Electromyographic Analysis of the Lower Extremity during Pedaling*

Transcription

1 /81 / $02.00/0 THE JOURNAL OF ORTHOPAED~C AND SPORTS PHYSICAL THERAPY Copyright O 1981 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association Electromyographic Analysis of the Lower Extremity during Pedaling* THOMAS M. MOHR,? MS, PT, JOHN D. ALLISON,t MS, PT, ROBERT PATTERSON, PhDt Copyright All rights reserved. EMG activity in the gluteus maximus, rectus femoris, biceps femoris, vastus lateralis, gastrocnemius, and anterior tibialis muscles was studied in six healthy male subjects. Each subject pedaled against changes in workload, pedaling rates, and different weight flywheels, with and without toe clips and from both sitting and standing positions. All the muscles tested were shown to be active at workloads greater than 300 kilograms per minute. In addition, the amplitude of the EMG signals increased with increasing workloads. No real differences in muscle activity timing were found between the light and heavy flywheels or between the competitive and noncompetitive cyclists. Standing while pedaling produced increased activity in the rectus femoris and vastus lateralis at high rpm and low workloads. Bicycle exercises are widely used by physicians for exercise testing and prescription, by physical therapists for lower extremity rehabilitation exercises, and by the general public as a means of obtaining regular exercise to maintain fitness. The purpose of this study was to describe the muscle activity in six lower extremity muscles while pedaling on a bicycle ergometer under various conditions. The subjects pedaled with changes in load, pedaling rates, and flywheel weights, with and without toe clips and in both standing and sitting positions. REVIEW OF LITERATURE Despite widespread use of the bicycle, few studies have reported the EMG activity in the lower extremity while pedaling. Houtz and Fi~cher,~ using surface electrodes, monitored EMG activity in 14 muscles of the trunk and lower extremity during pedaling on a stationary bicycle. They found the most essential muscles ' This work was supported, in part, by Social and Rehabilitation Service Research and Training Grant 16-P t From the Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, MN. Mr. Mohr, who was a graduate student in Physical Therapy at the University of Minnesota when the study was conducted, is now an Instructor in the Physical Therapy Department, University of North Dakota, Grand Forks. ND. for pedaling to be the tensor fascia latae, sartorius, quadriceps femoris, and tibialis anterior. Only minimal activity was present in the gluteus maximus, gluteus medius, sacrospinalis, and rectus abdominis. EMG activity was intensified with either an increase in workload or pedaling rate; however, the timing of the muscles remained orderly and coordinated. Goto et al.' used surface electrodes to monitor the integrated EMG activity in the gluteus maximus, vastus lateralis, gastrocnemius, and the tibilialis anterior muscles. Of subjects who pedaled with increasing workloads and pedaling rates, they found a linear relationship between integrated EMG, pedaling rate, and the workload in the vastus lateralis and gastrocnemius, while the gluteus maximus and tibialis anterior showed curvilinear relationships. Tate and Shierman7 studied EMG activity in the biceps femoris, rectus femoris, gastrocnemius, and tibialis anterior while pedaling with and without toe clips. All the muscles worked for a longer duration throughout the pedal cycle with toe clips than without. METHOD subjects Six healthy male volunteer subjects Were used Mr. Allison is an Associate Professor and Director of the Course in in this study. l-heir ages ranged from Physical Therapy. University of Minnesota. Mr. Patterson is an Assistant Professor and Director of Research, University of Minnesota. years. All were experienced in bicycling. Three

2 164 MOHR ET AL JOSPT Vol. 2. No. 4 Copyright All rights reserved. TABLE 1 Characteristics of subjects Subject Height Weight Age (cm) (kg) (yr) Number of hr biked/wk of the subjects rode bicycles occasionally, one subject was active in recreational biking (subject 2), and two were competitive cyclists (subjects 4 and 6). Anthropometric data and the number of hours biked per week for each subject are given in Table 1. Instrumentation All tests were performed on an electrically braked bicycle ergometer (Quinton model 870; Quinton Instruments, Seattle, WA). The ergometer was modified to accept either a light, spoked flywheel (1.6 kilograms) or a heavy, solid flywheel (36.3 kilograms). The ergometer was calibrated prior to each testing session and again after the flywheels