Machine-learning models utilizing CYP3A4*1G show improved prediction of hypoglycemic medication in Type 2 diabetes.

The effectiveness and side effects of Type 2 diabetes (T2D) medication are related to individual genetic background. SNPs CYP3A4 and CYP2C19 were introduced to machine-learning models to improve the performance of T2D medication prediction. Two multilabel classification models, ML-KNN and WRank-SVM, trained with clinical data and CYP3A4/CYP2C19 SNPs were evaluated. Prediction performance was evaluated with Hamming loss, one-error, coverage, ranking loss and average precision. The average precision of ML-KNN and WRank-SVM using clinical data was 92.74% and 92.9%, respectively. Combined with CYP2C19*2*3, the average precision dropped to 88.84% and 89.93%, respectively. While combined with CYP3A4*1G, the average precision was enhanced to 97.96% and 97.82%, respectively. Results suggest that CYP3A4*1G can improve the performance of ML-KNN and WRank-SVM models in predicting T2D medication performance.

About 10% of adults around the world are living with Type 2 Diabetes (T2D). Due to the huge number of patients and the complexity of individual makeup, it is a challenge for doctors to prescribe appropriate hypoglycemic drugs. To aid prescribing, machine-learning models were developed to predict medication schemes based on patients' demographic information and laboratory test results. These models treat prediction as a multilabel classification problem, with each class of medication as a label. This work was designed to determine whether the introduction of genetic information would improve prediction performance. The machine-learning models were trained using datasets with and without genetic information and their performance was compared. The performance of the machine-learning models was improved by incorporating the SNP CYP3A4*1G into the datasets. Thus, this work demonstrates a novel strategy to improve the prediction of T2D hypoglycemic medication performance and provides new ideas for how to support the T2D health system with machine-learning techniques.

The Impacts of the COVID-19 Pandemic on Doctor of Physical Therapy Students: A National Survey.

INTRODUCTION: Since the lockdown in March 2020, the COVID-19 pandemic has inevitably affected all individuals across the world. The purpose of this study was to determine the perceived impacts of the pandemic on doctor of physical therapy (DPT) students and if there were any statistically significant differences based on minority status, gender, or class standing. REVIEW OF LITERATURE: Literature suggested that DPT students experienced negative impacts of the pandemic on academic success and mental health. However, there is a lack of comprehensive understanding of the perceived physical, mental, financial, and academic impacts of the COVID-19 pandemic by physical therapist students nationally. SUBJECTS: Convenience sampling was used to recruit all students enrolled in physical therapist programs in the United States. METHODS: The research design was a cross-sectional survey administered electronically using the Alchemer survey platform with 12 Likert scale items compiled in the physical, mental, financial, and academic domains. All items were designed to evaluate the perceived impacts of the pandemic on a 5-point scale from 1 (strongly disagree) to 5 (strongly agree). RESULTS: A total of 1,230 completed responses were received. The mean responses were 3.45 (SD 1.12), 3.48 (SD 0.92), 2.74 (SD 1.03), and 3.33 (SD 0.93) for the physical, mental, financial, and academic domains, respectively. No significant difference was found based on minority status. A statistically significant difference was found in the mental domain, with female students perceiving a more negative impact by the pandemic. First-year students reported a significantly higher negative impact in the physical domain compared with second-year students. The perceived impact in the academic domain was significantly higher for both first- and second-year students than third-year students. CONCLUSIONS: Developing and promoting access to campus and community resources to address the challenges caused by the COVID-19 pandemic is critical to facilitating student success during and after the pandemic.

Measuring Cervical Rotation During Telehealth.

INTRODUCTION: Measuring cervical rotation virtually can be challenging during telehealth. The objective of this study was to proof the concept of measuring cervical rotation virtually during telehealth. METHODS: Subjects were instructed to sit in a chair with back supported and face to a computer with video conferencing platform communicating remotely with another computer. The subjects were instructed to rotate their neck from 0 to the end range with increments of 10 . Cervical rotation (CRoM) was calculated based on the changes of the distance between the subject's eyes on the screenshot. Data analysis included descriptive analysis, Pearson correlation, and Bland-Altman analysis. RESULTS: The mean CRoM was 0.0 (SD 0.0), 14.3 (3.4), 28.5 (5.1), 39.9 (5.9), 49.2 (6.5), 57.7 (6.8), 65.5 (6.9), 72.6 (5.5), and 80.8 (3.7 ) from 0 to 80 in 10 increments, respectively. Pearson correlation coefficient (r) was 0.99, indicating a very high correlation. The Bland-Altman analysis revealed that 91.7% (111 out of 121) of the CRoM fell within the limits of agreement (95% confidence interval). DISCUSSION: Cervical rotation can be measured virtually using the changes of the distance between subject's eyes. No additional devices are required so it would work well for most patients.

