Vestibular and somatosensory contributions to responses to head and body displacements in stance

The relative contribution of vestibular and somatosensory information to triggering postural responses to external body displacements may depend on the task and on the availability of sensory information in each system. To separate the contribution of vestibular and neck mechanisms to the stabilization of upright stance from that of lower body somatosensory mechanisms, responses to displacements of the head alone were compared with responses to displacements of the head and body, in both healthy subjects and in patients with profound bilateral vestibular loss. Head displacements were induced by translating two 1-kg weights suspended on either side of the head at the level of the mastoid bone, and body displacements were induced translating the support surface. Head displacements resulted in maximum forward and backward head accelerations similar to those resulting from body displacements, but were not accompanied by significant center of body mass, ankle, knee, or hip motions. We tested the effect of disrupting somatosensory information from the legs on postural responses to head or body displacements by sway-referencing the support surface. The subjects' eyes were closed during all testing to eliminate the effects of vision. Results showed that head displacements alone can trigger medium latency (48-84 ms) responses in the same leg and trunk muscles as body displacements. Nevertheless, it is unlikely that vestibular signals alone normally trigger directionally specific postural responses to support surface translations in standing humans because: (1) initial head accelerations resulting from body and head displacements were in opposite directions, but were associated with activation of the same leg and trunk postural muscles; (2) muscle responses to displacements of the head alone were only one third of the amplitude of responses to body displacements with equivalent maximum head accelerations; and (3) patients with profound bilateral vestibular loss showed patterns and latencies of leg and trunk muscle responses to body displacements similar to those of healthy subjects. Altering somatosensory information, by sway-referencing the support surface, increased the amplitude of ankle muscle activation to head displacements and reduced the amplitude of ankle muscle activation to body displacements, suggesting context-specific reweighting of vestibular and somatosensory inputs for posture. In contrast to responses to body displacements, responses to direct head displacements appear to depend upon a vestibulospinal trigger, since trunk and leg muscle responses to head displacements were absent in patients who had lost vestibular function as adults.(ABSTRACT TRUNCATED AT 400 WORDS)     

From balance regulation to body orientation: two goals for muscle proprioceptive information processing?

This study was based on the assumption that the central processing of proprioceptive inputs that arise from numerous muscles contributes to both awareness and control of body posture. The muscle-spindle inputs form a "proprioceptive chain" which functionally links the eye muscles to the foot muscles. Here, we focused on the specific contribution of two links in the control of human erect posture by investigating how proprioceptive messages arising from ankle and neck muscles may be integrated by the central nervous system. Single or combined mechanical vibrations were applied to different muscle tendons at either one (ankle or neck) or both (ankle plus neck) body levels. The amplitude and the specific direction of the resulting oriented body tilts were analyzed by recording the center of foot pressure (CoP) through a force platform with four strain gauges. The results can be summarized as follows: (1) the vibration-induced whole-body tilts were oriented according to the muscles stimulated; furthermore, the tilts were in opposite directions when neck or ankle muscles on the same side of the body were stimulated; (2) except for the ankle antagonist muscles, co-vibrating adjacent or antagonist muscles at the same body level (ankle or neck) resulted in body sways, whose orientation was a combination of those obtained by stimulating these muscles separately; and (3) likewise, co-vibrating ankle and neck muscles induced whole-body postural responses, whose direction and amplitude were a combination of those obtained by separate vibration. We conclude that the multiple proprioceptive inputs originating from either one or both body levels may be co-processed in terms of vector-addition laws. Moreover, we propose that proprioceptive information from ankle and neck muscles may be used for two tasks: balance control and body orientation, with central integration of both tasks.     