were changed. The pedaling rate was determined by a tachometer built into the bicycle ergometer and was recorded on a chart recorder. Pedal position was indicated on the chart recorder each time the pedal passed 0" (the fully down position) by mechanically tripping a microswitch connected in series to a 1.5- volt dry cell. The original pedals were replaced by pedals to which toe clips could be attached. The toe clips were attached to the pedals, and the pedals were simply turned over when the subject pedaled without them. To record the EMG activity, two surface electrodes were positioned over each muscle studied. The electrodes were 17-millimeter-diameter silver-silver chloride cup electrodes (Beckman Instruments, Inc., Schiller Park, IL). The electrodes were filled with electrode cream and attached to the skin by means of double adhesive tape rings. One large (5- x 1 0-cm) ground plate was used as a central ground lead for all the channels. The EMG signals were amplified by six differential amplifiers (Tektronix 2A61; Tektronix, Inc., Beaverton, OR). The sensitivity was adjusted for each amplifier to give signals which were of sufficient amplitude so that the sequence and duration of the muscle activity could be easily determined. The amplified EMG signals were recorded on an oscillograph chart recorder (model 1200 oscillograph; Midwestern Instruments, Inc., Tulsa, OK) utilizing eight galvonometers. In addition to the six channels of muscle activity, the pedaling rate (rpm) and the pedal position were also recorded on the paper. The EMG signals were also displayed on a cathode ray oscilloscope. Procedure Each subject was given a brief orientation session to familiarize him with the equipment and the protocol to be used during the testing session. The heads of the metatarsals were placed directly over the pedal axis. With the pedal in the fully down position (0") and the ankle in a neutral position, the seat height was adjusted so that the knee was in 30" of flexion. The subject was then instructed to grasp the handle bars, keeping the elbows fully extended. The handle bar height was then adjusted so that each subject's trunk was flexed 20". All the joint measurements were made with a standard goniometer. The six muscles monitored in this study were: 1) the gluteus maximus, 2) the biceps femoris (long head), 3) the rectus femoris, 4) the vastus lateralis, 5) the gastrocnemius, and 6) the tibialis anterior. These muscles were considered representative of the major muscles used during pedaling.3s All the EMG recordings were taken from the right lower extremity. In preliminary studies, it was found that muscle activity patterns in the semimembranosus and semitendinosus were similar to the biceps femoris. Because of a limited number of EMG channels available, only the biceps femoris was used. Preliminary studies also showed similar patterns in both the vastus medialis and vastus lateralis with the latter being chosen for inclusion in this study. The motor point for each muscle was located using a small low volt stimulator. The skin was prepared by shaving the area, abrading the skin with fine sandpaper, and then wiping the area with alcohol. The electrodes were placed approximately 1 centimeter apart and equidistant from the motor point. The ground lead was placed over the right iliac crest on all the subjects. The subject was then told to pedal for 5 seconds at 60 rpm with the load set at 600 kilograms

3 JOSPT Spring EMG OF THE LC IWER EXTREMITY 165 Copyright All rights reserved. per minute. A recording was made, and the sensitivity of each EMG amplifier was adjusted so that signals of sufficient amplitude were recorded to facilitate interpretation of the muscle activity. The same procedure was carried out at 1200 kilograms per minute. If the recordings were of good quality, the testing procedure was begun. In the first part of the test, the subject pedaled at 60 rprn under each of the following workloads: 1) 0,2) 300,3) 600, and 4) 1200 kilograms per minute. The subject pedaled for 30 seconds at each workload, with an EMG recording being made during the last 5 seconds. A 5-minute rest period followed the entire series of loads, during which the subject remained seated on the bicycle. For the second part of the test, the subject pedaled under a load of 300 kilograms per minute at each of the following pedaling rates: 1) 40, 2) 60, 3j 80, and 4) 100 rpm. Again, the subject pedaled for 30 seconds at each rate, and recordings were taken the last 5 seconds. Another 5-minute rest followed completion of this series of pedaling rates. Toe clips were provided for the test's third portion, and the subject was instructed to place his