Statistical Considerations When Assessing Short Latency Stretch Reflexes in the Human Soleus Muscle

The aim was to investigate trial-by-trial response characteristics in the short-latency stretch reflex (SSR). Fourteen dorsiflexion stretches were applied to the ankle joint with a precontracted soleus muscle on 2 days. The magnitude and variability of trial-by-trial responses of the SSR were assessed. The SSR was log-normally distributed and variance heterogeneous between subjects. For some subjects, the magnitude and variance differed between days and stretches. As velocity increased, variance heterogeneity tended to decrease and response magnitude increased. The current study demonstrates the need to assess trial-by-trial response characteristics and not averaged curves. Moreover, it provides an analysis of SSR characteristics accounting for log-normally distributed and variance heterogeneous trial-by-trial responses.

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Effects of contraction intensity on muscle fascicle and stretch reflex behavior in the human triceps surae

Journal of Applied Physiology ◽

10.1152/japplphysiol.90432.2008 ◽

2008 ◽

Vol 105 (1) ◽

pp. 226-232 ◽

Cited By ~ 27

Author(s):

Neil J. Cronin ◽

Jussi Peltonen ◽

Masaki Ishikawa ◽

Paavo V. Komi ◽

Janne Avela ◽

...

Keyword(s):

Stretch Reflex ◽

Force Production ◽

Voluntary Contraction ◽

Short Latency ◽

Afferent Feedback ◽

Triceps Surae ◽

Medial Gastrocnemius ◽

Stretch Reflexes ◽

Muscle Fascicle ◽

Human Triceps Surae

The aims of this study were to examine changes in the distribution of a stretch to the muscle fascicles with changes in contraction intensity in the human triceps surae and to relate fascicle stretch responses to short-latency stretch reflex behavior. Thirteen healthy subjects were seated in an ankle ergometer, and dorsiflexion stretches (8°; 250°/s) were applied to the triceps surae at different moment levels (0–100% of maximal voluntary contraction). Surface EMG was recorded in the medial gastrocnemius, soleus, and tibialis anterior muscles, and ultrasound was used to measure medial gastrocnemius and soleus fascicle lengths. At low forces, reflex amplitudes increased despite a lack of change or even a decrease in fascicle stretch velocities. At high forces, lower fascicle stretch velocities coincided with smaller stretch reflexes. The results revealed a decline in fascicle stretch velocity of over 50% between passive conditions and maximal force levels in the major muscles of the triceps surae. This is likely to be an important factor related to the decline in stretch reflex amplitudes at high forces. Because short-latency stretch reflexes contribute to force production and stiffness regulation of human muscle fibers, a reduction in afferent feedback from muscle spindles could decrease the efficacy of human movements involving the triceps surae, particularly where high force production is required.

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Sympathetic outflow enhances the stretch reflex response in the relaxed soleus muscle in humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.00955.2004 ◽

2005 ◽

Vol 98 (4) ◽

pp. 1366-1370 ◽

Cited By ~ 16

Author(s):

Nis Hjortskov ◽

Jørgen Skotte ◽

Christian Hye-Knudsen ◽

Nils Fallentin

Keyword(s):

Soleus Muscle ◽

Stretch Reflex ◽

Mental Arithmetic ◽

Muscle Spindles ◽

Short Latency ◽

Reflex Response ◽

Sympathetic Outflow ◽

Direct Influence ◽

Handgrip Exercise ◽

Sympathetic Nervous

Animal experiments suggest that an increase in sympathetic outflow can depress muscle spindle sensitivity and thus modulate the stretch reflex response. The results are, however, controversial, and human studies have failed to demonstrate a direct influence of the sympathetic nervous system on the sensitivity of muscle spindles. We studied the effect of increased sympathetic outflow on the short-latency stretch reflex in the soleus muscle evoked by tapping the Achilles tendon. Nine subjects performed three maneuvers causing a sustained activation of sympathetic outflow to the leg: 3 min of static handgrip exercise at 30% of maximal voluntary contraction, followed by 3 min of posthandgrip ischemia, and finally during a 3-min mental arithmetic task. Electromyography was measured from the soleus muscle with bipolar surface electrodes during the Achilles tendon tapping, and beat-to-beat changes in heart rate and mean arterial blood pressure were monitored continuously. Mean arterial pressure was significantly elevated during all three maneuvers, whereas heart rate was significantly elevated during static handgrip exercise and mental arithmetic but not during posthandgrip ischemia. The peak-to-peak amplitude of the short-latency stretch reflex was significantly increased during mental arithmetic ( P < 0.05), static handgrip exercise ( P < 0.001), and posthandgrip ischemia ( P < 0.005). When expressed in percent change from rest, the mean peak-to-peak amplitude increased by 111 (SD 100)% during mental arithmetic, by 160 (SD 103)% during static handgrip exercise, and by 90 (SD 67)% during posthandgrip ischemia. The study clearly indicates a facilitation of the short-latency stretch reflex during increased sympathetic outflow. We note that the enhanced stretch reflex responses observed in relaxed muscles in the absence of skeletomotor activity support the idea that the sympathetic nervous system can exert a direct influence on the human muscle spindles.

