Dean Kriellaars

On the regulation of repetitive firing in lumbar motoneurones during fictive locomotion in the cat

SummaryRepetitive firing of motoneurones was examined in decerebrate, unanaesthetised, paralysed cats in which fictive locomotion was induced by stimulation of the mesencephalic locomotor region. Repetitive firing produced by sustained intracellular current injection was compared with repetitive firing observed during fictive locomotion in 17 motoneurones. During similar interspike intervals, the afterhyperpolarisations (AHPs) during fictive locomotion were decreased in amplitude compared to the AHPs following action potentials produced by sustained depolarising current injections. Action potentials were evoked in 10 motoneurones by the injection of short duration pulses of depolarising current throughout the step cycles. When compared to the AHPs evoked at rest, the AHPs during fictive locomotion were reduced in amplitude at similar membrane potentials. The post-spike trajectories were also compared in different phases of the step cycle. The AHPs following these spikes were reduced in amplitude particularly in the depolarised phases of the step cycles. The frequency-current (f-I) relations of 7 motoneurones were examined in the presence and absence of fictive locomotion. Primary ranges of firing were observed in all cells in the absence of fictive locomotion. In most cells (6/7), however, there was no relation between the amount of current injected and the frequency of repetitive firing during fictive locomotion. In one cell, there was a large increase in the slope of the f-I relation. It is suggested that this increase in slope resulted from a reduction in the AHP conductance; furthermore, the usual elimination of the relation is consistent with the suggestions that the repetitive firing in motoneurones during fictive locomotion is not produced by somatic depolarisation alone, and that motoneurones do not behave as simple input-output devices during this behaviour. The correlation of firing level with increasing firing frequency which has previously been demonstrated during repetitive firing produced by afferent stimulation or by somatic current injection is not present during fictive locomotion. This lends further support to the suggestion that motoneurone repetitive firing during fictive locomotion is not produced or regulated by somatic depolarisation. It is suggested that although motoneurones possess the intrinsic ability to fire repetitively in response to somatic depolarisation, the nervous system need not rely on this ability in order to produce repetitive firing during motor acts. This capability to modify or bypass specific motoneuronal properties may lend the nervous system a high degree of control over its motor output.

Knee strength deficits after hamstring tendon and patellar tendon anterior cruciate ligament reconstruction.

PURPOSE The purpose of this study was to examine the strength of the knee flexors and knee extensors after two surgical techniques of ACL reconstruction and compare them to an age and activity level matched control group. METHODS Twenty-four subjects who had undergone ACL reconstruction greater than 1 yr previously were placed into one of two groups according to autograft donor site: patellar tendon (BPB; N = 8) and hamstring (H; N = 16), and compared with an active, control group (N = 30). Knee flexor and extensor strength was evaluated using isovelocity dynamometry (5 speeds, eccentric and concentric, 5-95 degrees ROM). Strength maps were used to graphically analyze strength over a broad operational domain of the neuromuscular system. Average strength maps were determined for each autograft group and compared with controls. A difference map (control minus graft group) and confidence (t-test) maps were used to quantitatively identify strength deficits. RESULTS The combined ACL group (N = 24) revealed a global 25.5% extensor strength deficit, with eccentric regional (angle and velocity matched) deficits up to 50% of control. Strength deficits covered over 86% of the sampled strength map area (P < 0.01). These knee extensor strength deficits are greater than previously reported. In addition, the BPB group demonstrated a concentric, low velocity, knee extensor strength deficit at 60-95 degrees that was not observed in the H group. Significant graft site dependent, regional knee flexor deficits of up to 50% of control were observed for the H group. CONCLUSIONS Strength deficits localized to specific contraction types and ranges of motion were demonstrated between the ACL and control groups that were dependent upon autograft donor site. Postoperative rehabilitation protocols specific to these deficits should be devised.

Hamstring and quadriceps strength balance in normal and hamstring anterior cruciate ligament-reconstructed subjects.

