Electroencephalography and Clinical Neurophysiology , 1979, 47:571--581 © Elsevier/North-Holland Scientific Publishers, Ltd.
571
PERIOD-AMPLITUDE ANALYSIS O F EMG FROM SLOW AND FAST EXTENSORS OF CAT D U R I N G LOCOMOTION AND JUMPING B. BETTS and J.L. SMITH
Neuromuscular Research Laboratory and Brain Research Institute, University o f California, Los Angeles, Calif. 90024 (U.S.A.)
(Accepted for publication: March 1, 1979)
Motor units can be separated into slow and fast contracting populations on the basis of their twitch contraction times (Wuerker et al. 1965; Mosher et al. 1972; Burke et al. 1973; Proske and Waite 1974). Most limb muscles are composed of a mixture of slow and fast units; however, in cats, extensor synergists such as the triceps surae (McPhedran et al. 1965; Ariano et al. 1973; Burke et al. 1974; Hammarberg 1974) and triceps brachii (Collatos et al. 1977} include one or more heads that are composed predominantly or totally of slow contracting units and one or more that are primarily composed of fast units. In studying the recruitment of fast and slow synergists at the ankle during unrestrained movements in cats, both Smith et al. (1977) and Walmsley et al. (1978) found that the peak of the rectified-averaged electromyogram (A-EMG) for the fast muscle closely reflected the kinetic demands of the movements, while the slow muscle showed a steady EMG level which was more independent of the m o v e m e n t kinetics. Although the peak of the A-EMG quantifies overall activity of the muscle, it provides no information a b o u t the frequency and amplitude distribution of the signal. Therefore, we sought a more detailed analysis for the raw EMG. In the past, raw EMG has been analyzed during normal movements (Grieve and Cavanagh 1973; Visser and de Rijke 1975; Komi and Viitasalo 1976) and in the diagnosis of myopathies using period analytic techniques (Willison 1964; Dowling et al. 1968;
Fusfeld 1971, 1972; Hirose and Sobue 1972}, while spectral analysis has been used in the detection of fatigue states (Sato 1965; Kadefors et al. 1968; Ortengren et al. 1975). Spectral analysis provides a description of the distribution of the total average power in a signal as a function of frequency (Ortengren 1975). Period analysis is based on the temporal distribution of 'critical points', specifically zero crossings of the signal or its first two derivatives, and the determination of the statistical distribution of those points; one of the most c o m m o n being mean zero crossing rate (Saltzberg 1973). Some of the analyses include amplitude measures (Willison 1964; Dowling et al. 1968; Hirose and Sobue 1972; Grieve and Cavanagh 1973; Komi and Viitasalo 1976}; however, none describes the two~iimensional period-amplitude distribution of the EMG, although interval-amplitude and period-amplitude analytic techniques have been recently applied to EEG (Leader et al. 1967; Legewie and Probst 1969; R~mond 1975; Harner and Ostergren 1976; Harner 1977). We have developed a real-time periodamplitude analysis program for EMG which is unique in that it stores events two-dimensionally, with coordinates given by the period and amplitude difference between maxima and minima. In addition, periods between zero crossings of the original signal are stored. In this way, most of the information in the raw EMG is retained in an easily interpreted form. We have found this technique of EMG analy-
B. BETTS, J.L. SMITH
572
sis useful in differentiating the activity patterns of slow and fast extensors at the elbow, which have not been previously studied, and at the ankle during unrestrained movements in cats. Preliminary results have been reported previously (Betts et al. 1977). ANO Methods
Data acquisition The lateral gastrocnemius (LG) and soleus (SOL) of the hind limb and the lateral head of the triceps brachii (LT) and anconeus (ANC) of the forelimb in five adult, female cats, weighing 2.3--3.3 kg, were chronically implanted under sodium pentobarbital using a technique described previously (Betts et al. 1976}. The implant, capable of 4 bipolar recordings, consisted of 8 electrode wires, made from multistranded stainless steel wire (Bergen microlin No. 9.6) with an outside diameter of 0.28 mm, 4 encased in each of two Silastic tubes and led from a head connector to the muscles to be implanted. In some of the forelimb implants, a smaller electrode wire (Bergen microlin No. 3.9) with an outside diameter of 0.2 mm was