A Randomized Controlled Trial of Power Posing on Timed Up and Go Test.

BACKGROUND: Integrating psychological principles into physical therapy treatment may enhance patient outcomes. One intervention strategy from psychological perspectives that could be integrated in physical therapy practice is power posing. There is a lack of research on the effects of power posing on functional outcomes commonly used in physical therapy. OBJECTIVE: To determine the effects of power posing on the timed up and go test score. DESIGN: Randomized controlled trial. METHODS: Subjects in the experimental group were instructed to stand with hands on their hips, elbows pointing out and feet approximately 1 foot apart for 20 s. Subjects in the control group were instructed to stand with hands and arms wrapping around the torso and feet together for 20 s. Timed up and go test was administered using an OmniVR Virtual Rehabilitation System before and after the postural intervention. RESULTS: The timed up and go test score changed by -0.17 s (SD 0.65) and -0.20 s (SD 0.43) for the experimental and control groups, respectively (p=0.87). CONCLUSIONS: The timed up and go test scores for both experimental and control groups improved slightly. However, the results did not show significant effects of power posing in the timed up and go test scores.

Severe Pain in Veteran Students.

BACKGROUND: Severe pain is prevalent in military veterans. Veteran students face significant challenges in attaining academic success. Understanding the impact of pain on learning of veteran students is very important to better advocate for veteran students and promote social responsibility and cultural competence. OBJECTIVE: The objective of the research was to determine pain in veteran students compared to nonveteran students. DESIGN: The research design was a cross-sectional non-experimental survey. METHODS: The survey included a total of 6 questions adapted from the National Health Interview Survey and was administered using SurveyGizmo. RESULTS: Veteran students are 4.3 times more likely to report severe pain than nonveteran students. 98.6% veteran students reported pain and 22.2% had severe pain. 25.0% of veteran students reported the ability to carry out daily work limited by pain. Only 4.2% of veteran students reported sufficient resources on campus helping them deal with pain, while 58.3% reported sufficient resources off campus. CONCLUSIONS: Veteran students had statistically significantly more severe pain. They were more limited by pain in carrying out daily work and reported fewer resources to help them cope with pain. The data can inform strategies for advocacy activities of physical therapists and assessment for culturally competent education.

Noncontact Measurement of the Deformation of Sternal Skin During Shoulder Movements and Upper Extremity Activities Restricted by Sternal Precautions.

Background: Existing variation has been identified in the rehabilitation programs for patients following cardiac surgery. Sternal precautions are believed to be overly restrictive and detrimental to patient recovery both physically and psychologically. Objective: The objective of this study was to determine the deformation of sternal skin during shoulder movements and upper extremity activities using a noncontact approach. Design: This was a cross-sectional, nonexperimental observational study. Methods: Two black dots were marked on participants' skin overlying sternoclavicular joints using an erasable marker. The coordinates of the dots were recorded using a digital camera and obtained using ImageJ, a public domain image processing program. Skin deformation between the 2 dots was quantified as biomechanical strain. Results: The sternal skin strain was - 15.3% (SD = 5.6) and - 12.0% (SD = 7.0) at 90 and 180 degrees of flexion; 0.0% (SD=0.0) and-12.8% (SD=5.8) at 90 and 180 degrees of abduction; and - 6.4% (SD=2.8), - 8.9% (SD=3.8), and - 9.8% (SD=4.6) when lifting the 0-, 5-, and 10-lb weights, respectively. The sternal skin strain was 7.9% (SD=3.9) for extension to the end range and-2.5% (SD=5.8) for pushing up from a chair. There is a trend of strain magnitude decrease with the increase of rhomboid strength, but no statistically significant association was found between them (R=0.12). Limitations: Limitations included convenience sampling, small sample size, and using skin deformation as a proxy for mechanical loading of the bony structures. Conclusions: The data do not support the restriction on most of the shoulder movements and upper extremity activities following cardiac surgery. The approach has the advantage of measuring skin deformation in the entire sternal region.

