If you see the patient standing next to you in the pool wearing electrodes and hooked to a computer, don't panic. They are probably participating in one of several research projects currently looking at the use of surface electromyography (SEMG) in the water.
SEMG and Leg Squats
According to Ron Fuller, PTA, ATC, who has co-authored a paper on the use of SEMG in the water, there is a lot of new interest in the idea. "I've even been contacted by an international biofeedback association. Everyone seems interested in what we are doing."
Fuller, along with Kipp Dye, MS, PT, Nancy Cook, PhD, and Brian Awbrey, MD, used surface EMG to assess muscle activity during single leg squats on land and at varied water depths.1 Their research hypothesis states that closed chain exercises performed at varied water depths would produce graded muscle recruitment of the quadriceps muscles.
The study results show that there is a significant difference in the muscle activity of the vastus medialis obliques (VMO) during squats performed on land, in waist-deep, and in chest-deep water. The deeper the water, the less active the muscle. Land-based squats produce the most muscle activity of all three positions.
Clinically, these results make sense. It would seem plausible that a muscle which is required to support a greater body weight (squatting on land) should be more active than a muscle which is only required to support a portion of that body weight (squatting in a buoyant environment).
The clinician should be cautioned, however, to refrain from making any conclusions about the amount of force generated by the quadriceps during these trials. SEMG values are not a direct representation of muscle force, and can only be used to determine electrical activity of a muscle (see "Limitations" sidebar for more details). 2,3
SEMG and Prone Arm Exercises
In another study, SEMG was used to quantify the muscle activity during water shoulder exercises.4 In this study, EMG was used to examine activity of the serratus anterior (a scapular stabilizer) during several prone arm exercises commonly used in rehabilitation of the shoulder.
Subjects performed the same movement patterns at the same velocity of movement first on land (on a plinth) and then in the water (on a specially constructed water plinth). When subjects exercised on land, they lifted a weight against gravity. When subjects exercised in water, they used resistance gloves and bells.
Researchers found that for the movements and velocities tested, the serratus anterior was equally active during prone arm raises using a 2.5 lb. weight (on land) and prone arm raises using a webbed resistance glove (in water).
Additionally, the muscle activity present during prone arm raises with a 5 lb. weight on land were statistically equivalent to the activity present during arm raises using a Hydrotone bell in water.
Finally, muscle activity was less during use of 2.5 lb. weight than a 5 lb. weight, and during use of a webbed glove than a Hydrotone bell (as common sense would suggest).
Why Use SEMG in the Water at All?
Clinicians have very few methods to quantify the effect of resistance exercises performed in the water. It is exceedingly difficult to measure actual resistance to movement in water as resistance can be altered subtly by so many factors. The speed of movement, length of lever arm, exposed frontal surface area, and buoyancy and streamlining of the object can all alter the amount of resistance generated.
Traditional performance measures (goniometry, Manual Muscle Testing, gait assessment, etc.) assessed while submerged in the water fail to provide the clinician with usable data for precisely the reason clinicians use the aquatic environment for rehabilitation: Immersion in water assists function.
So instead, most aquatic studies use subjective Rating of Perceived Exertion (RPE) scales, self-report functional scales, or land based impairment and outcome measurements to quantify the effects of exercise in water. It becomes necessary then to find a performance instrument which is clinically viable on land and remains valid when used in the water. A tool that may lend itself to such a task is surface electromyography (SEMG).
SIDEBAR: Procedures for Use of SEMG in Water
1. Swab subjects skin with an alcohol soaked gauze pad prior to EMG electrode placement. Allow at least one minute allotted for drying.5
2. Place self-adhesive electrode on the selected muscle electrode site as described by Bajmajian.
3 Confirm muscle placement by muscle palpation during a manual muscle test as described by Kendall.6
3. Cover electrode with a bio-occlusive, water-resistant dressing to prevent splash or immersion interference.
4. Attach leads to the subject with waterproof tape to prevent artifact due to unnecessary lead movement. Dab petroleum jelly at the exit port for the lead from under the water-resistant dressing.
5. Secure surface EMG unit poolside.
6. Perform the following EMG normalization procedure (normalization is required to make comparisons between inter-subject electrical activity). The subject stands on land and performs a Manual Muscle Test as described by Kendall.
6 This value is considered 100% muscle activity for the subject. Read peak EMG activity from the unit and document. Observe activity during the trial visually for artifact spikes and if present, repeat normalization trial (normalization values are inadequate if they represent artifact). The data establishes reliability and provides a signal normalization baseline.