forefoot into the toe clip. The toe clip straps were tightened to hold the foot in place. The subject then pedaled for 30 seconds at 60 rprn with loads of 300 and 600 kilograms per minute. The subject also pedaled at 80 and 100 rprn under a load of 300 kilograms per minute. The three loads and the three pedaling rates were chosen so that comparisons could be made with pedaling without toe clips. As before, the subject rested for 5 minutes following the 2-minute exercise bout. For the last portion of the test, the toe clips were removed, and the subject was instructed to stand on the bicycle and pedal. Each subject pedaled for 30 seconds at 60 rprn with loads of 600 and 1200 kilograms per minute and with a load of 300 kilograms per minute at 40 and 80 rpm. All tests were first done with the heavy flywheel. After installing the light flywheel, the bicycle ergometer was recalibrated, and the entire testing procedure was repeated. None of the subjects reported any subjective feelings of fatigue during or after the testing session. After all the data were collected, the EMG's were analyzed. The duration of activity in this study was determined to be from the time the EMG signal broke the baseline (minimal activity) until the signal returned to the baseline. The EMG signals recorded at workloads of 0 and 300 kilograms per minute were of very low amplitude, making accurate interpretation of the duration data impractical. Poor speed control at 40 rprn and movement artifacts at 100 rprn also made accurate interpretation of this data difficult. For these reasons, muscle activity duration data from the loads of 0 and 300 kilograms per minute and the pedaling rates of 40 and 100 rprn were not reported. RESULTS Figure 1A shows that the portion of the pedal cycle from " produced activity in most of the muscles. During that quadrant of the cycle, the gluteus maximus, biceps femoris, rectus femoris, vastus lateralis, and gastrocnemius were active and apparently working as synergists. The biceps femoris was active from ", but the activity occurring after 0" (360") was only minimal in all the subjects. Although the rectus femoris and the vastus lateralis had similar patterns of activity, the rectus femoris came in earlier in the cycle than the vastus lateralis in all the subjects. The prolonged electrical activity (past 0") in the gastrocnemius was similar to that observed in the biceps femoris. The biceps femoris and the gastrocnemius were the only two muscles active at the bottom of the pedal cycle (0"). The tibialis anterior was the only muscle studied which had all of its activity occurring before 180". The amplitude of the EMG signals increased progressively with the load in all the muscles studied. At 0 kilograms per minute, the gluteus maximus was not active in four of the subjects, but it became active at all other loads in all of the subjects. All the other muscles were generally active at 0 kilograms per minute, usually with only minimal activity. At workloads of 300 kilograms per minute or larger, all the muscles became active. Overall, the EMG signal amplitude changes with increasing pedaling rates were quite variable among the subjects. With increasing pedaling rates, the signal amplitude in some muscles increased, while other muscles showed a resultant decrease in signal amplitude. The velocity signal showed that the speed with the heavy flywheel remained quite constant regardless of the rpm, but the speed with the light

4 MOHR ET AL JOSPT Vol. 2, No. 4 ELECTROMYOGRAPHY OF LOWER EXTREMITY Copyright All rights reserved. Gluteus maximus --.,-' - T-- Biceps femoris o" Rectus femoris - 7- I oo Vastus lateralis Gastrocnemius Tibialis anterior Fig 1 Schemat~c drawing of pedal cycle at a workload of 600 k~lograms per minute at 60 rpm wlth heavy flywheel. (Note that figure was constructed usrng mean duration data) flywheel fluctuated in a sinusoidal fashion. All the subjects experienced difficulty in controlling the speed with the light flywheel. At heavy workloads (1 200 kilograms per minute) and increased pedaling rates (80 and 100 rpm), the speed with the light flywheel became more constant. Very little difference in muscle activity duration was noted between the light and heavy flywheels in the sitting position. The intraindividual differences between the two flywheels were only slight. The amplitude of the signals during sitting with any given load and rpm were similar whether a light or heavy flywheel was used. Figure 1 shows the muscle activity duration patterns while pedaling with and without toe clips. With exception of the rectus femoris and tibialis anterior, only slight differences were seen when toe clips were used. With toe clips, the rectus femoris became active an average of 20" earlier in the pedal cycle. The tibialis anterior, however, came in an average of 27" later in the pedal cycle and had a slightly shorter duration of activity when toe clips were used. The amplitudes of the EMG signals at any given workload and pedaling rate were similar with and without toe clips in all the subjects. Figure 2 compares the duration of activity