Objective:The purpose of this study was to evaluate and characterize the agonist-antagonist strength balance (hamstring/quadriceps [H/Q] ratio and dynamic control ratio [DCR]) about the knee specific to velocity, range of motion, and contraction type. We hypothesized that there would be systematic variation in the H/Q ratio and DCR based on knee joint angle, angular velocity, and contraction type. We also hypothesized that these ratios would be altered in the anterior cruciate ligament (ACL)-reconstructed group in favor of protecting the ACL graft (relative knee flexor strength when strain on the ACL is the greatest). Design:Cross-sectional design. Setting:A tertiary care sport medicine clinic. Patients or Participants:Sixteen subjects more than 1 year after hamstring tendon ACL reconstruction were compared with 30 active uninjured control subjects. Interventions:Isokinetic strength testing was performed over 5° to 95° knee joint range of motion, 5 angular velocities (50, 100, 150, 200, 250°/s), for concentric and eccentric contractions. Main Outcome Measurements:Angle and velocity-matched H/Q ratio maps and DCR maps were produced for each group. Difference maps allowed quantification of the differences between the groups. Results:Angle and velocity-matched H/Q ratio maps demonstrated systematic variation based on joint angle, velocity, and contraction type for both the control (H/Q, ~0–1.42; DCR, ~0–1.57) and the ACL-reconstructed group (H/Q, ~0–1.33; DCR, ~0–1.35). Difference maps demonstrate regional (angle and velocity-specific) alteration in the ratio between the ACL-reconstructed and control groups. Conclusions:Specific imbalances were demonstrated in the ACL-reconstructed group compared with control. In high knee flexion angles, the low H/Q ratio may represent a compromised ability of the hamstrings to stabilize the knee joint throughout the full range of motion. Near full knee extension shifts in favor of the knee flexors may represent an attempt to stabilize the knee at the angle of greatest ACL strain. These finding have implications for graft donor site selection and postoperative rehabilitation as well as provide insight into the neuromuscular control of the knee.

Hip strength following hamstring tendon anterior cruciate ligament reconstruction.

Objective:The objective of this study was to determine whether there is alteration in resultant joint moment of the hip extensors and adductors after hamstring anterior cruciate ligament (ACL) reconstruction. Design:Cross-sectional outcome analysis. Setting:University sport medicine center. Subjects:Fifteen subjects more than 1 year after ACL reconstruction with semitendinosus and gracilis tendons were compared with 15 matched controls with no knee injury. Interventions:Strength testing of the hip extensors and hip adductors of both limbs. Main Outcome Measurements:Isokinetic (50°/s and 150°/s) hip extensor strength test and isometric (15° and 30°) hip adductor strength test. Results:Hip extensors increase in strength after hamstring ACL reconstruction, evening out normal side-to-side strength differences. Hip adductor strength deficits of up to 43% are demonstrated in the ACL reconstructed subjects compared with controls. Conclusions:The identification of hip adductor strength deficits after hamstring harvest for ACL reconstruction may have important implications for both graft harvest site selection as well as postoperative rehabilitation protocols. Given the known existence of knee strength deficits after ACL reconstruction, increases in isovelocity hip extensor strength may contribute to increased lower limb strength imbalances. This may have implications for the ability of the lower limb muscles to protect the ACL graft.

The effect of pedometer position and normal gait asymmetry on step count accuracy

Manufacturers of pedometers recommend wearing a pedometer on the midline of the right thigh and this recommendation is used in research. However, there is conflicting evidence regarding the effect of pedometer position on accuracy. The purpose of this study was to systematically evaluate the effect of pedometer position on accuracy for 3 modes of gait. The Yamax SW200 pedometer was evaluated in 20 subjects in 5 different positions simultaneously: left mid-axillary, left mid-thigh, umbilical, right mid-thigh, and right mid-axillary. Each subject was asked to walk on a treadmill (54, 80, and 107 m.min(-1)), to walk overground (slow, preferred, and fast speeds), and to ascend and descend stairs. Pedometer steps were recorded and compared with actual steps observed. Using the same protocol, instantaneous triaxial accelerometry was used to explain position-dependent differences in accuracy. At slow speeds, the left mid-axillary position demonstrated the lowest net mean (+/-SD) error across all modes of gait (7.7% (+/-11.6%) overground;-0.6% (+/-2.2%) stairs). The right mid-thigh position had significantly (p<0.01) higher error for treadmill (18.1% (+/-17.3%)), overground (12.9% (+/-15.2%)), and stairs (2.9% (+/-3.9%)). Pedometer position dependent error was demonstrated, with the left mid-axillary position superior to the recommended position of right mid-thigh. The greater accuracy on the left side was wholly explained by gait asymmetry evident in step-induced accelerations recorded at right and left pedometer positions. A model of absolute error based on the ratio of steps at different gait speeds was generated to demonstrate the importance of this finding in pedometer-based lifestyle intervention studies.

Effects of intradialytic cycling compared with pedometry on physical function in chronic outpatient hemodialysis: a prospective randomized trial

BACKGROUND Individuals on hemodialysis have low physical function and activity levels. Clinical trials have shown improvements in these parameters with exercise programming. Pedometers have not been extensively evaluated in individuals on hemodialysis. This randomized clinical trial compared the effects of intradialytic cycling versus a pedometer program on physical function, physical activity and quality of life. METHODS Sixty patients were randomly assigned to two study groups. The ergometer group cycled during each hemodialysis session for 24 weeks. Pedometer participants followed a home-based walking program for 24 weeks. The primary outcome was aerobic capacity [VO2peak and 6-minute walk (6MW) test]. Secondary outcomes included lower extremity strength [sit-to-stand (SS) test], flexibility [sit-and-reach (SR) test], physical activity (accelerometer) and health-related quality of life. Measurements were collected at baseline and at 12 and 24 weeks. RESULTS At 12 and 24 weeks, there was no significant change in the VO2peak or 6MW test between or within study groups. SS testing in the ergometer group improved from 10.2 (SD 3.4) to 11.4 (SD 2.5) cycles from baseline to 24 weeks (P < 0.005). Similarly, in the pedometer group, SS cycles improved from 10.1 (SD 3.3) to 12.2 (SD 3.5) (P < 0.005). The SR test also significantly improved over time in both the study groups. No significant changes were noted for other secondary outcomes. CONCLUSIONS Both intradialytic cycling and pedometer programming improved aspects of physical function. Neither intervention had a significant effect on aerobic capacity. No significant differences in any outcomes were identified between interventions groups.