7. Take a resting reading of muscle activity to allow discrimination between muscle activity due to exercise movement and muscle activity due to positioning.
8. Perform selected movement pattern at a preselected speed with a pacing metronome (velocity must remain constant throughout trial as muscle activity appears to be altered by changes in velocity).
9. At the end of the experiment, assessed electrode for presence of moisture and a perform a second resting position muscle activity assessment and normalization test (Manual Muscle Test) to rule out the possibility of moisture-based error.
10. Remember, overall, SEMG contamination can be reduced by careful consistent skin preparation, prevention of unnecessary lead movement, shortening leads, using a pre-amplifier at the electrode site, grounding the subject, and choosing a bipolar recording technique.7,8
SIDEBAR: Limitations with Use of SEMG in the Water 5
1. SEMG can only be used to examine superficial muscle groups and represents the gross function of a muscle.2,3
2. Raw SEMG data must be normalized before making intermuscle and intersubject comparisons due to the natural variability of electrical activity between individuals.2
3. SEMG may not represent the true muscle activity unless noise, artifacts, and crosstalk are minimized.2,7,8 SEMG may record any electrical activity near or beneath the electrode, even the electrical activity of the heart.10
4. SEMG values are not a direct representation of muscle force, and can only be used to determine electrical activity of a muscle.2,3 Also, because of changes in muscle length, type of contraction, electrode movement, and changes in the lever arm at a joint, the EMG-force relationship is not linear.2,3 There still exists, therefore, a need to create a relationship between muscle activity (as measured by EMG) and muscle force (as measured by force plates or an isokinetic device).
REFERENCES
1. Awbrey, B., Fuller, R., Dye, K., Cook, N. EMG biofeedback of the VMO using single-leg minisquats at varying depths of water. (1997). Concord, NH: Concord Orthopedics. (Study pending publication).
2. Soderberg, G.L., Cook, T.M. (1984). Electromyography in biomechanics. Phys Ther, 64(12):1813-1820.
3. Basmajian, J.V., DeLuca, C.J. (1995). Muscles alive. 5th ed. Baltimore, MD.: Williams & Wilkins.
4. Becker, K.M., Erlandson, M.O., Hemmesch, R.A., Redfield, D.S. (1996). A comparison of serratus anterior muscle activity during prone exercise in water and on land as measured by a clinical EMG unit. St. Paul, MN: College of St. Catherine. (Unpublished Master's Thesis).
5. Poteat, A.L., Redfield, D.S., Erlandson, M.O., Becker, K.M., Hemmesch, R.A. (1996). Quantification of aquatic physical therapy water-based methods: Part I: Surface electromyography. J Aquatic Phys Ther, 4(1): 13-17.
6. Kendall, F.P., McCreary, E.K., Provance, P.G. (1993). Muscles testing and function. 4th ed. Baltimore, MD: Williams & Wilkins; 288-289.
7. Preece, A.W., Wilmalaratna, H.S., Green, J.L., Churchill, E., Morgan, H.M. (1994). Electromyogr Clin Neurophysiol, 34(2): 81-86.
8. Turker, K.S. (1993). Electromyography: some methodology problems and issues. Phys Ther, 73(10): 698-710.
10. Pink M. (January, 1996). Personal communication with Andrea Poteat.
Disclaimer
The information presented in this article is meant to be a summary and educational in nature. It is not meant to serve as a substitute for legal advice.
Author Bio
Andrea Poteat Salzman, MS, PT is the owner of two businesses, the Aquatic Resources Network and Concepts in Physical Therapy. She has received both the prestiguous Aquatic Therapy Professional of the Year Award (Aquatic Therapy and Rehabilitation Institute) and the Tsunami Aquatic Therapy Award.
Salzman is well-regarded within the industry as:
- Editor-in-Chief of an aquatic therapy trade journal and newsletter;
- Author of over a dozen publications, including the soon-to-be-released Evidence-Based Aquatic Therapy textbook;
- Freelance author and columnist;
- Aquatic therapy seminar instructor;
- Adjunct faculty and research advisor, St. Catherine Physical Therapy Program, Minneapolis, MN;
- Immediate past manager of therapeutic aquatics, St. Paul Ramsey Medical Center, St. Paul, MN;
- Researcher and grant recipient examining aquatic exercise vs. land-based exercise.
She may be reached via e-mail at asalzman@aquaticnet.com