Recovery of stretch reflex responses following mechanical stimulation

The recovery behaviour of mechanically evoked stretch responses was investigated. Stimuli which promoted identical dorsiflexing movements around the ankle joint were applied to ten subjects in two positions, seated and upright. The experimental sets comprised single as well as double dorsiflexing displacements. In the latter the stimuli were elicited for durations of either 100, 200 or 400 ms. Stretch responses following the first displacements were related to the stretch velocity but not to the amplitude. The responses of the plantar flexors following the second mechanical dorsiflexion were reduced with respect to the delay time between the first and second displacement. In addition, the magnitudes of these responses depended on the functional task: the stretch responses recovered much faster in the standing position when the triceps surae muscle was only slightly activated, whereas in the relaxed sitting position the reflexes remained suppressed. Both reciprocal inhibition, as well as the time course of the reformation of intrafusal cross-bridge links, may help to explain the depression of the monosynaptic stretch reflex.     

Effects of varying acceleration of platform translation and toes-up rotations on the pattern and magnitude of balance reactions in humans

Different movement synergies used to restore balance in response to sudden support surface displacements have been described, which include the ankle movement synergy and a number of multisegmental movement synergies. The purpose of this study was to extend the analysis of the effects of stimulus magnitude on the pattern and scaling of balance reactions to larger magnitudes of balance disturbances, and to other types of balance disturbances, in particular, forward translations (FT), backward translations (BT), and toes-up rotations (RT). In addition, we examined whether the timing and magnitude of center of body mass (CM) displacement is an invariant feature of corrective responses to varying magnitudes of balance disturbances. Thirteen healthy adults were subjected to FT, BT, and RT of varying acceleration/velocity. The balance disturbance induced by FT and BT was fundamentally different from that induced by RT. The balance requirement during FT and BT was to rapidly translate the CM forward/backward to the new position within the displaced base of support. For RT, the requirement was to minimize the backward displacement of the CM. As evidenced from the initial phase of ankle, knee, and hip angular displacements and anterior-posterior (A-P) center of foot pressure displacement, the magnitude of the balance disturbance increased with increasing platform acceleration/velocity. For FT and BT, the present findings are consistent with the view that trajectory of CM is a control variable, as the timing, peak magnitude, and time to peak CM displacement did not vary as a function of platform acceleration/velocity. However, for RT, the peak magnitude and time to peak CM displacement did increase with increasing platform acceleration/velocity. The results demonstrate that in response to FT, BT, and RT, stability was restored by distinct multisegmental movement synergies. The corrective response to FT consisted of early knee flexion then ankle dorsiflexion and hip extension. The corrective response to BT consisted of hip flexion and ankle plantar flexion. For RT early hip flexion and knee flexion was observed. All muscles recorded (tibialis anterior, soleus, gastrocnemius, hamstrings, and quadriceps) were activated within a range of 60 to 170 ms from onset of platform displacement. For FT, BT, and RT, the pattern and timing of angular displacements and muscle responses did not vary as a function of platform acceleration/velocity, while there was a significant effect of platform acceleration/velocity on the magnitude of the corrective response, that is, peak magnitude of corrective hip, knee, and ankle angular displacements and magnitude of muscle responses. The present findings indicate that multiple sources of spatial information are necessary for the selection and initiation of the appropriate corrective response to meet the requirements of the different balance tasks. The present results strongly endorse the concept of a postural control network for recovery of standing balance, as opposed to positive feedback through local segmental or long loop reflex circuits.     

Effects of dorsolateral spinal lesions on stretch reflex threshold and stiffness in awake cats

