.-lzta
Physiol Scatid 1990, 138, 575-576
Differences in modulation of the gastrocnemius and soleus H-reflexes during hopping in man T. M O R I T A N I , L. O D D S S O N and A. T H O R S T E N S S O N Department of Physiology 111, Karolinska Institute, Stockholm, Sweden
The Hoffmann reflex, or H-reflex, has been established as a means of investigating the gain of the stretch reflex during various motor tasks in man (Stein & Capaday 1988). During walking this largely monosynaptic reflex was modulated for the ‘slow’ soleus muscle during different phases of the stride cycle and a higher excitability paralleled an increased E M G during stance (Capaday & Stein 1987). Interestingly, the H-reflex was lower in running than in walking despite a higher soleus E M G activity and a faster speed, indicating an influence of central neural mechanisms, acting through, for example, presynaptic inhibition (Capaday & Stein 1987). Recordings from the other main ankle extensor synergist, the relatively ‘fast’ gastrocnemius muscle, were not obtained. Using another stereotyped cyclic motor task, repetitive hopping in place, we have recently reported a phase-dependent and preferential activation of the gastrocnemius muscle with increasing demands of force and speed (Oddsson et al. 1988, Thorstensson et al. 1988, see also Moritani et a/. 1989),which is in line with observations on animals (e.g. Smith et al. 1977). This appears to be a functional adjustment since a fast muscle would be more apt to fulfil the demands of rapid alternating forceful motor activities. The aim was to elucidate further the mechanisms behind these differences in recruitment pattern by comparing H-reflex amplitude and E M G recorded simultaneously from the soleus and gastrocnemius muscles in different phases of the movement cycle during hopping of graded intensity. A single electrical stimulation was applied to the tibial nerve and adjusted to elicit two discrete action potentials in the calf muscles. The first evoked potential, the M-wave, originates from the direct stimulation of motor axons, and the second one, the H-wave, results from stimulation of the largest sensory axons (group Ia afferents from muscle spindles) which have a strong monosynaptic projection onto aReceived 8 January 1990, accepted 19 January 1990. Key words: muscle fibre types, preferential recruitment, spinal reflex excitability. Correspondence : Alf Thorstensson, Department of Physiology 111, Karolinska Institute, Lidingovagen I , S-I 14 33 Stockholm, Sweden.
motoneurons. The amplitude of the H-wave during hopping was compared to that during quiet standing to get a measure of spinal reflex modulation. Miniature-sized surface electrodes were used to stimulate the tibial nerve in the popliteal fossa and to record the E M G from the medial gastrocnemius and . cf. Hugon 1973). soleus muscles (Moritani et ~ l1985, One male subject (34 years, 1.81 m, 7 j kg) performed three different types of hopping (knees straight) on a force platform with the mean hopping height, frequency, contact time and mechanical power at 1.7, 6.2 and 26.7 cm; 3.6, 2.6 and 1 . 6Hz; 162, 161 and 157 ms; and 285,654 and ZOI I W, for small, light and max hopping respectively. (Coefficient of variation was less than 6% for all mechanical variables, except height, IO%, and power, 8%, for the small hopping.) Each hopping cycle was divided into 36 different ro-ms intervals (see Fig. I ) . A single rectangular pulse s was delivered in one of these of 5 0 0 , ~ ~duration intervals during each cycle in a set of consecutive hops. The order of stimulated intervals was randomized. A foot switch and a variable time delay circuit were used to trigger the stimulator. Spiketriggered averaging was employed to isolate the Hreflex potentials from the background EMG. A minimum of 10 signals was needed in the averaging, i.e. at least 360 hops had to be performed for each of the three types of hopping. The amplitude of the Hreflex was normalized to that during relaxed standing obtained at the beginning of each testing session (see Fig. I). Results indicated that the H-reflex amplitude (H(,:,,) was modulated in both soleus (SOL) and medial gastrocnemius (MG) during the hopping cycle (Fig. I). The relative amplitude of the H-wave started to increase before foot contact and reached its peak at or shortly after (Fig. I). During the main part of the airborne phase, where the E M G was low or absent, there was no or moderate increases in H,,,,. The peak H-reflex amplitude increased markedly more over the resting control values for the M G as compared to the SOL, approximately 3.8, 4.2 and 5.0 times versus 4.2, 3.1 and 1.6 times during small, light and max hopping respectively. H-reflex amplitude changes preceded the force curves by 45, 58 and 67 ms for MG and 39, 59 and j 4 m s for SOL as revealed by computerimplemented cross-correlation analyses.