used. Each electrode, with 1 mm of insulation scraped, was threaded through a 22-gauge needle which had been passed through the muscle and was later removed leaving the exposed portion of the electrode embedded in the muscle. The pair of electrodes were placed within 1--2 mm of each other and sutured at their point of exit from the muscle. Both slow extensors, ANC and SOL, are composed totally of slow-twitch oxidative fibers, or type SO (Burke et al. 1974; Collatos et al. 1977}, while the fast extensors, LT and LG, are mixed muscles composed of 75--85% fasttwitch fibers with a higher percentage of fasttwitch glycolytic (FG} fibers than fast-twitch oxidative-glycolytic (FOG) fibers (Ariano et al. 1973; Collatos et al. 1977). During the recording sessions, a PAM-FM four-channel telemetry transmitter having a volume of 125 cu. cm (Biodata Systems, Los Angeles) was
]~mV 500 ms
Fig. 1. Typical telemetered electromyograms during an 80 cm jump to a platform recorded from lateral triceps (LT) anconeus (ANC), lateral gastrocnemius (LG) and soteus (SOL).
connected to the cat's skull plug for transmission of the myopotentials. The telemetry has a frequency response of 20--1000 c/sec and resulted in EMG recordings with a noise level of 150 pV p-p. Electromyograms, which were all full interference patterns as shown in Figure 1, were recorded on FM tape and a video system was used to synchronize the cat's movements with the associated EMG as described earlier (Betts et al. 1976). A BCD code, which changed every 2 sec, was used to synchronize all records. The cats were trained with food rewards to perform vertical jumps to a platform placed at 30--90 cm above the floor and run on a treadmill at speeds of 0.7--2.0 m/sec. Steps and jumps to be analyzed were selected by viewing the video record and choosing bursts of EMG which were artefact-free and related to normal steps during which the cat remained in a relatively fixed position on the treadmill, or
P E R I O D - A M P L I T U D E A N A L Y S I S OF SLOW AND F A S T EMG
period and amplitude constitutes an event, and events from one or more contractions of a single muscle were stored in a frequencyamplitude table (Fig. 2C). For example, the event in Fig. 2A is tabulated at a point corresponding to its computed amplitude of 2.2 mV and period of 5.0 msec (25 samples at 5000 samples per sec), which is expressed as a frequency of 200 c/sec (Fig. 2C). By converting computed periods and amplitudes immediately into address coordinates in the frequency-amplitude table, the period-amplitude analysis saves considerable computational time. Thi~ feature and others allow the program to perform maxima-minima analysis on 5000 samples/sec in real time. Amplitude intervals selected for the table were 200 pV, providing a total range of 2.2 mV in some experiments while in others, the interval was 250 pV giving a range of 2.75 mV. The lower frequency bands were set at
jumps in which both hind limbs cleared the platform prior to landing.
Period-amplitude analysis To analyze selected bursts of EMG interference patterns from slow and fast extensors of the elbow or ankle, equal time intervals for fast and slow muscle, which encompassed the bursts without including prior or subsequent activity, were sampled at 5 0 0 0 samples per second and entered into a Hewlett-Packard 21 MX computer. Maxima and minima were detected in the signal by establishing critical points from which preceding and subsequent points differed by more than the noise threshold. For each m a x i m u m (Fig. 2A), the period between that m a x i m u m and the last maxim u m was computed along with the amplitude difference between that m a x i m u m and the last minimum. Minima were treated in a symmetric manner (Fig. 2B). The combination of
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Fig. 2. T w o illustrative events (A and B), taken from a single EMG burst such as those illustrated in Fig. 1, demonstrate the manner in w h i c h information is extracted from the signal. The c o m p u t e r printout o f periodamplitude analysis (C) s u m m a r i z e s the bursts o f EMG during four 90 cm jumps for the SOL. Samples per period and the resulting center frequencies are listed in the left c o l u m n s , original signal zero crossing periods in the middle (ZC), while the frequency-amplitude table is s h o w n at the right. Tabulated event A is circled in the table, while event B is s h o w n in a square.
