps on the Cybex in a 2 second concentric and 2 second eccentric tempo and then comparing it to a 10 RM? What were the reasons for choosing different rep ranges for the two forms of tests. Also, was tempo controlled in the same manner during the pulley test and if no, why was it not?

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    • In the literature that we referenced prior to initiating our study, the set isokinetic unit speeds that we found had varied between 60 and 300 degrees per second. We chose 90 degrees per second for our own study because this is a more realistic speed that is comparable to lifting weights in the gym (for those of us who lift in a controlled manner). Other that than, there is really no particular reason we went with that speed. We just chose a speed and went with it for the duration of our study. Each repetition utilizing the Cybex was maximum effort, which is why we only chose to have participants perform 6 repetitions. We did not want them to become too fatigued by performing too many repetitions. The point of utilizing the Cybex is to find max torque but we wanted to give subjects more than 1 rep to find that due to unfamiliarity with the machine. Switching over to the chosen 10RM parameters, we found that a 2 second concentric, followed by a 2 second eccentric, phase most closely mimicked the 90 degrees per second set speed on the Cybex. We controlled this for the 10RM through the utilization of a metronome for each subject. We also chose a 10RM because we have found in the literature that for strength gains, you should have patients perform working sets somewhere between 8-12 repetitions of a certain percent of their maximum effort. This is a great parameter for strength gains but also a great working set to compare between various joint motions to assess similarities or differences in strength, as we did for our study. It is not realistic in a clinical setting to test a patient’s 1 RM as this really serves no purpose. You want to find what they are able to perform in 8-12 repetitions (or the 10 that we chose) and modify their weight from there. Again, to reiterate, the main purpose of our study was to show that we can utilize a weighted pulley system in a clinical setting to find similar information as is found in a lab setting for the Cybex when looking at shoulder muscle strength in patients so we are able to address any shoulder muscle imbalances that could potentially lead to injury. Thank you for your question!

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  7. I am curious whether shoulder joint laxity or instability arose as an issue while testing subjects? The position of testing for IR and ER (supine, 90 degrees abduction, 90 degrees elbow flexion) is particularly of interest to me. From a personal standpoint, performing resisted external and internal rotation to a repetition maximum in this position is uncomfortable for me because of a feeling as though my shoulder might “pop out” especially when I am becoming fatigued. As far as I know, I have not had shoulder injuries. Thanks for your feedback!

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