575
j76
T. .?.foritiini et rrl. d r
.
SOL
ments. This modulation occurs in relation to different phases of a cyclic movement as well as to a varying degree in fast and slow synergistic muscles, here gastrocnemius and soleus, depending on the demands of force and speed of the motor activity. This stud!- was supported by grants from the Research Council of the Swedish Sports Federation and the Karolinska Institute, Sweden, and the Institute for Medicine and Sport Sciences, Nagoya, Japan. T. hloritani was the first recipient of the scholarship for international eschange of researchers from Sveriges Centralforening for Idrottens Framjande. The present address for T. Moritani: Laborator! of Applied Physiology, College of Liberal Arts and Sciences. Kyoto University, Kyoto 606, Japan.
REFERENCES C. & STEIN, R.B. 1987. Difference in the amplitude of the human soleus €-I reflex during walking and running. f Ph,ysiol 392, 513-522. H L G o ~ ,31. 1973. Methodology of thc Hoffmann Zi‘Z - : 6 ? - 1 2 8 -8J - 4 E I: 40 E2 I20 :in 2 B 8 reflex in man. I n : J. E. Desmedt (ed.) Nim Dmeloptime(ms1 merits in Elertrotnyography nnd Clinicul Nrrtrop l i . ) ~ s r o l o ~pp. ~ ~ ,277-293. Karger, Rasle. Fig. I . .It!-pical set of computer outputs for maximal T., MURO, M. & K I J I M A , A. 1985. hopping trials (height 27 cm, power 2 0 1 0 \V, contact MORITANI, Electromechanical changes during electrically intinie I j7 ms). Upper four traces shov the time course duced and maximal voluntary contractions : electrochanges of vertical force and the rectified and filtcired physiologic responses of different muscle fiber (5 1000 IIz) E l I G s from the tibialis anterior (I..\). types during stimulated contractions. E s p Neurol soleus (SOL) and medial gastrocnemius (1iG) 88, 471-483. muscles. The lower two graphs show the corrcsponding SOI, and MCi H-reflex changes (H-,,,) &IORITANI, T . , ODDSSON, L. & ‘FHORSTENSSON, A. 1989. Neural and biomechanical differences benormalized to the standing rest control d u e s (H,,,,]!). tween men and young boys during a variety of Zero time indicates onset of ground contact (see f i x e motor tasks. .qctcz Physiol Scund 1 3 7 ~347-355. curxe on top). Each data point represents an average of 20 trials. .\ line was fitted to each set of data points ODDSSOS, L., MORITANI, -r. & THORNSTENSSON, A. 1988. Phase dependent changes in activation levels b! ,I ninth-degree pol! nomial function. between the soleus and gastrocnemius muscles in man during different forms of hopping. ComThus. the spinal reflex gain (largel! the m c m munication to the 7th Congress of the International s! naptic component) appeared 10 be modulated IU a Society of Electrophysiological Kinesiology, diferent degree in the t \ \ n functionall! spccial Enschede, Holland. muscles, i.e. a decrease for the ‘slou * soleus and an SMITH, J.L., BETTS, B., EDGERTON, V.R. & COLLATOS, increase for the relati1 el! ’ tist’ medial gastrocnemius T.C. 1977. EhlG of slow and fast ankle extensors of with increasing demands of forcc And speed. The cat during posture, locomotion and jumping. f corresponding niyoelectric actix it! increased in both .\-eitroph,ysinl 49. 503--5 I 3. muscles. but significantl!- more in the gastrocnemius S T E I N , R.B. & CAPADAY, C. 1988. The modulation of human reflexes during functional motor tasks. (Thorstensson P / ~ r l .1988). In locomotion. Capaday S7’rmds .\CPurol Sri I I , 328-332. Stein (1987) have demonstrated that the H-reflex of 7’. & ODDSSON, I,. the soleus is actually decreased in running as cornpiired TIIORSTENSSON,A,, MORITANI, 1988. Task specificit)- in activation patterns of the with walking. Preliminary results of our own indicate soleus and gastrocnemius muscles in man. Coman opposite pattern for the gastrocnemius. munication to the 7th Congress of the International .\vailable experimental results suggest that spinal Society of Electrophysiological Kinesiology, refleies are not stereotj-ped motor patterns, but can be Enschede, Holland. specifically modulated for different functional requireCAPADAY,
Physiol Scatid 1990, 138, 575-576
Differences in modulation of the gastrocnemius and soleus H-reflexes during hopping in man T. M O R I T A N I , L. O D D S S O N and A. T H O R S T E N S S O N Department of Physiology 111, Karolinska Institute, Stockholm, Sweden