57-1
B. BETTS, J.L. SMITH 6
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Fig. 3. T h e f r e q u e n c y - a m p l i t u d e table for SOL in Fig. 1 is displayed in graphic form o n t h e right, while a similar display for t h e same j u m p s for L G is s h o w n o n the left. A m p l i t u d e is displayed o n t h e X-axis ( h o r i z o n t a l l y ) , freq u e n c y o n the Z-axis ( o b l i q u e l y ) , a n d t h e n u m b e r o f events c o r r e s p o n d i n g t o a given f r e q u e n c y a n d a m p l i t u d e o n t h e Y-axis (vertically). Mean f r e q u e n c y a n d a m p l i t u d e for each m u s c l e are designated b y arrows.
20--30 c/sec while the highest frequency bands, due to the non-linear relationship between frequency and period, increased in size corresponding to consecutively smaller single periods as shown in Fig. 2C. Periods between zero crossings of the original signal were computed and tabulated in a separate column without associating amplitudes with them. A maximum of one such zero crossing of the original signal could be tabulated per maxima or minima, thus reducing noise in the analysis. Since the period between zero crossings of the original signal correspond to a half period of the wave rather than a full period as in maxima-minima analysis, each zero crossing was interpreted as indicating a wave having a period twice the observed time interval. Thus, the resolution for this variable was half as great at the highest frequencies as the maxima-minima analysis, leaving gaps in the zero crossing column as shown in Fig. 2C. In order to facilitate comparison of fastslow muscle pairs, frequency-amplitude tables, resulting from the period-amplitude
analysis of maxima and minima, were displayed graphically for each muscle of the pair. The table in Fig. 2C, which represents SOL bursts recorded during four 90 cm jumps, is shown on the right of Fig. 3, while the LG bursts for the same jumps are displayed on the left. As shown in Fig. 3, period-amplitude analysis is used to characterize the frequency (Z-axis) and amplitude (X-axis) distribution of events (Y-axis) in the EMG signal. Mean frequencies and amplitudes were determined by the computer in order to summarize data from slow and fast extensors for specific movements. These parameters were determined by summing the product of the center frequency of each band or center amplitude of each amplitude interval and the number of events in that band or interval and dividing that sum by the total number of events.
Results
For data collected during overground stepping and jumps that ranged in height from
PERIOD-AMPLITUDE ANALYSIS OF SLOW AND FAST EMG TABLE I Range of mean frequencies and amplitudes for period -amplitude analysis.
Frequency range (c/sec) Amplitude range (uV)
A. StepJump *
B. Treadmill **
LG
SOL
LT
ANC
307 650
59 257
126 239
45 67
* 3 cats: 56 jumps and 13 steps. ** 2 cats: 73 steps.
30 to 90 cm, such as the data in Figs. 1 and 3, the mean amplitude and frequency of SOL remained within a narrow range of values while the same parameters for LG increased markedly. Table I-A shows the group mean range of the average values of mean frequency and mean amplitude for individual steps and the highest jumps in three cats. A frequencyamplitude plot of period-amplitude analysis values for LG and SOL in Fig. 4 for one cat (T1) is representative of the three cats tested.
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Fig. 4. Frequency-amplitude plot of mean periodamplitude analysis values for EMG from LG and SOL for one cat (T1) during stepping and jumping. Each point represents mean + S.D. for the number of bursts given in parentheses below. For steps (5), open and closed circles represent LG and SOL. Open, slashed and closed triangles (LG) and squares (SOL) represent 30 (5), 60 (8), and 90 (5) cm jumps, respectively.
