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11.10 The fractal dynamics of running
Chapter 11. Physiology of motor control: healthy and pathological human models' sitting position. A group of healthy, age-matched young adults were tested for comparison. Results: Compared with the controls (682.5±60.9N), quadriceps (549.0±69.3N) was significantly weaker in the ACL-D; activation failure was also evident (37.0%). The patella tendon SR of ACL-D appears to set off slower (onset latencies 23 & 26 ms in control and ACL-D knees respectively), with a much smaller amplitudes, and a slower rise and shorter duration. A reflexive hamstrings response was found at an earlier time in the ACL-D (29 ms, comparing to 32 ms of controls). Discussion: Quadriceps weakness in ACL-D and associated activation failure can be a result of reflexive inhibition as an autoregulation to compensate the loss of knee stability. This study also confirms the importance of hamstrings, via reflex regulation, in knee control after ACL injury. Conclusion: Knee rehabilitation after ACL injury should take into account the reflexive contribution of the ACL.
I1~
Modulation of the activity of a propriospinal reflex pathway during walking in man
$67
Results: Mean and SD of the stride interval decreased with increasing speed. Detrended fluctuation analysis showed that there were long range correlations present in the stride interval time series of running. The correlations followed a U-shaped function over increased running speed, reaching a minimum at the preferred running speed. The irregularity of the time series as indexed by ApEn peaked at the preferred running speed. Discussion: These results indicate that the preferred running speed, falling as it does between the upper and lower limits of possible running speeds, is the speed at which the most dynamic degrees of freedom are available for adaptive assembly of solutions to the coordination problem. Conclusion: Fluctuations in the stride interval time series of running exhibit long range correlations and are influenced by running speed.
References [1] Hausdorff JM, Peng CK, Ladin Z, Wei JY, Goldberger AL. Is walking a random walk? Evidence for long-range correlations in stride interval of human gait. J Appl Physiol 1995; 78:349 58.
C. Iglesias, J.B. Nielsen, V. Marchand-Pauvert. Physiologic
et Physiopathologie de la motricitd chez l'Homme, U731 INSERM/UPMC, Paris', France Introduction: In Humans, afferents from tibialis anterior (TA) facilitate the discharge of the quadriceps' (Q) motoneurones through lumbar propriospinal interneurones [1]. This reflex pathway plays a crucial role in the maintenance of the bipedal stance during walking [2]. In this study we tested the excitability of this reflex with respect to speeds of walking. Methods: Common peroneal nerve (CPN) stimulation induces two phases of excitation of the rectified Q electromyographic (EMG) activity, due respectively to group I and group II TA afferents (3). We compared the size of these responses in the Q EMG during treadmill walking at different speeds. Results: Although background Q EMG activity and CPN evoked responses rise with walking speed, at the subject's favorite speed (3 4 km,h l ), the two peaks of facilitation are greater than at slower or higher speeds. Discussion and Conclusion: At the preferred speed, considered as more automatic, it appears that the activity of the propriospinal pathway between TA and Q reaches its maximum. We assume that modifications of intrinsic properties make the spinal network more excitable at preferred walking speeds. These results suggest a role ofpropriospinal interneurones in the automatic control of gait in Humans. By analogy with the feline propriospinal system [3], these results also further support the existence of a locomotor CPG in Humans.
References [1] Simonetta-Moreau M e t al. Journal of Physiology, 1999; 517: 287 300. [2] Marchand-Pauvert V, Nieslen JB. Journal of Physiology, 2002; 538:647 57. [3] Rossignol S e t al. Brain Res Brain Res Rev. 2002; 40:257 66.
~The
fractal dynamics of running
K. Jordan 1, J.H. Challis 1, K.M. Newell 2. / The Pennsylvania State
University, USA," 2College of Health and Human Development, University Park, USA Introduction: Fluctuations in the stride interval time series of unconstrained walking are not random but exhibit long range correlations that decay as a power law [1]. To date these long range correlations have only been examined in walking. Here we examine whether the long range correlations are present in the stride interval time series during running. Methods: Recreational female runners were recruited for the study. They ran 8 rain trials at their preferred running speed as well as 10 and 20% slower and faster than their preferred speed.