The Hoffmann reflex, or H-reflex, has been established as a means of investigating the gain of the stretch reflex during various motor tasks in man (Stein & Capaday 1988). During walking this largely monosynaptic reflex was modulated for the ‘slow’ soleus muscle during different phases of the stride cycle and a higher excitability paralleled an increased E M G during stance (Capaday & Stein 1987). Interestingly, the H-reflex was lower in running than in walking despite a higher soleus E M G activity and a faster speed, indicating an influence of central neural mechanisms, acting through, for example, presynaptic inhibition (Capaday & Stein 1987). Recordings from the other main ankle extensor synergist, the relatively ‘fast’ gastrocnemius muscle, were not obtained. Using another stereotyped cyclic motor task, repetitive hopping in place, we have recently reported a phase-dependent and preferential activation of the gastrocnemius muscle with increasing demands of force and speed (Oddsson et al. 1988, Thorstensson et al. 1988, see also Moritani et a/. 1989),which is in line with observations on animals (e.g. Smith et al. 1977). This appears to be a functional adjustment since a fast muscle would be more apt to fulfil the demands of rapid alternating forceful motor activities. The aim was to elucidate further the mechanisms behind these differences in recruitment pattern by comparing H-reflex amplitude and E M G recorded simultaneously from the soleus and gastrocnemius muscles in different phases of the movement cycle during hopping of graded intensity. A single electrical stimulation was applied to the tibial nerve and adjusted to elicit two discrete action potentials in the calf muscles. The first evoked potential, the M-wave, originates from the direct stimulation of motor axons, and the second one, the H-wave, results from stimulation of the largest sensory axons (group Ia afferents from muscle spindles) which have a strong monosynaptic projection onto aReceived 8 January 1990, accepted 19 January 1990. Key words: muscle fibre types, preferential recruitment, spinal reflex excitability. Correspondence : Alf Thorstensson, Department of Physiology 111, Karolinska Institute, Lidingovagen I , S-I 14 33 Stockholm, Sweden.
motoneurons. The amplitude of the H-wave during hopping was compared to that during quiet standing to get a measure of spinal reflex modulation. Miniature-sized surface electrodes were used to stimulate the tibial nerve in the popliteal fossa and to record the E M G from the medial gastrocnemius and . cf. Hugon 1973). soleus muscles (Moritani et ~ l1985, One male subject (34 years, 1.81 m, 7 j kg) performed three different types of hopping (knees straight) on a force platform with the mean hopping height, frequency, contact time and mechanical power at 1.7, 6.2 and 26.7 cm; 3.6, 2.6 and 1 . 6Hz; 162, 161 and 157 ms; and 285,654 and ZOI I W, for small, light and max hopping respectively. (Coefficient of variation was less than 6% for all mechanical variables, except height, IO%, and power, 8%, for the small hopping.) Each hopping cycle was divided into 36 different ro-ms intervals (see Fig. I ) . A single rectangular pulse s was delivered in one of these of 5 0 0 , ~ ~duration intervals during each cycle in a set of consecutive hops. The order of stimulated intervals was randomized. A foot switch and a variable time delay circuit were used to trigger the stimulator. Spiketriggered averaging was employed to isolate the Hreflex potentials from the background EMG. A minimum of 10 signals was needed in the averaging, i.e. at least 360 hops had to be performed for each of the three types of hopping. The amplitude of the Hreflex was normalized to that during relaxed standing obtained at the beginning of each testing session (see Fig. I). Results indicated that the H-reflex amplitude (H(,:,,) was modulated in both soleus (SOL) and medial gastrocnemius (MG) during the hopping cycle (Fig. I). The relative amplitude of the H-wave started to increase before foot contact and reached its peak at or shortly after (Fig. I). During the main part of the airborne phase, where the E M G was low or absent, there was no or moderate increases in H,,,,. The peak H-reflex amplitude increased markedly more over the resting control values for the M G as compared to the SOL, approximately 3.8, 4.2 and 5.0 times versus 4.2, 3.1 and 1.6 times during small, light and max hopping respectively. H-reflex amplitude changes preceded the force curves by 45, 58 and 67 ms for MG and 39, 59 and j 4 m s for SOL as revealed by computerimplemented cross-correlation analyses.
