Knee joint angular velocities and accelerations during the patellar tendon jerk
Highlights
► In this study, we used a noninvasive, ultrasound technique to measure the muscle kinematics during a standard neurological, tendon reflex test. ► We found that muscle accelerations but not velocities exceed the ranges encountered in ADLs. ► We provided experimental evidence to support the common belief that muscle kinematic ranges during TJ exceed the kinematic range of ADLs for accelerations but not velocities.
Introduction
The human body remains in a state of homeostasis with the environment. This means that the execution of various human motor functions is possible within certain ranges of environmental change. The larger the range of environmental changes the more adaptive is the system. An effective interaction with the environment requires optimal sensitivity to both internal physiological signals and external stimuli. Excessive sensitivity to external stimuli and inadequate sensitivity to internal physiological signals can impede voluntary action.
Increased muscle activation (neural sensitivity) to displacement, which manifests clinically as hyperreflexia, is characteristic of many neurological diseases such as stroke, traumatic brain or spinal cord injury, and cerebral palsy. Such over activity of muscle may contribute to hypertonia, defined as an increased resistance to passive stretch. Hypertonia usually limits the execution of voluntary movements, but it also means that mechanical sensitivity of the limb (muscle displacement as a result of applied external force), is decreased.
The muscle stretch reflex (SR) is involuntary muscle activation in response to stretch, which plays a major role in hyperreflexia. Under physiological conditions, muscle stretch may be caused by either passive or active lengthening of a muscle operating across a joint. Passive stretch of a muscle may be caused by external forces applied to the body segment, whereas active stretch may be caused by activation of antagonistic muscle groups. SR consists of a synchronized series of bursts of muscle activation in response to stretch. The amplitude and timing of SR are determined by the stretch characteristics (amplitude, velocity, and duration), the pre-existing state of the muscle (level of activation, length, and velocity), the type of motor activity being executed by an individual and a substantial stochastic component (Lee and Tatton, 1975, Stein and Thompson, 2006).
The fastest component of SR (also known as: M1, phasic, monosynaptic or short latency reflex) originates from activation of Ia muscle spindle afferents and activation of the motoneuron pool of muscle through monosynaptic connections in the spinal cord (Magladery, 1955, Laporte and Lloyd, 1952). The contributions of various pathways to the slower components of SR are less clear and include: responses from II muscle spindle afferents to the polysynaptic spinal and supraspinal pathways and late oscillatory responses from Ia afferents (Eklund et al., 1982, Matthews, 2006). The functional role of SR in biomechanical interactions between the human body and its environment is still unclear. The potential role of SR varies from load compensation and force enhancement via simple feedback control (Matthews, 1972, Stein and Thompson, 2006) to its effect on temporal organization of corticospinal circuits (Kilner et al., 2004). There are an increasing number of arguments to consider the role of SR in the recruitment of motor units at the level of the spinal motoneuron pool (Grimby and Hannerz, 1968, Scheppati et al., 1986, Garland and Miles, 1997, De Luca et al., 2009).
Although the functional role and origin of SR continue to be debated, TJ, the clinical equivalent of the phasic component of SR, is a very important component of a standard clinical examination. TJ is also known as tendon reflex or T-reflex. The amplitude of TJ is evaluated by a 5-point clinical scale (Hinderer and Dixon, 2001) that quantifies the movement of a body segment in response to a tap to the skin overlying the tendon of the muscle operating across the joint or distal portion of the body segment. The TJ score aids in the differential diagnosis of many neurological conditions; however, the score is not always associated with the functional status of patients. TJ inputs a non-physiological stimuli to the muscles (Matthews, 1990, Matthews, 2006, Stein and Thompson, 2006), but it remains unclear to what degree the kinematics generated during tendon tap exceed the ranges that muscles encounter in ADLs.
The development and refining of muscle imaging techniques (MRI, ultrasound) has opened a new avenue for studies of SR, allowing for measurement of muscle kinematics in vivo (Grubb et al., 1995). A combination of in vivo muscle measurement methods and standard reflex techniques may yield new insight into the potential biomechanical advantages of a system exhibiting reflexes. The first step in determining the advantages would be quantifying the biomechanical differences between the stretches experienced by muscles during the standard clinical TJ and those encountered by muscles during ADLs. A better understanding of these differences may help refine the clinical interpretation of this popular neurological test.