5 JOSPT Spring EMG OF THE LOWER EXTREMITY ELECTROMYOGRAPHY OF LOWER EXTREMITY Copyright All rights reserved. Gluteus maximus 1 Biceps femoris o0 Rectus femoris I m0 o0,' 2+,y\:F?!$.;n Vastus lateralis.,. Gastrocnemius Tibialis anterior Fig. 2. Schematic drawing of pedal cycle at a workload of 1200 kilogram per minute at 60 rpm with heavy flywheel. (Note that figure was constructed using mean duration data). during standing and sitting. Although the sequence of muscle activity was similar in both instances, the biceps femoris and gastrocnemius had shorter activity durations during standing, while the gluteus maximus, rectus femoris, and vastus lateralis had longer activity durations. Figure 3 shows the difference in electrical activity occurring between the standing and sitting positions. All the subjects showed a similar increase in signal amplitude of the rectus femoris and vastus lateralis during standing. With a workload of 300 kilograms per minute, the electrical activity in the rectus femoris and vastus lateralis during standing was continuous throughout the pedal cycle. This continuous activity was also observed at 40 rpm but was the most marked at 80 rpm. At 1200 kilograms per minute, the electrical activity in the rectus femoris and vastus lateralis during standing was no longer continuous. While amplitude changes occurred with changes in load and pedaling rate, the timing of the muscles showed little change. For any given subject, the sequence and duration of muscle

6 Gluteus Maximus - Biceps Femoris Rectus Femoris Vastus Lateralis MOHR ET AL JOSPT Vol. 2, No. 4-1 second ELECTROMYOGRAPHY OF LOWER EXTREMITY +? Gastrocnemius Copyright All rights reserved. Tibialis Anterior Cycle marker pulse Velocity - 60 rpm 80 rpm -I 1200 kgmlmin 1200 kgmlmin 300 kgmlmin 300 kgmlmin (standing) (sitting) (standina) (sittina) Fig. 3. EMG tracings from subject 5 showing changes in electrical activity during standing and sitting on the ergometer. Note the volume conduction from the gastrocnemius occurring on the tibialis anterior trace. activity remained quite constant with changes in load, rpm, toe clips, and flywheels. Standing did, however, produce some changes in muscle activity patterns. In addition, the results revealed little difference between the competitive and noncompetitive cyclists. DISCUSSION The biceps femoris and the gluteus maximus showed activity during the pedal downstroke ( ') and apparently work together to extend the hip. The biceps femoris continued to show activity until approximately 55'. This action probably pulls the pedal around at the bottom of the pedal cycle by flexing the leg. The rectus femoris was active earlier in the pedal cycle than the vastus lateralis in all of the subjects. This earlier activity in the rectus femoris could be attributed to its hip flexor action during the pedal upstroke (0-180') or to the initiation of leg extension. Wheatley and Jahnke8 also observed this earlier activity in the rectus femoris during leg extension. Houtz and Fi~cher,~ however, did not find this earlier activity in the rectus femoris but instead found it to work simultaneously with the vastus lateralis during pedaling. In the present study, the activity durations of the gastrocnemius and biceps femoris were similar. The gastrocnemius evidently assists the biceps femoris in pulling the pedal around at the bottom of the cycle. The tibialis anterior was active during the pedal upstroke and apparently dorsiflexes the foot during that portion of the cycle. Houtz and Fischer3 proposed that it may also turn the pedal to a level position in preparation for the extensor thrust of the extremity. The present study showed the rectus femoris, vastus lateralis, biceps femoris, gluteus maximus, and gastrocnemius working together to extend the entire lower extremity during the pedal downstroke. Houtz and Fischer3 did not observe the quadriceps, biceps femoris, and gastrocnemius showing activity concurrently as did the present study. Instead, they found only the rectus femoris, vastus lateralis, and tibialis anterior to be active during the top half of the cycle (90-270"). In addition, they found activity in the biceps femoris and gastrocnemius only during the bottom half of the pedal cycle (270-90').