I•
Effect of obstacle placement on the strategy used to cross over an obstacle during walking
M. Ladouceur, N. Gueguen, E.A. Gustafson, B. Floyd. Department
of Exercise Science, University of Iowa, USA Introduction: The purpose of the study was to determine if obstacle placement within the gait cycle was responsible for different motor strategies used in obstructed walking. Methods: Participants walked on a nine-meter walkway with an imbedded force-plate. Unilateral obstacles were positioned at midswing and late swing. Bilateral obstacles were positioned in late swing. Bony landmark positions (6) were defined using infrared markers and recorded using an Optotrack 3020 system. Results: The results showed a slope of the adaptation of the toe height equivalent to one. Furthermore, unilateral late swing obstacles and bilateral obstacles had approximately the same greater trochanter height adaptation whereas the unilateral mid-swing obstacles had a significantly different adaptation function. Discussion: Results from this experiment provide evidence that obstacle placement determines the proportion of motor strategies used.
I1~
Modulation of heteronymous recurrent inhibition between quadriceps and ankle muscles during walking in humans
J.C. Lamy, C. Iglesias, R. Katz, V. Marchand-Pauvert. U731 INSERM/UPMC; M~decine Physique et R~adaptation, La SalpOtri&re, Paris', France Introduction: In the human lower limb, heteronymous Ia excitation and matched recurrent inhibition (RI) are widely distributed, and many transjoint connections have been described, including projections from the quadriceps (Q) to both muscles soleus (SOL) and tibialis anterior (TA) of an antagonist pair operating at the ankle [1 ]. An appropriate control might be used to oppose activation of the muscle of the antagonist pair SOL-TA, which is unwanted during walking. Methods: Stimulation of the femoral nerve (FN) induced in both TA and SOL motoneurons a peak of heteronymous monosynaptic Ia excitation, followed by a trough, which is consistent with RI. The resulting effects of such a stimulation was assessed using rectified and averaged ongoing EMG activity in TA or SOL during (i) walking on a treadmill at preferred speed (ii) a voluntary Q-SOL or Q-TA co-contraction at matched levels of background EMG activity. Results: Heteronymous monosynaptic Ia excitation from Q remained unchanged whatever the motor task, whereas heteronymous RI from Q was deeply depressed during locomotor activities compared to tonic voluntary co-contraction.
I1~
Modulation of the activity of a propriospinal reflex pathway during walking in man
$67
Results: Mean and SD of the stride interval decreased with increasing speed. Detrended fluctuation analysis showed that there were long range correlations present in the stride interval time series of running. The correlations followed a U-shaped function over increased running speed, reaching a minimum at the preferred running speed. The irregularity of the time series as indexed by ApEn peaked at the preferred running speed. Discussion: These results indicate that the preferred running speed, falling as it does between the upper and lower limits of possible running speeds, is the speed at which the most dynamic degrees of freedom are available for adaptive assembly of solutions to the coordination problem. Conclusion: Fluctuations in the stride interval time series of running exhibit long range correlations and are influenced by running speed.
References [1] Hausdorff JM, Peng CK, Ladin Z, Wei JY, Goldberger AL. Is walking a random walk? Evidence for long-range correlations in stride interval of human gait. J Appl Physiol 1995; 78:349 58.