The muscle stretch receptors that are involved in the TJ are sensitive not only to the stretch amplitude and its velocity but also accelerations (Matthews, 1972). The sensitivity of some stretch receptors to acceleration was recently identified as functionally important especially during ADL (Dimitriou and Edin, 2008). In a preliminary study published in abstract form (Sikdar et al., 2009), we reported that muscle velocities during tendon jerk are in the ranges of those encountered by people in ADL. The previous analysis did not account for acceleration of the muscle generated by tendon tap.
The aim of this current study was to determine the range of angular knee kinematics (velocities and accelerations) corresponding to the muscle stretch elicited by TJ. This was achieved by measuring the longitudinal kinematics (velocities and accelerations) of the rectus femoris muscle in vivo using vector tissue Doppler imaging, an ultrasound-based method, and measuring knee angular kinematics in response to TJ with an electrogoniometer.
Section snippets
Materials and methods
Six (N = 6) healthy adult volunteers (3 men and 3 women; age = 24.5 ± 3 years) were recruited from the staff and students of George Mason University, Fairfax, VA, USA and provided informed, written consent. The exclusion criteria were previous diagnosis of neuromuscular disease or knee pathology or previous knee surgery. The Institutional Review Board of George Mason University, Fairfax, VA, USA approved the study protocol.
All subjects were asked to sit comfortably in an upright position. An
Results
The regression coefficients (mean ± std) between vp [cm s−1] and ωp [rad s−1]) were ωp = −0.09 (±0.53) + 0.526 (±0.31) vp. The ranges of the velocities and accelerations during maximum velocity knee flexion (Fig. 2) were 12 rad s−1 and 40 rad s−2 (cross-hatched area, Lebiedowska, 2008); and during drop jumps were 17.5 rad s−1 and 674.76 rad s−2, respectively (dotted area, Moran and Marshall, 2006). The estimated velocities calculated in our study ranged from 0.82 rad s−1 to 6.21 rad s−1 and they did not exceed the
Discussion
We found that during TJ, muscle elongation accelerations but not velocities exceed the range of values encountered during typical ADLs. Our study provides experimental evidence to support the non-physiological characteristics of tendon taps, which are often used during standard neurological exams (Matthews, 1990, Stein and Thompson, 2006).
The range of muscle lengthening velocities during TJ determined during our study agreed with the velocities measured by Grubb et al. (1995) (5.6 ± 1.3 cm s−1 to
Disclaimer
The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health.
Acknowledgements
This material is based in part upon work supported by the National Science Foundation under Grant No. 0953652 (PI: Siddhartha Sikdar).
References (25)
Oscillations in “brain–body–mind”—a holistic view including the autonomous system
Brain Res
(2008)- et al.
Cross-beam vector Doppler ultrasound for angle-independent velocity measurements
Ultrasound Med Biol
(2000) - et al.
Physiologic and clinical monitoring of spastic hypertonia
Phys Med Rehabil Clin N Am
(2001) The kinematic consequences of invariant dynamics in children 6 to 18 years of age
J Biomech
(2008)- et al.
Effects of contraction intensity on muscle fascicle and stretch reflex behavior in the human triceps surae
J Appl Physiol
(2008) - et al.
Motor unit recruitment and proprioceptive feedback decrease the common drive
J Neurophysiol
(2009) - et al.
Discharges in human muscle spindle afferents during a key-pressing task
J Physiol.
(2008) - et al.
The ‘late’ reflex responses to muscle stretch: the ‘resonance hypothesis’ versus the ‘long-loop hypothesis’
Physiol
(1982) - et al.
Experimental characterization of a vector Doppler system based on a clinical ultrasound scanner
Conf Proc IEEE Eng Med Biol Soc
(2009) - et al.
Control of motor units in human flexor digitorum profundus under different proprioceptive conditions
J Physiol
(1997)