575
For all movements, SOL maintained an almost constant mean frequency between 382 and 396 c/sec with a mean standard deviation (S.D.) of 27 c/sec, while mean amplitude remained between 519 and 672 pV with a mean SD of 71 pV. In contrast, LG exhibited little or no activity during overground steps taken in approaching the jumps, which was expressed in the period-amplitude analysis as a mean frequency of 100--150 c/sec and mean amplitude just above the noise level (Fig. 4). For jumps, LG increased considerably from the parameters typical of stepping to a maximum of 615 c/sec (+65) and 1081 pV (+268) for 90 cm jumps. The apparent saturation at the highest jumps is due, at least in part, to the 1000 c/sec frequency c u t o f f of the telemetry (see Discussion). In all cats studied, both mean frequency and amplitude for LG achieved a m a x i m u m greater than that for SOL during the highest jumps with the exception of one cat (N1) in which the mean amplitude for LG remained low throughout the series of movements. During treadmill locomotion at speeds of 0.7--1.6 m/sec, LG was found to be either entirely inactive or minimally active at low mean frequencies and amplitudes of 2--300 c/sec and 3--400 pV, respectively. In some cats, LG exhibited a slight increase in mean frequency and amplitude throughout the range of treadmill speeds, while in others, no increase was seen. The slow extensor, SOL, was consistently active, staying within a narrow range of mean frequency and amplitude and exhibiting a very slight increase between a slow and a fast walk. The activity patterns for fast and slow forelimb extensors during treadmill locomotion were similar to those and hindlimb extensors during stepping and jumping, with ANC maintaining a relatively constant mean frequency and amplitude at all speeds studied, while LT showed a distinct increase in both parameters. Table I-B shows the group mean range of the average values for steps recorded at the lowest and highest treadmill speeds in two cats. A mean frequency-amplitude plot of period-am-
576
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PERIOD-AMPLITUDE ANALYSIS O F EMG FROM SLOW AND FAST EXTENSORS OF CAT D U R I N G LOCOMOTION AND JUMPING B. BETTS and J.L. SMITH
Neuromuscular Research Laboratory and Brain Research Institute, University o f California, Los Angeles, Calif. 90024 (U.S.A.)
(Accepted for publication: March 1, 1979)
Motor units can be separated into slow and fast contracting populations on the basis of their twitch contraction times (Wuerker et al. 1965; Mosher et al. 1972; Burke et al. 1973; Proske and Waite 1974). Most limb muscles are composed of a mixture of slow and fast units; however, in cats, extensor synergists such as the triceps surae (McPhedran et al. 1965; Ariano et al. 1973; Burke et al. 1974; Hammarberg 1974) and triceps brachii (Collatos et al. 1977} include one or more heads that are composed predominantly or totally of slow contracting units and one or more that are primarily composed of fast units. In studying the recruitment of fast and slow synergists at the ankle during unrestrained movements in cats, both Smith et al. (1977) and Walmsley et al. (1978) found that the peak of the rectified-averaged electromyogram (A-EMG) for the fast muscle closely reflected the kinetic demands of the movements, while the slow muscle showed a steady EMG level which was more independent of the m o v e m e n t kinetics. Although the peak of the A-EMG quantifies overall activity of the muscle, it provides no information a b o u t the frequency and amplitude distribution of the signal. Therefore, we sought a more detailed analysis for the raw EMG. In the past, raw EMG has been analyzed during normal movements (Grieve and Cavanagh 1973; Visser and de Rijke 1975; Komi and Viitasalo 1976) and in the diagnosis of myopathies using period analytic techniques (Willison 1964; Dowling et al. 1968;