7 JOSPT Spring EMG OF THE L( IWER EXTREMITY 169 Copyright All rights reserved. Tate and Shierman's finding^,^ similar to the present study, showed the rectus femoris and biceps femoris working together, but they found the gastrocnemius active only from ". Other studies have observed an increase in signal amplitude with both increasing workloads and pedaling rates.', In the present study, the amplitude increased along with the increases in workloads for all the subjects, but the increase in amplitude with increasing pedaling rates was quite variable. The difficulty in controlling the speed of the light flywheel at low rpm and heavier workloads appears to be consistent with other studies. Seabury et a/.= found that, the greater the workload, the higher is the most efficient (as measured by less energy expenditure) pedaling frequency. Other studies have shown that pedaling rate is negatively related to the Borg perceived exertion rating scale especially at lower r ~ m. ~ Tate and Shierman7 found that the use of toe clips elicited a longer duration of activity in the tibialis anterior, rectus femoris, biceps femoris, and gastrocnemius muscles during pedaling. They suggested that the toe clips allowed the subject to "pull up" on the pedal during the pedal upstroke. Another study, which measured crank force, found no evidence of pulling up on the pedals with the use of toe clips by an experienced ~yclist.~ The present study was unable to duplicate the increase in muscle activity duration with toe clips in any of the muscles except the rectus femoris. The rectus femoris showed activity an average of 20" sooner with toe clips. The toe clips may have enabled the rectus femoris to exert an upward force on the pedals as a hip flexor to assist the contralateral leg in rotation of the flywheel. Pedaling from a standing position produced the most marked changes in electrical activity. All the subjects showed continuous activity in the rectus femoris and vastus lateralis during standing with light workloads (300 kilograms per minute). Apparently, the rectus femoris and vastus lateralis must maintain knee extension during the entire pedal cycle (with light loads); thus, they show continuous activity. At heavier workloads (1200 kilograms per minute), these two muscles no longer show continuous activity. Perhaps, at heavier workloads, there is enough pedal resistance so that one can shift the body weight abruptly from side to side. This shift in body weight over the pedaling leg would utilize the body weight to aid in rotation of the flywheel. The weight shift would also take the body weight off the nonpedaling leg. This would allow the rectus femoris and vastus lateralis in the nonpedaling leg to relax and cease electrical activity for the portion of the pedal cycle when the pedaling leg is pushing down. At light workloads (300 kilograms per minute; 80 rpm), this abrupt weight shift is not possible because the pedals offer very little resistance to support the body weight. With the subject standing, the biceps femoris no longer appears to pull the pedal around at the bottom of the pedal cycle as it does in sitting. Again, this might be due to weight shifting during standing. By shifting the body weight from side to side to help rotate the flywheel, the biceps femoris may not be needed to pull the pedal around. The amplitude of the rectus femoris and vastus lateralis signals increased in all the subjects during standing with both heavy and light workloads. This increase in the electrical activity with standing cannot be totally explained by this study, and its investigation in future studies seems warranted. Since standing appears to require more muscle activity, a comparison of oxygen consumption between standing and sitting on the bicycle ergometer would be particularly interesting. From the results of this study, it seems reasonable to conclude that the bicycle offers an excellent means of exercise for all the muscles studied. At workloads of kilograms per minute, all the muscles studied were active. The apparent difficulty in controlling the speed of the light flywheel would suggest that a spoked wheel e'rgometer may not be the best choice when buying equipment for clinical or home use. Although the spoked wheel ergometers are usually cheaper, the poor speed control and difficulty in pedaling at higher workloads may make a closely controlled exercise program difficult to regulate. The spoked wheel ergometers may not be as "comfortable" for the patient to ride; thus, it may discourage a patient from following a prescribed exercise program. SUMMARY The purpose of this study was to investigate the EMG activity in the gluteus maximus, rectus femoris, biceps femoris, vastus lateralis, gastrocnemius, and tibialis anterior during pedaling on a bicyle ergometer.