Measurements of threshold angle and incremental dynamic stiffness (IDS) were derived from triceps surae stretch reflexes, elicited by ramp and hold flexion at the ankle joint of four cats that were tested while awake. Stretch reflexes were assessed from trials that began from different ankle joint start positions or were matched using a post-hoc analysis for initial background force during testing sessions before and following unilateral lesions of the dorsolateral funiculus at levels ranging from T13 to L3. Unilateral lesions of the dorsolateral funiculus (DLF) produced significant ipsilateral decreases in stretch reflex threshold and increases in reflex gain, measured as incremental dynamic stiffness (IDS). ANCOVA testing indicated that the reduction in threshold, but not the increase in IDS, was dependent upon the level of background force. Reflex testing from different start angles demonstrated that DLF lesions diminished the correlation between threshold and IDS. Intravenous infusion of ketamine dose-dependently reduced IDS, compared with testing in the unanaesthetized state. Postoperative reflex testing during infusion of ketamine at 22.2 mg/kg per h, when electromyographic responses were reduced to 24% of control levels, abolished differences in IDS between the ipsilateral and contralateral hindlimbs. These and related observations suggest that the postoperative increase in IDS in awake animals was not due to an increase in passive stiffness.     

Fiber architecture of the extensors of the hindlimb in semiterrestrial and arboreal guenons

Fiber architecture of the extensor musculature of the knee and ankle is examined in two African gueon species--the semiterrestrial Cercopithecus aethiops, and the arboreal C. ascanius. Using histologic and microscopic techniques to measure lengths of sarcomeres, the original lengths of muscle fasciculi and angles of pinnation in quadriceps femoris and triceps surae are reconstructed from direct measurements on cadavers. Calculations of reduced physiological cross-sectional area, mass/predicted effective tetanic tension, maximum excursion, and tendon length/fasciculus+tendon lengths are correlated to preferred locomotor modalities in the wild. For both species, greater morphological differences occur among the bellies of quadriceps femoris--rectus femoris, vastus intermedius, v. lateralis, and v. medialis--than among the bellies of triceps surae--gastrocnemius lateralis, g. medialis, plantaris, and soleus. With regard to quadriceps femoris, few differences occur between species. Interspecific differences in the triceps surae indicate (1) redirection of muscle force to accommodate arboreality in which the substrate is less than body width; (2) muscles more suited for velocity in the semiterrestrial vervets; and (3) muscles used more isotonically in vervets and more isometrically in red-tailed monkeys. The inherent flexibility of muscles may be preadaptive to a primary species shift in locomotor modality until the bony morphology is able to adapt through natural selection.     

Neuromuscular responses to disturbance of balance in children with prenatal exposure to alcohol

Alcohol-exposed children display delayed motor development and impaired fine- and gross-motor skills, including deficits in the maintenance of balance. In a recent study, we assessed the contribution of visual, somatosensory, and vestibular information to the ability to maintain balance. Our findings suggested that alcohol-exposed children were overly reliant on somatosensory information and were unable to compensate by using the visual and/or vestibular systems. To understand the nature of these observed balance deficits, corrective postural reactions were examined by exposing standing subjects to rapid toe-up movements of the support surface. Subjects for this study were alcohol-exposed (ALC) and normal control (NC) children matched for age and sex. Postural reactions were quantified by measuring electromyographic activity of the triceps surae and anterior tibialis muscles. Analyses revealed no differences between the ALC and NC groups on short- and medium-latency electromyographic responses, which are thought to be involuntary mono- and polysynaptic spinal reflexes, respectively. However, when compared with the NC group, the ALC group displayed increased long-latency responses, which are thought to involve a transcortical pathway. Although we are not able to rule out the possibility of additional peripheral (e.g., vestibular) disturbance as a contributing factor to postural instability, our findings suggest that the balance deficits seen in alcohol-exposed children are, at least in part, central in nature.     

The effect of flumazenil on CNS oxygen toxicity in the rat

The effect of afferent cutaneous electrical stimulation on the spasticity of leg muscles was studied in 20 patients with chronic hemiplegia after stroke. Stimulation electrodes were placed over the sural nerve of the affected limb. The standard method of cutaneous stimulation, TENS with impulse frequency of 100 Hz, was applied. The tonus of the leg muscles was measured by means of an electrohydraulic measuring brace. The EMG stretch reflex activity of the tibialis anterior and triceps surae muscles was detected by surface electrodes and recorded simultaneously with the measured biomechanical parameters. In 18 out of 20 patients, a mild but statistically significant decrease in resistive torques at all frequencies of passive ankle movements was recorded following 20 min of TENS application. The decrease in resistive torque was often (but not always) accompanied by a decrease in reflex EMG activity. This effect of TENS persisted up to 45 min after the end of TENS. The results of the study support the hypothesis that TENS applied to the sural nerve may induce short-term post-stimulation inhibitory effects on the abnormally enhanced stretch reflex activity in spasticity of cerebral origin.     