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Soleus stretch reflex modulation during gait in humans

Journal of Neurophysiology ◽

10.1152/jn.1996.76.2.1112 ◽

1996 ◽

Vol 76 (2) ◽

pp. 1112-1120 ◽

Cited By ~ 171

Author(s):

T. Sinkjaer ◽

J. B. Andersen ◽

B. Larsen

Keyword(s):

Ankle Joint ◽

Stretch Reflex ◽

Stance Phase ◽

Short Latency ◽

Reflex Modulation ◽

Total System ◽

Step Cycle ◽

Healthy Human ◽

Phase Lead ◽

Heel Contact

1. The modulation of the short-latency stretch reflex during walking at different walking speeds was investigated and compared with the stretch reflex during standing in healthy human subjects. 2. Ankle joint stretches were applied by a system able to rotate the human ankle joint during treadmill walking in any phase of the step cycle. The system consisted of a mechanical joint attached to the subject's ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. The weight of the total system attached to the leg of the subject was 900 g. 3. The short-latency soleus stretch reflex was modulated during a step. In the stance phase, the amplitude equaled that found during standing at matched soleus background electromyogram (EMG). In the transition from stance to swing, the amplitude was 0 in all subjects. In late swing, the stretch reflex amplitude increased to 45 +/- 27% (mean +/- SD) of the maximal amplitude in the stance phase (stretch amplitude 8 degrees, stretch velocity 250 degrees/s). 4. The onset (42 +/- 3.2 ms) and peak latencies (59 +/- 2.5 ms) of the stretch reflex did not depend on the phase in the step cycle at which the reflex was elicited. 5. When the ankle joint is rotated, a change in torque can be measured. The torque measured over the first 35 ms after stretch onset (nonreflex torque) was at a maximum during late stance, when the leg supported a large part of the body's weight, and at a minimum during the swing phase. At heel contact the nonreflex torque was 50% of its maximal value. 6. During the stance phase the maximal EMG stretch reflex had a phase lead of approximately 120 ms with respect to the maximal background EMG and a phase lead of approximately 250 ms with respect to the maximal nonreflex torque. 7. The constant latency of the stretch reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. 8. The relatively high amplitude of the stretch reflex in late swing and at heel contact made it likely that the stretch reflex contributed to the activation of the ankle extensor muscles in early stance phase.

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Changes in the excitability of soleus muscle short latency stretch reflexes during human hopping after 4 weeks of hopping training

European Journal of Applied Physiology ◽

10.1007/s004210050455 ◽

1998 ◽

Vol 78 (6) ◽

pp. 522-532 ◽

Cited By ~ 72

Author(s):

Michael Voigt ◽

Fabio Chelli ◽

Carlo Frigo

Keyword(s):

Soleus Muscle ◽

Short Latency ◽

Stretch Reflexes

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Short-latency stretch reflex modulation in response to varying soleus muscle activities

Journal of Electromyography and Kinesiology ◽

10.1016/s1050-6411(01)00030-x ◽

2002 ◽

Vol 12 (1) ◽

pp. 17-26 ◽

Cited By ~ 11

Author(s):

K Ogiso ◽

J.M McBride ◽

T Finni ◽

P.V Komi

Keyword(s):

Soleus Muscle ◽

Stretch Reflex ◽

Short Latency ◽

Reflex Modulation

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Guided intrathecal baclofen administration by using soleus stretch reflex in moderate-severe spastic multiple sclerosis patients with implanted pump

Multiple Sclerosis Journal ◽

10.1191/1352458504ms1092oa ◽

2004 ◽

Vol 10 (5) ◽

pp. 521-525 ◽

Cited By ~ 5

Author(s):

J F Nielsen ◽

T Sinkjær

Keyword(s):

Multiple Sclerosis ◽

Ankle Joint ◽

Clinical Assessment ◽

Strong Correlation ◽

Stretch Reflex ◽

Intrathecal Baclofen ◽

Short Latency ◽

Severe Spasticity ◽

Multiple Sclerosis Patients ◽

Ashworth Scale

We tested the hypothesis that changes in soleus stretch reflex was correlated to changes in intrathecal baclofen dose in 12 multiple sclerosis patients with moderate-severe spasticity treated with intrathecal baclofen pump. Twice patients were evaluated clinically and biomechanically. The short-latency soleus stretch reflex was elicited by rotating the ankle joint 48 with a velocity from 3.1 to 1808/s. There was a strong correlation between changes in intrathecal baclofen dose and amplitude of the short-latency stretch reflex (r=- 0.88, PB < 0.001), which means that with an increase in baclofen dose there is a decrease in the amplitude. In contrast, no correlation exists between changes in intrathecal baclofen dose and clinical assessment of spasticity by using the Ashworth scale. The amplitude of the stretch reflex was very small (5 mV) compared with previous findings (> 50 μV), which indicates an effective antispastic effect of intrathecal baclofen. We suggest that clinical evaluation of spasticity using Ashworth scale is insensitive to detect minor changes in moderate-severe spasticity and consequently might not be very useful in evaluating spasticity in relation to ambulatory filling of baclofen pumps. The soleus stretch reflex might be useful in situations when there is doubt about the effect of intrathecally administered baclofen.

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