Meeting the Challenge of Instructor Shortages: A Blended Teaching and Learning Model for a Neuroscience Course in a Doctor of Physical Therapy Program.

BACKGROUND: Physical therapy workforce shortages are expected to increase for all 50 states through 2030. There is a recognized nationwide unprecedented shortage of well-prepared physical therapy instructors. One practical solution can be to share instructors among Doctor of Physical Therapy (DPT) programs using a blended teaching and learning model. OBJECTIVE: The purpose of this project was to evaluate the effectiveness of a blended teaching and learning model for a neuroscience course in a DPT program. METHODS: Faculty members from two DPT programs collaborated to develop, implement, and evaluate a blended teaching and learning model. The Blackboard Learning Management System (LMS) was available at both institutions and chosen as the learning platform. The design of this research study was retrospective nonexperimental observational. RESULTS: The overall feedback from the students was positive. Most students (91.6%) strongly agreed or agreed that the content of the course was appropriate for learning neuroscience. The students taking this blended course performed slightly better than the students taking the traditional course, though there was no significant difference (p=0.06). CONCLUSIONS: The results support the use of a blended teaching and learning model to meet faculty shortage challenges. Future research with a larger sample size is necessary.

Controversial Issues in Healthcare Policy: A Survey of Doctor of Physical Therapy Students in a Public University.

BACKGROUND: The recently passed legislation and proposed policy changes governing the healthcare system have been met with extensive debate and controversy. OBJECTIVE: The primary objective of the study was to determine the attitudes of Doctor of Physical Therapy (DPT) students towards some of these controversial issues. The secondary objective was to determine the demographic factors, including number of years in a physical therapy program, that contribute to their attitude formation. METHODS: The research design was a cross-sectional non-experimental survey. Purposive sampling was used to recruit subjects in a public university. Subjects took the survey including nine Likert scale questions/statements on controversial issues inspired from legislative efforts and news media sources and one open-ended question. RESULTS: Of the 111 recruited, 106 students agreed to participate as subjects and completed the survey. Only 18.9% agreed or strongly agreed that the Patient Protection and Affordable Care Act is a positive solution for the healthcare system in America. Political affiliation, class level, and developmental environment were associated with a few questions/statements. CONCLUSIONS: DPT students in the sample had very diverse attitudes towards controversial issues in healthcare policy. Some of these attitudes revealed very different paradigms from the results found among medical students and the general public.

Acupressure for chronic low back pain: a single system study.

[Purpose] Low back pain (LBP) is the leading cause of global disability. Acupressure is a manual approach that can be used for self-management of LBP. The purpose of the study was to determine the effectiveness of acupressure in treating chronic LBP. [Subjects and Methods] The research design was a single system study utilizing an AB design. The subject was recruited using convenience sampling. During phase A, the subject received traditional physical therapy interventions. During phase B, the subject received acupressure in addition to traditional physical therapy interventions. Outcomes included the Visual Analog Scale (VAS), the Patient Specific Functional Scale (PSFS), and the Oswestry Disability Index (ODI). [Results] For the VAS, the pain was 38.8 mm at baseline, decreased to 11.3 mm after phase A, and decreased to 2.5 mm after phase B. For the PSFS, the subject's function was 5/10 at baseline, remained the same after phase A, and increased to 9/10 after phase B. For the ODI, the subject's disability was moderate (30%) at the baseline, decreased to minimal (14%) after phase A, and completely resolved (0%) after phase B. [Conclusion] The data indicated that integrating acupressure in physical therapy could reduce pain, increase function, and decrease disability.

Dry cupping for plantar fasciitis: a randomized controlled trial.

[Purpose] The purpose of this study was to determine the effects of dry cupping on pain and function of patients with plantar fasciitis. [Subjects and Methods] Twenty-nine subjects (age 15 to 59 years old, 20 females and 9 males), randomly assigned into the two groups (dry cupping therapy and electrical stimulation therapy groups), participated in this study. The research design was a randomized controlled trial (RCT). Treatments were provided to the subjects twice a week for 4 weeks. Outcome measurements included the Visual Analogue Pain Scale (VAS) (at rest, first in the morning, and with activities), the Foot and Ankle Ability Measure (FAAM), the Lower Extremity Functional Scale (LEFS), as well as the pressure pain threshold. [Results]The data indicated that both dry cupping therapy and electrical stimulation therapy could reduce pain and increase function significantly in the population tested, as all the 95% Confidence Intervals (CIs) did not include 0 except for the pressure pain threshold. There was no significant difference between the dry cupping therapy and electrical stimulation groups in all the outcome measurements. [Conclusion] These results support that both dry cupping therapy and electrical stimulation therapy could reduce pain and increase function in the population tested.