Managing equinus in children with cerebral palsy: electrical stimulation to strengthen the triceps surae muscle

A new therapeutic proposal for the management of equinus in children with cerebral palsy is to strengthen the calf muscles instead of weakening them surgically. Prior research indicates that in children with cerebral palsy the triceps surae muscle is weak and needs strengthening. Neuromuscular electrical stimulation (NMES) was used as an adjunct to physical therapy. A portable NMES unit with a hand-held remote switch stimulated an active muscle gait cycle. Results are discussed for four children, who showed improved gait, balance, posture, active and passive ankle range of motion, and foot alignment. The toe walkers became plantigrade and the equinovalgus posture of the foot decreased. Spasticity did not increase.     

Myogenic vestibular-evoked potentials in normal subjects: a comparison between responses obtained from sternomastoid and trapezius muscles

Brief intense clicks cause short latency microcontraction of cervical muscles. Several studies have supported the hypothesis that these microcontractions are of vestibular origin. Averaging these muscular responses enables us to obtain myogenic vestibular evoked potential (MVEP). The receptor of these responses is thought to be the saccule, afferent pathways being the vestibular nerve and efferent pathways the vestibulospinal tract. However, discrepancies are reported with regard to results obtained in healthy subjects: some authors obtained symmetrical response to monaural clicks whereas others obtained responses of greater amplitude on the muscle ispilateral to stimulation. These discrepancies may be due to the presence of different recording sites (inion, sternomastoid or trapezius muscles). The aim of this study was to clarify MVEP results in healthy subjects, using a simple non-traumatic method, and to compare the results obtained on sternomastoid (SM) and trapezius muscles (TRP). Sixteen normal hearing healthy subjects were involved. Latencies and amplitude of both SM and TRP muscle were reproducible in the same subject. Patterns of response were similar to those obtained in previous studies. Following binaural and monaural stimulations, latencies of MVEP were symmetrical on both muscles and amplitudes tended to be greater on muscles contralateral to stimulation, which conflicts with previous results in the literature. Whatever the type of stimulation, latencies of responses obtained on SM were significantly shorter (mean = -3.8 ms), and amplitudes lower (mean = -7.1 microV), than those obtained on TRP. Binaural stimulation resulted in responses of greater amplitude compared to monaural (mean = 0.45 microV). Given the intrasubject reproducibility of the responses, these methods allow MEVP to be recorded in a standardized and reproducible way.     

The role of weakness of triceps surae muscles in astasia without abasia

OBJECTIVE: To investigate the role of weakness of the bilateral triceps surae muscles-the gastrocnemius and soleus muscles-in astasia without abasia and whether compensating for muscle weakness with ankle-foot orthoses improves this disability. DESIGN: Case-control study of clinical findings and before and after trial of ankle-foot orthoses. SETTING: Clinics of the departments of rehabilitation medicine of two university hospitals. PATIENTS: A stilts group consisting of 23 patients with astasia without abasia, and a non-stilts group without this phenomenon consisting of 12 patients with hereditary motor sensory neuropathy, 15 patients with lumbosacral spondylotic radiculopathy or spondylolisthesis, and 20 healthy volunteers. MAIN OUTCOME MEASURE: Clinical findings of the stilts and non-stilts groups were compared and the sensitivity and specificity of each clinical finding was calculated. The length of the centre of foot pressure (COP) while standing was measured in a bilateral below knee amputee and 16 consecutive patients in the stilts group with and without ankle-foot orthoses. RESULTS: Weakness of the triceps surae muscles was the only finding that differed significantly between the two groups and was both sensitive and specific. The amputee was unable to stand in place without dorsiflexion bumpers, which functioned similarly to the triceps surae muscle. Bilateral ankle-foot orthoses improved the COPs of 14 out of 16 patients. CONCLUSION: The main cause of astasia without abasia is weakness of the triceps surae muscles, and this disability is improved by bilateral ankle-foot orthoses.     