575
j76
T. .?.foritiini et rrl. d r
.
SOL
ments. This modulation occurs in relation to different phases of a cyclic movement as well as to a varying degree in fast and slow synergistic muscles, here gastrocnemius and soleus, depending on the demands of force and speed of the motor activity. This stud!- was supported by grants from the Research Council of the Swedish Sports Federation and the Karolinska Institute, Sweden, and the Institute for Medicine and Sport Sciences, Nagoya, Japan. T. hloritani was the first recipient of the scholarship for international eschange of researchers from Sveriges Centralforening for Idrottens Framjande. The present address for T. Moritani: Laborator! of Applied Physiology, College of Liberal Arts and Sciences. Kyoto University, Kyoto 606, Japan.
REFERENCES C. & STEIN, R.B. 1987. Difference in the amplitude of the human soleus €-I reflex during walking and running. f Ph,ysiol 392, 513-522. H L G o ~ ,31. 1973. Methodology of thc Hoffmann Zi‘Z - : 6 ? - 1 2 8 -8J - 4 E I: 40 E2 I20 :in 2 B 8 reflex in man. I n : J. E. Desmedt (ed.) Nim Dmeloptime(ms1 merits in Elertrotnyography nnd Clinicul Nrrtrop l i . ) ~ s r o l o ~pp. ~ ~ ,277-293. Karger, Rasle. Fig. I . .It!-pical set of computer outputs for maximal T., MURO, M. & K I J I M A , A. 1985. hopping trials (height 27 cm, power 2 0 1 0 \V, contact MORITANI, Electromechanical changes during electrically intinie I j7 ms). Upper four traces shov the time course duced and maximal voluntary contractions : electrochanges of vertical force and the rectified and filtcired physiologic responses of different muscle fiber (5 1000 IIz) E l I G s from the tibialis anterior (I..\). types during stimulated contractions. E s p Neurol soleus (SOL) and medial gastrocnemius (1iG) 88, 471-483. muscles. The lower two graphs show the corrcsponding SOI, and MCi H-reflex changes (H-,,,) &IORITANI, T . , ODDSSON, L. & ‘FHORSTENSSON, A. 1989. Neural and biomechanical differences benormalized to the standing rest control d u e s (H,,,,]!). tween men and young boys during a variety of Zero time indicates onset of ground contact (see f i x e motor tasks. .qctcz Physiol Scund 1 3 7 ~347-355. curxe on top). Each data point represents an average of 20 trials. .\ line was fitted to each set of data points ODDSSOS, L., MORITANI, -r. & THORNSTENSSON, A. 1988. Phase dependent changes in activation levels b! ,I ninth-degree pol! nomial function. between the soleus and gastrocnemius muscles in man during different forms of hopping. ComThus. the spinal reflex gain (largel! the m c m munication to the 7th Congress of the International s! naptic component) appeared 10 be modulated IU a Society of Electrophysiological Kinesiology, diferent degree in the t \ \ n functionall! spccial Enschede, Holland. muscles, i.e. a decrease for the ‘slou * soleus and an SMITH, J.L., BETTS, B., EDGERTON, V.R. & COLLATOS, increase for the relati1 el! ’ tist’ medial gastrocnemius T.C. 1977. EhlG of slow and fast ankle extensors of with increasing demands of forcc And speed. The cat during posture, locomotion and jumping. f corresponding niyoelectric actix it! increased in both .\-eitroph,ysinl 49. 503--5 I 3. muscles. but significantl!- more in the gastrocnemius S T E I N , R.B. & CAPADAY, C. 1988. The modulation of human reflexes during functional motor tasks. (Thorstensson P / ~ r l .1988). In locomotion. Capaday S7’rmds .\CPurol Sri I I , 328-332. Stein (1987) have demonstrated that the H-reflex of 7’. & ODDSSON, I,. the soleus is actually decreased in running as cornpiired TIIORSTENSSON,A,, MORITANI, 1988. Task specificit)- in activation patterns of the with walking. Preliminary results of our own indicate soleus and gastrocnemius muscles in man. Coman opposite pattern for the gastrocnemius. munication to the 7th Congress of the International .\vailable experimental results suggest that spinal Society of Electrophysiological Kinesiology, refleies are not stereotj-ped motor patterns, but can be Enschede, Holland. specifically modulated for different functional requireCAPADAY,