A quasi-experimental study on the effects of instrument assisted soft tissue mobilization on mechanosensitive neurons.

[Purpose] Instrument Assisted Soft Tissue Mobilization (IASTM) is a form of manual therapy. Despite its growing popularity and an increasing number of patients receiving IASTM each year, there is a lack of high-level evidence to elucidate its therapeutic mechanisms and to support its clinical applications. The purpose of this research project was to determine the effects of IASTM on activities of mechanosensitive neurons in skin. [Subjects and Methods] Twenty-three subjects, 9 females and 14 males, mean age 25.7 (SD 6.4) years old were recruited through a convenience sampling on the university campus. The study design was a quasi-experimental study using single group pretest-posttest design. The activities of mechanosensitive neurons were measured before and after the application of IASTM. [Results] The mean 2-point discrimination was 40.2 (SD 9.4) mm before IASTM and increased to 44.9 (SD 12.0) mm after IASTM. The increase was statistically significant pre and post IASTM. The mean pain threshold was 18.2 (SD 6.6) lb and increased slightly to 18.7 (SD 6.8) lb after IASTM; however, no statistical significance was found pre and post IASTM. [Conclusion] The data indicates that IASTM changes the neural activities in 2-point discrimination but not in pain threshold.

Should high-power posing be integrated in physical therapy?

[Purpose] Postural assessment and correction is a common approach in patient management to decrease symptoms and improve function for patients. The purpose of this study was to determine the effects of high-power posing on muscle strength and pain threshold. [Subjects and Methods] Thirty-one subjects, 16 females and 15 males, mean age 28.9 (SD 10.8) years old, were recruited through a convenience sampling on the university campus. The research design was a randomized controlled trial. In the experimental group, the subjects were instructed to stand in a high-power posture. In the control group, the subjects were instructed to stand in a low-power posture. Grip strength and pain threshold measurements were conducted before and after the postural intervention. [Results] The grip strength changed by -3.4 (-3.7, 0.3) % and 1.7 (-3.6, 5.3) % for the experimental and control groups, respectively. The pain threshold changed by 0.6 (-9.9, 10.4) % and 15.1 (-9.3, 24.4) % for the experimental and control groups, respectively. However, both changes were not significant as all the 95% CIs included 0. [Conclusions] The data did not show significant benefits of high-power posing in increasing grip strength and pain threshold compared to low-power posing.

Skin deformation during shoulder movements and upper extremity activities.

BACKGROUND: The necessity of sternal precautions for patients following cardiac surgery with median sternotomy has been questioned by clinicians, researchers, and even patients. The primary purpose was to determine if sternal skin deformation during shoulder movements and upper extremity activities is compressive or distractive and if there are any significant differences between the skin deformation at different positions during shoulder movements and upper extremity activities. The secondary purpose was to determine if sternal skin deformation is correlated with scapular stabilizer muscle strength. METHODS: The research design was a cross-sectional non-experimental descriptive study. A 3D electromagnetic tracking system was used to measure sternal skin deformation quantified by strain. FINDINGS: The sternal skin strain was -10.8 (SD 6.2) % and -9.8 (SD 6.1) % at 90 and 180° flexion (P=0.45), -2.7 (SD 3.4) % and -10.4 (SD 7.9) % at 90 and 180° abduction (P<0.01), -3.6 (SD 4.1) %, -4.9 (SD 6.4) %, and -6.8 (SD 5.2) % when lifting 0, 5, and 10lb weights (P=0.07), 0.7 (SD 2.5) % for extension, and -1.1 (SD 5.0) % for pushing up from a chair. There is a trend of strain magnitude decrease with the increase of rhomboid strength without significant association (R=0.14). INTERPRETATION: Our data does not support the restriction for most of the shoulder movements and upper extremity activities following cardiac surgery. The only exception is bilateral shoulder extension. We propose a strategy for preoperative physical therapy to stabilize scapular muscles to decrease mechanical loading translated from shoulder to sternum.