Inefficient postural responses to unexpected slips during walking in older adults

BACKGROUND: Slips account for a high percentage of falls and subsequent injuries in community-dwelling older adults but not in young adults. This phenomenon suggests that although active and healthy older adults preserve a mobility level comparable to that of young adults, these older adults may have difficulty generating efficient reactive postural responses when they slip. This study tested the hypothesis that active and healthy older adults use a less effective reactive balance strategy than young adults when experiencing an unexpected forward slip occurring at heel strike during walking. This less effective balance strategy would be manifested by slower and smaller postural responses, altered temporal and spatial organization of the postural responses, and greater upper trunk instability after the slip. METHODS: Thirty-three young adults (age range=19-34 yrs, mean=25+/-4 yrs) and 32 community-dwelling older adults (age range=70-87 yrs, mean=74+/-14 yrs) participated. Subjects walked across a movable forceplate which simulated a forward slip at heel strike. Surface electromyography was recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data were collected from the right (perturbed) side of the body. RESULTS: Although the predominant postural muscles and the activation sequence of these muscles were similar between the two age groups, the postural responses of older adults were of longer onset latencies, smaller magnitudes, and longer burst durations compared to young adults. Older adults also showed a longer coactivation duration for the ankle, knee, and trunk agonist/antagonist pairs on the perturbed side and for the knee agonist/antagonist pair on the nonperturbed side. Behaviorally, older adults became less stable after the slips. This was manifested by a higher incidence of being tripped (21 trials in older vs 5 trials in young adults) and a greater trunk hyperextension with respect to young adults. Large arm elevation was frequently used by older adults to assist in maintaining trunk stability. In an attempt to quickly reestablish the base of support after the slips, older adults had an earlier contralateral foot strike and shortened stride length. CONCLUSION: The combination of slower onset and smaller magnitude of postural responses to slips in older adults resulted in an inefficient balance strategy. Older adults needed secondary compensatory adjustments, including a lengthened response duration and the use of the arms, to fully regain balance and prevent a fall. The shorter stride length and earlier contralateral foot strike following the slip indicate use of a more conservative balance strategy in older adults.     

Proximal rupture in the triceps surae a typical, but often unrecognized injury

An account is given of 12 high ruptures of the triceps surae, a traumatic lesion of the medial belly of the gastrocnemius, caused by sudden overstreching of the muscle by concomitant ankle dorsiflexion and full knee extension. In all cases the authors found characteristic clinical features. Surgical exploration in 5 of 12 cases verified the ruptures of the musculotendinous junction of the medial gastrocnemius belly. A follow-up study of 2 years showed that the surgical treatment seems to be better, especially in younger and athletic patients.     