Fusfeld 1971, 1972; Hirose and Sobue 1972}, while spectral analysis has been used in the detection of fatigue states (Sato 1965; Kadefors et al. 1968; Ortengren et al. 1975). Spectral analysis provides a description of the distribution of the total average power in a signal as a function of frequency (Ortengren 1975). Period analysis is based on the temporal distribution of 'critical points', specifically zero crossings of the signal or its first two derivatives, and the determination of the statistical distribution of those points; one of the most c o m m o n being mean zero crossing rate (Saltzberg 1973). Some of the analyses include amplitude measures (Willison 1964; Dowling et al. 1968; Hirose and Sobue 1972; Grieve and Cavanagh 1973; Komi and Viitasalo 1976}; however, none describes the two~iimensional period-amplitude distribution of the EMG, although interval-amplitude and period-amplitude analytic techniques have been recently applied to EEG (Leader et al. 1967; Legewie and Probst 1969; R~mond 1975; Harner and Ostergren 1976; Harner 1977). We have developed a real-time periodamplitude analysis program for EMG which is unique in that it stores events two-dimensionally, with coordinates given by the period and amplitude difference between maxima and minima. In addition, periods between zero crossings of the original signal are stored. In this way, most of the information in the raw EMG is retained in an easily interpreted form. We have found this technique of EMG analy-
B. BETTS, J.L. SMITH
572
sis useful in differentiating the activity patterns of slow and fast extensors at the elbow, which have not been previously studied, and at the ankle during unrestrained movements in cats. Preliminary results have been reported previously (Betts et al. 1977). ANO Methods
Data acquisition The lateral gastrocnemius (LG) and soleus (SOL) of the hind limb and the lateral head of the triceps brachii (LT) and anconeus (ANC) of the forelimb in five adult, female cats, weighing 2.3--3.3 kg, were chronically implanted under sodium pentobarbital using a technique described previously (Betts et al. 1976}. The implant, capable of 4 bipolar recordings, consisted of 8 electrode wires, made from multistranded stainless steel wire (Bergen microlin No. 9.6) with an outside diameter of 0.28 mm, 4 encased in each of two Silastic tubes and led from a head connector to the muscles to be implanted. In some of the forelimb implants, a smaller electrode wire (Bergen microlin No. 3.9) with an outside diameter of 0.2 mm was used. Each electrode, with 1 mm of insulation scraped, was threaded through a 22-gauge needle which had been passed through the muscle and was later removed leaving the exposed portion of the electrode embedded in the muscle. The pair of electrodes were placed within 1--2 mm of each other and sutured at their point of exit from the muscle. Both slow extensors, ANC and SOL, are composed totally of slow-twitch oxidative fibers, or type SO (Burke et al. 1974; Collatos et al. 1977}, while the fast extensors, LT and LG, are mixed muscles composed of 75--85% fasttwitch fibers with a higher percentage of fasttwitch glycolytic (FG} fibers than fast-twitch oxidative-glycolytic (FOG) fibers (Ariano et al. 1973; Collatos et al. 1977). During the recording sessions, a PAM-FM four-channel telemetry transmitter having a volume of 125 cu. cm (Biodata Systems, Los Angeles) was
]~mV 500 ms
Fig. 1. Typical telemetered electromyograms during an 80 cm jump to a platform recorded from lateral triceps (LT) anconeus (ANC), lateral gastrocnemius (LG) and soteus (SOL).