Using vertebral movement and intact paraspinal muscles to determine the distribution of intrafusal fiber innervation of muscle spindle afferents in the anesthetized cat.

Increasing our knowledge regarding intrafusal fiber distribution and physiology of paraspinal proprioceptors may provide key insights regarding proprioceptive deficits in trunk control associated with low back pain and lead to more effective clinical intervention. The use of vertebral movement as a means to reliably stretch paraspinal muscles would greatly facilitate physiological study of paraspinal muscle proprioceptors where muscle tendon isolation is either very difficult or impossible. The effects of succinylcholine (SCh) on 194 muscle spindle afferents from lumbar longissimus or multifidus muscles in response to computer-controlled, ramp-and-hold movements of the L(6) vertebra were investigated in anesthetized cats. Paraspinal muscles were stretched by moving the L(6) vertebra 1.5-1.7 mm in the dorsal-ventral direction. Initial frequency (IF), dynamic difference (DD), their changes (∆) following SCh injection (100-400 µg kg(-1)), and post-SCh dynamic difference (SChDD) were measured. Muscle spindle intrafusal fiber terminations were classified as primary or secondary fibers as well as bag(1) (b(1)c), bag(2) (b(2)c), b(1)b(2)c, or chain (c) fibers. Intrafusal fiber subpopulations were distinguished using logarithmic transformation of SChDD and ∆IF distributions as established by previous investigators. Increases in DD indicate strength of b(1)c influence while increases in IF indicate strength of b(2)c influence. Out of 194 afferents, 46.9 % of afferents terminated on b(2)c fibers, 46.4 % on b(1)b(2)c fibers, 1 % on b(1)c fibers, and 5.7 % terminated on c fibers. Based on these intrafusal fiber subpopulation distributions, controlled vertebral movement can effectively substitute for direct tendon stretch and allow further investigation of paraspinal proprioceptors in this anatomically complex body region.

The decreased responsiveness of lumbar muscle spindles to a prior history of spinal muscle lengthening is graded with the magnitude of change in vertebral position.

In the lumbar spine, muscle spindle responsiveness is affected by the duration and direction of a lumbar vertebra's positional history. The purpose of the present study was to determine the relationship between changes in the magnitude of a lumbar vertebra's positional history and the responsiveness of lumbar muscle spindles to a subsequent vertebral position and subsequent vertebral movement. Neural activity from multifidus and longissimus muscle spindle afferents in deeply anesthetized cats was recorded while creating positional histories of the L(6) vertebra. History was induced using a displacement-controlled feedback motor. It held the L(6) vertebra for 4 s at an intermediate position (hold-intermediate at 0 mm) and at seven positions from 0.07 to 1.55 mm more ventralward and dorsalward which lengthened (hold-long) and shortened (hold-short) the lumbar muscles. Following the conditioning hold positions, L(6) was returned to the intermediate position. Muscle spindle discharge at this position and during a lengthening movement was compared between hold-intermediate and hold-short conditionings and between hold-intermediate and hold-short conditionings. We found that regardless of conditioning magnitude, the seven shortening magnitudes similarly increased muscle spindle responsiveness to both vertebral position and movement. In contrast, the seven lengthening magnitudes produced a graded decrease in responsiveness to both position and movement. The decrease to position became maximal following conditioning magnitudes of ∼0.75 mm. The decrease to movement did not reach a maximum even with conditioning magnitudes of ∼1.55 mm. The data suggest that the fidelity of proprioceptive information from muscle spindles in the low back is influenced by small changes in the previous length history of lumbar muscles.

Plane of vertebral movement eliciting muscle lengthening history in the low back influences the decrease in muscle spindle responsiveness of the cat.

Proprioceptive feedback is thought to play a significant role in controlling both lumbopelvic and intervertebral orientations. In the lumbar spine, a vertebra's positional history along the dorsal-ventral axis has been shown to alter the position, movement, and velocity sensitivity of muscle spindles in the multifidus and longissimus muscles. These effects appear due to muscle history. Because spinal motion segments have up to 6 degrees of freedom for movement, we were interested in whether the axis along which the history is applied differentially affects paraspinal muscle spindles. We tested the null hypothesis that the loading axis, which creates a vertebra's positional history, has no effect on a lumbar muscle spindle's subsequent response to vertebral position or movement. Identical displacements were applied along three orthogonal axes directly at the L(6) spinous process using a feedback motor system under displacement control. Single-unit nerve activity was recorded from 60 muscle spindle afferents in teased filaments from L(6) dorsal rootlets innervating intact longissimus or multifidus muscles of deeply anesthetized cats. Muscle lengthening histories along the caudal-cranial and dorsal-ventral axis, compared with the left-right axis, produced significantly greater reductions in spindle responses to vertebral position and movement. The spinal anatomy suggested that the effect of a lengthening history is greatest when that history had occurred along an axis lying within the anatomical plane of the facet joint. Speculation is made that the interaction between normal spinal mechanics and the inherent thixotropic property of muscle spindles poses a challenge for feedback and feedforward motor control of the lumbar spine.