8 170 MOHR ET AL JOSPT Vol. 2, No. 4 Copyright All rights reserved. Surface electrodes were used to record the activity in six male subjects. The subjects were asked to pedal the ergometer against the following: 1) changes in workload and pedal rates, 2) different weight flywheels, 3) with and without toe clips, and 4) from both sitting and standing positions. The EMG records were analyzed to determine when the muscles were active and the duration of the activity. The results showed that all the muscles are active at loads greater than 300 kilograms per minute and that, aside from interindividual differences, none of the variables changed the timing of the muscles to any great extent. The amplitude of the EMG signals increased progressively with increasing workloads, but the change in EMG amplitude with increasing pedaling rates was quite variable. The light flywheel speed was difficult to control for all of the subjects, but other than that no real differences in muscle activity were found between the light and heavy weight flywheels under any of the conditions studied. Standing produced increased activity in the rectus femoris and vastus lateralis, especially at high rpm and low workloads. Lastly, no apparent difference was found in muscle activity between the competitive and noncompetitive cyclists studied. The authors conclude that all the muscles studied are used during pedaling and that the bicycle would seem to be a good therapeutic tool for exercising the muscles of the lower extremity. The authors wish to thank Helen Skowlund for her help in preparation of this manuscript. REFERENCES 1. Goto S. Toyoshima S, Hoshikawa T: Study of the integrated EMG of leg muscles during pedaling at various loads, frequency, and equivalent power. In: Komi PV (ed), Biomechanics V, Vol A, pp Baltimore: University Park Press Hoes MJAJM. Binkhorst RA, Smeekes-Kuyl AEMC, Vissers ACA: Measurement of forces exerted on pedal and crank during work on a bicycle ergometer at difficult loads. Int Z Angew Physiol Einschl Arbeitsphysiol 26:33-42, Houtz SJ, Fischer FJ: An analysis of muscle action and joint excursion during exercise on a stationary bicycle. J Bone Joint Surg 41-A: , Lollgen H, Ulmer HV. Gross R, Wilbert G, Nieding G: Methodical aspects of perceived exertion rating and its relation to pedaling rate and rotating mass. Eur J Appl Physiol 34: , Pandolf KB, Noble BJ: The effects of pedaling speed and resistance changes on perceived exertion for equivalent power outputs on the bicycle ergometer. Med Sci Sports 5: , Seabury JJ, Adams WC. Ramey MR: Influence of pedaling rate and power output on energy expenditure during bicycle ergometry. Ergonomics 20: , Tate J, Shierman G: Toe clips: how they increase pedaling efficiency. Bicycling 1857, Wheatley JJ. Adams WD: EMG study of the superficial thigh and hip muscles in normal individuals. Arch Phys Med Rehabil 32: , 1951