Adapting reflexes controlling the human posture

Doubt about the role of stretch reflexes in movement and posture control has remained in part because the questions of reflex "usefulness" and the postural "set" have not been adequately considered in the design of experimental paradigms. The intent of this study was to discover the stabilizing role of stretch reflexes acting upon the ankle musculature while human subjects performed stance tasks requiring several different postural "sets". Task specific differences of reflex function were investigated by experiments in which the role of stretch reflexes to stabilize sway doing stance could be altered to be useful, of no use, or inappropriate. Because the system has available a number of alternate inputs to posture (e.g., vestibular and visual), stretch reflex responses were in themselves not necessary to prevent a loss of balance. Nevertheless, 5 out of 12 subjects in this study used long-latency (120 msec) stretch reflexes to help reduce postural sway. Following an unexpected change in the usefulness of stretch reflexes, the 5 subjects progressively altered reflex gain during the succeeding 3-5 trials. Adaptive changes in gain were always in the sense to reduce sway, and therefore could be attenuating or facilitating the reflex response. Comparing subjects using the reflex with those not during so, stretch reflex control resulted in less swaying when the task conditions were unchanging. However, the 5 subjects using reflex controls oftentimes swayed more during the first 3-5 trials after a change, when inappropriate responses were elicited. Four patients with clinically diagnosed cerebellar deficits were studied briefly. Among the stance tasks, their performance was similar to normal in some and significantly poorer in others. Their most significant deficit appeared to be the inability to adapt long-latency reflex gain following changes in the stance task. The study concludes with a discussion of the role of stretch reflexes within a hierarchy of controls ranging from muscle stiffness up to centrally initiated responses.     

Polysynaptic neuronal pathways from group I and group II afferents innervating tail muscles to hindlimb motoneurons in the cat

Postsynaptic potentials evoked in motoneurons innervating m. posterior biceps and semitendinosus (PBSt) and m. triceps surae (GS) by low threshold afferents from various tail muscles located at the level of the second-third caudal vertebrae were investigated in the non-anesthetized and spinalized cat. Afferent inputs from tail muscles on both sides predominantly evoked depolarizing potential in PBSt motoneurons and hyperpolarizing potential in GS motoneurons. The findings suggest that in general, tail muscle afferents facilitate flexor and inhibit extensor hindlimb motoneurons through polysynaptic pathways, so that the pelvic girdle is kept in a low position to maintain the stability of the body irrespective of different movements or posture of the tail.     

Gait pattern in the early recovery period after stroke

The gait patterns of eighteen patients who had had a single infarct due to obstruction of the middle cerebral artery were evaluated within one week after the patients had resumed independent walking and before a gait rehabilitation program had been initiated. Gait was analyzed with use of motion analysis, force-plate recordings, and dynamic surface electromyographic studies of the muscles of the lower extremities. The patterns of motion of the lower extremity on the hemiplegic side had a stronger association with the clinical severity of muscle weakness than with the degree of spasticity, balance control, or phasic muscle activity. There was a delay in the initiation of flexion of the hip during the pre-swing phase, and flexion of the hip and knee as well as dorsiflexion of the ankle progressed only slightly during the swing phase. During the stance phase, there was decreased extension of the hip that was related to decreased muscle effort and a coupling between flexion of the knee and dorsiflexion of the ankle. The abnormal patterns of motion altered the velocity, the length of the stride, the cadence, and all phases of the gait cycle. The duration of the pre-swing phase was prolonged for the patients who had the slowest gait velocities. There also were abnormal movements of the upper extremity, the trunk, the pelvis, and the lower extremity on the unaffected side in an effort to compensate for the decreased velocity on the hemiplegic side. As velocity improved, these abnormal movements decreased. Therefore, the goal of therapy should be to improve muscle strength and coordination on the hemiplegic side, especially during the pre-swing phase.     