Time course for the development of muscle history in lumbar paraspinal muscle spindles arising from changes in vertebral position.

BACKGROUND CONTEXT: In neutral spinal postures with low loading moments, the lumbar spine is not inherently stable. Small compromises in paraspinal muscle activity may affect lumbar spinal biomechanics. Proprioceptive feedback from muscle spindles is considered important for control of muscle activity. Because skeletal muscle and muscle spindles are thixotropic, their length history changes their physical properties. The present study explores a mechanism that can affect the responsiveness of paraspinal muscle spindles in the lumbar spine. PURPOSE: This study has the following two aims: to extend our previous findings demonstrating the history-dependent effects of vertebral position on the responsiveness of lumbar paraspinal muscle spindles and to determine the time course for these effects. Based on previous studies, if a cross-bridge mechanism underlies these thixotropic effects, then the relationship between the magnitude of spindle discharge and the duration of the vertebral position will be one of exponential decay or growth. STUDY DESIGN/SETTING: A neurophysiological study using the lumbar spine in a feline model. METHODS: The discharge from individual muscle spindle afferents innervating lumbar paraspinal muscles in response to the duration and direction of vertebral position was obtained from teased filaments in the L(6) dorsal roots of 30 Nembutal-anesthetized cats. The L(6) vertebra was controlled using a displacement-controlled feedback motor and was held in each of three different conditioning positions for durations of 0, 0.5, 1, 1.5, and 2 seconds. Two of the conditioning positions stretched or shortened the lumbar muscles relative to an intermediate conditioning position. Conditioning positions for all cats ranged from 0.9 to 2.0mm dorsal- and ventralward relative to the intermediate position. These magnitudes were determined based on the displacement that loaded the L(6) vertebra to 50% to 60% of the cat's body weight. Conditioning was thought to simulate a motion segment's position that might be passively maintained because of fixation, external load, a prolonged posture, or structural change. After conditioning positions that stretched (hold-long) and shortened (hold-short) the spindle, the vertebra was repositioned identically and muscle spindle discharge at rest and to movement was compared with having conditioned at the intermediate position. RESULTS: Lumbar vertebral positions maintained for less than 2 seconds were capable of evoking different discharge rates from lumbar paraspinal muscle spindles despite the vertebra having been returned to an identical locations. Both resting spindle discharge and their responsiveness to movement were altered. Conditioning vertebral positions that stretched the spindles decreased spindle activity and positions that unloaded the spindles increased spindle activity on returning the vertebra to its identical original (intermediate) position. The magnitude of these effects increased as conditioning duration increased to 2 seconds. These effects developed with a time course following a first-order exponential reaching a maximal value after approximately 4 seconds of history. The time constant for a hold-short history was 2.6 seconds and for a hold-long history was approximately half of that at 1.1 seconds. CONCLUSIONS: Thixotropic contributions to the responsiveness of muscle spindles in the low back are caused by the rapid, spontaneous formation of stable crossbridges. These sensory alterations because of vertebral history would represent a proprioceptive input not necessarily representative of the current state of intersegmental positioning. As such, they would constitute a source of inaccurate sensory feedback. Examples are presented suggesting ways in which this novel finding may affect spinal physiology.

Response of lumbar paraspinal muscles spindles is greater to spinal manipulative loading compared with slower loading under length control.