connected to the cat's skull plug for transmission of the myopotentials. The telemetry has a frequency response of 20--1000 c/sec and resulted in EMG recordings with a noise level of 150 pV p-p. Electromyograms, which were all full interference patterns as shown in Figure 1, were recorded on FM tape and a video system was used to synchronize the cat's movements with the associated EMG as described earlier (Betts et al. 1976). A BCD code, which changed every 2 sec, was used to synchronize all records. The cats were trained with food rewards to perform vertical jumps to a platform placed at 30--90 cm above the floor and run on a treadmill at speeds of 0.7--2.0 m/sec. Steps and jumps to be analyzed were selected by viewing the video record and choosing bursts of EMG which were artefact-free and related to normal steps during which the cat remained in a relatively fixed position on the treadmill, or
P E R I O D - A M P L I T U D E A N A L Y S I S OF SLOW AND F A S T EMG
period and amplitude constitutes an event, and events from one or more contractions of a single muscle were stored in a frequencyamplitude table (Fig. 2C). For example, the event in Fig. 2A is tabulated at a point corresponding to its computed amplitude of 2.2 mV and period of 5.0 msec (25 samples at 5000 samples per sec), which is expressed as a frequency of 200 c/sec (Fig. 2C). By converting computed periods and amplitudes immediately into address coordinates in the frequency-amplitude table, the period-amplitude analysis saves considerable computational time. Thi~ feature and others allow the program to perform maxima-minima analysis on 5000 samples/sec in real time. Amplitude intervals selected for the table were 200 pV, providing a total range of 2.2 mV in some experiments while in others, the interval was 250 pV giving a range of 2.75 mV. The lower frequency bands were set at
jumps in which both hind limbs cleared the platform prior to landing.
Period-amplitude analysis To analyze selected bursts of EMG interference patterns from slow and fast extensors of the elbow or ankle, equal time intervals for fast and slow muscle, which encompassed the bursts without including prior or subsequent activity, were sampled at 5 0 0 0 samples per second and entered into a Hewlett-Packard 21 MX computer. Maxima and minima were detected in the signal by establishing critical points from which preceding and subsequent points differed by more than the noise threshold. For each m a x i m u m (Fig. 2A), the period between that m a x i m u m and the last maxim u m was computed along with the amplitude difference between that m a x i m u m and the last minimum. Minima were treated in a symmetric manner (Fig. 2B). The combination of
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Fig. 2. T w o illustrative events (A and B), taken from a single EMG burst such as those illustrated in Fig. 1, demonstrate the manner in w h i c h information is extracted from the signal. The c o m p u t e r printout o f periodamplitude analysis (C) s u m m a r i z e s the bursts o f EMG during four 90 cm jumps for the SOL. Samples per period and the resulting center frequencies are listed in the left c o l u m n s , original signal zero crossing periods in the middle (ZC), while the frequency-amplitude table is s h o w n at the right. Tabulated event A is circled in the table, while event B is s h o w n in a square.
57-1
B. BETTS, J.L. SMITH 6
3
A
NO. O F EVENTS
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ANIPL I TUBE
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Fig. 3. T h e f r e q u e n c y - a m p l i t u d e table for SOL in Fig. 1 is displayed in graphic form o n t h e right, while a similar display for t h e same j u m p s for L G is s h o w n o n the left. A m p l i t u d e is displayed o n t h e X-axis ( h o r i z o n t a l l y ) , freq u e n c y o n the Z-axis ( o b l i q u e l y ) , a n d t h e n u m b e r o f events c o r r e s p o n d i n g t o a given f r e q u e n c y a n d a m p l i t u d e o n t h e Y-axis (vertically). Mean f r e q u e n c y a n d a m p l i t u d e for each m u s c l e are designated b y arrows.
20--30 c/sec while the highest frequency bands, due to the non-linear relationship between frequency and period, increased in size corresponding to consecutively smaller single periods as shown in Fig. 2C. Periods between zero crossings of the original signal were computed and tabulated in a separate column without associating amplitudes with them. A maximum of one such zero crossing of the original signal could be tabulated per maxima or minima, thus reducing noise in the analysis. Since the period between zero crossings of the original signal correspond to a half period of the wave rather than a full period as in maxima-minima analysis, each zero crossing was interpreted as indicating a wave having a period twice the observed time interval. Thus, the resolution for this variable was half as great at the highest frequencies as the maxima-minima analysis, leaving gaps in the zero crossing column as shown in Fig. 2C. In order to facilitate comparison of fastslow muscle pairs, frequency-amplitude tables, resulting from the period-amplitude
analysis of maxima and minima, were displayed graphically for each muscle of the pair. The table in Fig. 2C, which represents SOL bursts recorded during four 90 cm jumps, is shown on the right of Fig. 3, while the LG bursts for the same jumps are displayed on the left. As shown in Fig. 3, period-amplitude analysis is used to characterize the frequency (Z-axis) and amplitude (X-axis) distribution of events (Y-axis) in the EMG signal. Mean frequencies and amplitudes were determined by the computer in order to summarize data from slow and fast extensors for specific movements. These parameters were determined by summing the product of the center frequency of each band or center amplitude of each amplitude interval and the number of events in that band or interval and dividing that sum by the total number of events.