Control of torque direction by spinal pathways at the cat ankle joint

To study the biomechanics of the calcaneal tendon's complex insertion onto the calcaneus, we measured torque-time trajectories exerted by the triceps surae and tibialis anterior muscles in eight unanesthetized decerebrate cats using a multi-axis force-moment sensor placed at the ankle joint. The ankle was constrained to an angle of 110 degrees plantarflexion. Muscles were activated using crossed-extension (XER), flexion (FWR), and caudal cutaneous sural nerve (SNR) reflexes. Torque contributions of other muscles activated by these reflexes were eliminated by denervation or tenotomy. In two animals, miniature pressure transducers were implanted among tendon fibers from the lateral gastrocnemius (LG) muscle that insert straight into the calcaneus or among tendon fibers from the medial gastrocnemius (MG) that cross over and insert on the lateral aspect of calcaneus. Reflexively evoked torques had the following directions: FWR, dorsiflexion and adduction; SNR, plantarflexion and abduction; and XER, plantarflexion and modest abduction or adduction. The proportion of abduction torque to plantarflexion torque was always greater for SNR than XER; this difference was about 50% of the magnitude of abduction torque generated by tetanic stimulation of the peronei. During SNR, pressures were higher in regions of the calcaneal tendon originating from MG than regions originating from LG. Similarly, pressures within the MG portion of the calcaneal tendon were higher during SNR than during XER, although these two reflexes produced matched ankle plantarflexion forces. Selective tenotomies and electromyographic recordings further demonstrated that MG generated most of the torque in response to SNR, while soleus, LG, and MG all generated torques in response to XER.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cutaneous reflexes during human gait: electromyographic and kinematic responses to electrical stimulation

The functions of ipsilateral cutaneous reflexes were studied with short trains of stimuli presented pseudorandomly to the superficial peroneal (SP) and tibial nerves during human gait. Electromyograms (EMGs) of tibialis anterior (TA), soleus, lateral and medial gastrocnemius, vastus lateralis (VL), and biceps femoris (BF) muscle were recorded, together with ankle and knee joint angles. Net reflex EMG responses were quantified in each of the 16 parts of the step cycle according to a recently developed technique. After SP nerve stimulation, TA muscle showed a significant suppression during swing phase that was highly correlated to ankle plantarflexion. BF and VL muscles were both excited throughout swing and significantly correlated to knee flexion during early swing. Tibial nerve stimulation caused dorsiflexion during late stance, but plantarflexion during late swing. We argue that SP nerve reflexes are indicative of a stumbling corrective response to nonnoxious electrical stimulation in humans. The correlated kinematic responses after tibial nerve stimulation may allow smooth movement of the swing leg so as to prevent tripping during swing and to assist placing and weight acceptance at the beginning of stance.     

Cerebrospinal fluid protein changes in multiple sclerosis after dental amalgam removal

To date, limited information exists describing a relatively new stretching technique, dynamic range of motion (DROM). The purpose of this study was to compare the effects of DROM with static stretch on hamstring flexibility. Fifty-eight subjects, ranging in age from 21 to 41 years and with limited hamstring flexibility (defined as 30 degrees loss of knee extension measured with the femur held at 90 degrees of hip flexion), were randomly assigned to one of three groups. One group performed DROM 5 days a week by lying supine with the hip held in 90 degrees of flexion. The subject then actively moved the leg into knee extension (5 seconds), held the leg in end range knee extension for 5 seconds, and then slowly lowered the leg to the initial position (5 seconds). These movements were performed six times per session (30 seconds of total actual stretching time). The second group performed one 30-second static stretch, 5 days per week. The third group served as a control group and did not stretch. Before and after 6 weeks of training, flexibility of the hamstring muscles was determined in all three groups by measuring knee extension range of motion (ROM) with the femur maintained in 90 degrees of hip flexion. Data were analyzed with a 2 x 3 (test x group) two-way analysis of variance (ANOVA) with repeated measures on one variable (test) and appropriate post hoc analyses. The results of the two-way ANOVA revealed a significant interaction. Further statistical post hoc analysis of data to interpret the interaction revealed significant differences between the control group (gain = 0.70 degree) and both stretching groups, as well as a significant difference between the static stretch group (gain = 11.42 degrees) and the DROM group (gain = 4.26 degrees). The results of this study suggest that, although both static stretch and DROM will increase hamstring flexibility, a 30-second static stretch was more effective than the newer technique, DROM, for enhancing flexibility. Given the fact that a 30-second static stretch increased ROM more than two times that of DROM, the use of DROM to increase flexibility of muscle must be questioned.