BACKGROUND CONTEXT: Spinal manipulation (SM) is a form of manual therapy used clinically to treat patients with low back and neck pain. The most common form of this maneuver is characterized as a high-velocity (duration <150 ms), low-amplitude (segmental translation <2 mm, rotation <4 degrees , and applied force 220-889 N) impulse thrust (high-velocity, low-amplitude spinal manipulation [HVLA-SM]). Clinical skill in applying an HVLA-SM lies in the practitioner's ability to control the duration and magnitude of the load (ie, the rate of loading), the direction in which the load is applied, and the contact point at which the load is applied. Control over its mechanical delivery is presumably related to its clinical effects. Biomechanical changes evoked by an HVLA-SM are thought to have physiological consequences caused, at least in part, by changes in sensory signaling from paraspinal tissues. PURPOSE: If activation of afferent pathways does contribute to the effects of an HVLA-SM, it seems reasonable to anticipate that neural discharge might increase or decrease in a nonlinear fashion as the thrust duration approaches a threshold value. We hypothesized that the relationship between the duration of an impulsive thrust to a vertebra and paraspinal muscle spindle discharge would be nonlinear with an inflection near the duration of an HVLA-SM delivered clinically (<150 ms). In addition, we anticipated that muscle spindle discharge would be more sensitive to larger amplitude thrusts. STUDY DESIGN/SETTING: A neurophysiological study of spinal manipulation using the lumbar spine of a feline model. METHODS: Impulse thrusts (duration: 12.5, 25, 50, 100, 200, and 400 ms; amplitude 1 or 2 mm posterior to anterior) were applied to the spinous process of the L6 vertebra of deeply anesthetized cats while recording single unit activity from dorsal root filaments of muscle spindle afferents innervating the lumbar paraspinal muscles. A feedback motor was used in displacement control mode to deliver the impulse thrusts. The motor's drive arm was securely attached to the L6 spinous process via a forceps. RESULTS: As thrust duration became shorter, the discharge of the lumbar paraspinal muscle spindles increased in a curvilinear fashion. A concave-up inflection occurred near the 100-ms duration eliciting both a higher frequency discharge compared with the longer durations and a substantially faster rate of change as thrust duration was shortened. This pattern was evident in paraspinal afferents with receptive fields both close and far from the midline. Paradoxically, spindle afferents were almost twice as sensitive to the 1-mm compared with the 2-mm amplitude thrust (6.2 vs. 3.3 spikes/s/mm/s). This latter finding may be related to the small versus large signal range properties of muscle spindles. CONCLUSIONS: The results indicate that the duration and amplitude of a spinal manipulation elicit a pattern of discharge from paraspinal muscle spindles different from slower mechanical inputs. Clinically, these parameters may be important determinants of an HVLA-SM's therapeutic benefit.

Vertebral position alters paraspinal muscle spindle responsiveness in the feline spine: effect of positioning duration.

Proprioceptive information from paraspinal tissues including muscle contributes to neuromuscular control of the vertebral column. We investigated whether the history of a vertebra's position can affect signalling from paraspinal muscle spindles. Single unit recordings were obtained from muscle spindle afferents in the L6 dorsal roots of 30 Nembutal-anaesthetized cats. Each afferent's receptive field was in the intact muscles of the low back. The L6 vertebra was controlled using a displacement-controlled feedback motor and was held in each of three different conditioning positions for durations of 0, 2, 4, 6 and 8 s. Conditioning positions (1.0-2.2 mm dorsal and ventral relative to an intermediate position) were based upon the displacement that loaded the L6 vertebra to 50-60% of the cat's body weight. Following conditioning positions that stretched (hold-long) and shortened (hold-short) the spindle, the vertebra was repositioned identically and muscle spindle discharge at rest and to movement was compared with conditioning at the intermediate position. Hold-short conditioning augmented mean resting spindle discharge by +4.1 to +6.2 impulses s(-1); however, the duration of hold-short did not significantly affect this increase (F(4,145) = 0.49, P = 0.74). The increase was maintained at the beginning of vertebral movement but quickly returned to baseline. Conversely, hold-long conditioning significantly diminished mean resting spindle discharge by -2.0 to -16.1 impulses s(-1) (F(4,145) = 11.23, P < 0.001). The relationship between conditioning duration and the diminished resting discharge could be described by a quadratic (F(1,145) = 9.28, P = 0.003) revealing that the effects of positioning history were fully developed within 2 s of conditioning. In addition, 2 s or greater of hold-long conditioning significantly diminished spindle discharge to vertebral movement by -5.7 to -10.0 impulses s(-1) (F(4,145) = 11.0, P < 0.001). These effects of vertebral positioning history may be a mechanism whereby spinal biomechanics interacts with the spine's proprioceptive system to produce acute effects on neuromuscular control of the vertebral column.