C. Iglesias, J.B. Nielsen, V. Marchand-Pauvert. Physiologic
et Physiopathologie de la motricitd chez l'Homme, U731 INSERM/UPMC, Paris', France Introduction: In Humans, afferents from tibialis anterior (TA) facilitate the discharge of the quadriceps' (Q) motoneurones through lumbar propriospinal interneurones [1]. This reflex pathway plays a crucial role in the maintenance of the bipedal stance during walking [2]. In this study we tested the excitability of this reflex with respect to speeds of walking. Methods: Common peroneal nerve (CPN) stimulation induces two phases of excitation of the rectified Q electromyographic (EMG) activity, due respectively to group I and group II TA afferents (3). We compared the size of these responses in the Q EMG during treadmill walking at different speeds. Results: Although background Q EMG activity and CPN evoked responses rise with walking speed, at the subject's favorite speed (3 4 km,h l ), the two peaks of facilitation are greater than at slower or higher speeds. Discussion and Conclusion: At the preferred speed, considered as more automatic, it appears that the activity of the propriospinal pathway between TA and Q reaches its maximum. We assume that modifications of intrinsic properties make the spinal network more excitable at preferred walking speeds. These results suggest a role ofpropriospinal interneurones in the automatic control of gait in Humans. By analogy with the feline propriospinal system [3], these results also further support the existence of a locomotor CPG in Humans.
References [1] Simonetta-Moreau M e t al. Journal of Physiology, 1999; 517: 287 300. [2] Marchand-Pauvert V, Nieslen JB. Journal of Physiology, 2002; 538:647 57. [3] Rossignol S e t al. Brain Res Brain Res Rev. 2002; 40:257 66.
~The
fractal dynamics of running
K. Jordan 1, J.H. Challis 1, K.M. Newell 2. / The Pennsylvania State
University, USA," 2College of Health and Human Development, University Park, USA Introduction: Fluctuations in the stride interval time series of unconstrained walking are not random but exhibit long range correlations that decay as a power law [1]. To date these long range correlations have only been examined in walking. Here we examine whether the long range correlations are present in the stride interval time series during running. Methods: Recreational female runners were recruited for the study. They ran 8 rain trials at their preferred running speed as well as 10 and 20% slower and faster than their preferred speed.
I•
Effect of obstacle placement on the strategy used to cross over an obstacle during walking
M. Ladouceur, N. Gueguen, E.A. Gustafson, B. Floyd. Department
of Exercise Science, University of Iowa, USA Introduction: The purpose of the study was to determine if obstacle placement within the gait cycle was responsible for different motor strategies used in obstructed walking. Methods: Participants walked on a nine-meter walkway with an imbedded force-plate. Unilateral obstacles were positioned at midswing and late swing. Bilateral obstacles were positioned in late swing. Bony landmark positions (6) were defined using infrared markers and recorded using an Optotrack 3020 system. Results: The results showed a slope of the adaptation of the toe height equivalent to one. Furthermore, unilateral late swing obstacles and bilateral obstacles had approximately the same greater trochanter height adaptation whereas the unilateral mid-swing obstacles had a significantly different adaptation function. Discussion: Results from this experiment provide evidence that obstacle placement determines the proportion of motor strategies used.
I1~
Modulation of heteronymous recurrent inhibition between quadriceps and ankle muscles during walking in humans
J.C. Lamy, C. Iglesias, R. Katz, V. Marchand-Pauvert. U731 INSERM/UPMC; M~decine Physique et R~adaptation, La SalpOtri&re, Paris', France Introduction: In the human lower limb, heteronymous Ia excitation and matched recurrent inhibition (RI) are widely distributed, and many transjoint connections have been described, including projections from the quadriceps (Q) to both muscles soleus (SOL) and tibialis anterior (TA) of an antagonist pair operating at the ankle [1 ]. An appropriate control might be used to oppose activation of the muscle of the antagonist pair SOL-TA, which is unwanted during walking. Methods: Stimulation of the femoral nerve (FN) induced in both TA and SOL motoneurons a peak of heteronymous monosynaptic Ia excitation, followed by a trough, which is consistent with RI. The resulting effects of such a stimulation was assessed using rectified and averaged ongoing EMG activity in TA or SOL during (i) walking on a treadmill at preferred speed (ii) a voluntary Q-SOL or Q-TA co-contraction at matched levels of background EMG activity. Results: Heteronymous monosynaptic Ia excitation from Q remained unchanged whatever the motor task, whereas heteronymous RI from Q was deeply depressed during locomotor activities compared to tonic voluntary co-contraction.