Results
For data collected during overground stepping and jumps that ranged in height from
PERIOD-AMPLITUDE ANALYSIS OF SLOW AND FAST EMG TABLE I Range of mean frequencies and amplitudes for period -amplitude analysis.
Frequency range (c/sec) Amplitude range (uV)
A. StepJump *
B. Treadmill **
LG
SOL
LT
ANC
307 650
59 257
126 239
45 67
* 3 cats: 56 jumps and 13 steps. ** 2 cats: 73 steps.
30 to 90 cm, such as the data in Figs. 1 and 3, the mean amplitude and frequency of SOL remained within a narrow range of values while the same parameters for LG increased markedly. Table I-A shows the group mean range of the average values of mean frequency and mean amplitude for individual steps and the highest jumps in three cats. A frequencyamplitude plot of period-amplitude analysis values for LG and SOL in Fig. 4 for one cat (T1) is representative of the three cats tested.
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F R E Q U E N C Y (HZ)
Fig. 4. Frequency-amplitude plot of mean periodamplitude analysis values for EMG from LG and SOL for one cat (T1) during stepping and jumping. Each point represents mean + S.D. for the number of bursts given in parentheses below. For steps (5), open and closed circles represent LG and SOL. Open, slashed and closed triangles (LG) and squares (SOL) represent 30 (5), 60 (8), and 90 (5) cm jumps, respectively.
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For all movements, SOL maintained an almost constant mean frequency between 382 and 396 c/sec with a mean standard deviation (S.D.) of 27 c/sec, while mean amplitude remained between 519 and 672 pV with a mean SD of 71 pV. In contrast, LG exhibited little or no activity during overground steps taken in approaching the jumps, which was expressed in the period-amplitude analysis as a mean frequency of 100--150 c/sec and mean amplitude just above the noise level (Fig. 4). For jumps, LG increased considerably from the parameters typical of stepping to a maximum of 615 c/sec (+65) and 1081 pV (+268) for 90 cm jumps. The apparent saturation at the highest jumps is due, at least in part, to the 1000 c/sec frequency c u t o f f of the telemetry (see Discussion). In all cats studied, both mean frequency and amplitude for LG achieved a m a x i m u m greater than that for SOL during the highest jumps with the exception of one cat (N1) in which the mean amplitude for LG remained low throughout the series of movements. During treadmill locomotion at speeds of 0.7--1.6 m/sec, LG was found to be either entirely inactive or minimally active at low mean frequencies and amplitudes of 2--300 c/sec and 3--400 pV, respectively. In some cats, LG exhibited a slight increase in mean frequency and amplitude throughout the range of treadmill speeds, while in others, no increase was seen. The slow extensor, SOL, was consistently active, staying within a narrow range of mean frequency and amplitude and exhibiting a very slight increase between a slow and a fast walk. The activity patterns for fast and slow forelimb extensors during treadmill locomotion were similar to those and hindlimb extensors during stepping and jumping, with ANC maintaining a relatively constant mean frequency and amplitude at all speeds studied, while LT showed a distinct increase in both parameters. Table I-B shows the group mean range of the average values for steps recorded at the lowest and highest treadmill speeds in two cats. A mean frequency-amplitude plot of period-am-
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