Relationship between ambulatory performance and self-rated disability in patients with lumbar spinal stenosis.

Study Design. A cross-sectional study. Objective. To identify the relationship between performance measures derived from accelerometry and subjective reports of pain, disability, and health in patients with lumbar spinal stenosis (LSS). Summary of Background Data. Accelerometers have emerged as a measure of performance, providing the ability to characterize the pattern and magnitude of real-life activity, and sedentarism. Pain and loss of function, particularly ambulation, are common in LSS. The extent to which pain, perceived disability, and self-rated health relate to performance in patients with LSS is not well known. Methods. Data regarding self-reported pain, disability (Oswestry Disability Index, Roland-Morris Disability Questionnaire, and Disabilities of the Arm, Shoulder, and Hand), and health (36-Item Short Form Health Survey [SF-36]) were collected from patients with LSS (n = 33). Physical activity, ambulation, and inactivity performance measures were derived from 7-day accelerometer records. Correlation and stepwise regression were used. Results. The physical function subscale of the SF-36, a non–pathology-specific outcome, had the best overall correlation to physical activity and ambulation (average r = 0.53) compared with pain (average r = 0.32) and disability (average r = −0.45) outcomes. Stepwise regression models for performance were predominantly single-variable models (4 of 8 models); pain was not selected as a predictor. A second non–pathology-specific outcome, the Disabilities of Arm Shoulder and Hand, improved the prediction of performance in 5 of 8 models. Conclusion. Subjective measures of pain and disability had limited ability to account for real-life performance in patients with LSS. Future research is required to identify determinants of performance in patients with LSS because barriers to activity may not be disease-specific.

Relationship Between Sleep, Pain, and Disability in Patients With Spinal Pathology

OBJECTIVE To characterize sleep and its relationship with disability and pain in patients with spine pathology. DESIGN A survey study. SETTING A university-based hospital spine clinic. PARTICIPANTS Subjects (N=121) with mixed-etiology spine pathology. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Self-reported disability (Oswestry Disability Index [ODI]), back and leg pain intensity, the effect of back or leg pain on function, and sleep (Pittsburgh Sleep Quality Index [PSQI]) assessments were completed. RESULTS Severe disability was evident with a mean ODI ± SD of 54.9±14, with mean pain intensities ± SD of 50±30 mm and 54±27 mm of 100mm for the leg and back, respectively. The mean PSQI ± SD was 10.4±5.3, with 87% of participants scoring greater than the sleep-disordered threshold of 5. PSQI was correlated to ODI (r=.53, P<.001), and ODI without the sleep component (r=.47, P<.001). Six of the subscales of PSQI were all also significantly correlated to ODI (.25<r<.42, P<.05). Stepwise regression (ODI dependent variables; PSQI, pain intensity and function, age, body mass index as independent variables) was performed. PSQI was retained in the model along with 2 pain measures (r(2)=.50, P<.001). Substitution of the 7 subscales for the overall PSQI score revealed 2 subscales (sleep quality, use of sleep medications) as predictors of ODI (r(2)=.490, P<.001). CONCLUSIONS Despite its being intuitive that sleep disorders will be present in patients with spinal disorders, it was surprising that sleep quality was an independent predictor of disability along with pain. Furthermore, sleep quality is more closely correlated to disability than leg pain, which is the current focus of medical interventions.

Critical Considerations for Physical Literacy Policy in Public Health, Recreation, Sport, and Education Agencies

ABSTRACT The International Charter for Physical Education, Physical Activity, and Sport clearly states that vested agencies must participate in creating a strategic vision and identify policy options and priorities that enable the fundamental right for all people to participate in meaningful physical activity across their life course. Physical literacy is a rapidly evolving concept being used in policy making, but it has been limited by pre-existing and sometimes biased interpretations of the construct. The aim of this article is to present a new model of physical literacy policy considerations for key decision makers in the fields of public health, recreation, sport, and education. Internationally debated definitions of physical literacy and the wider construct of literacy were reviewed in order to establish common pillars of physical literacy in an applicable policy model. This model strives to be consistent with international understandings of what “physical literacy” is, and how it can be used to achieve established and developing public health, recreation, sport, and educative goals.

Body segment inertial parameters and low back load in individuals with central adiposity

There is a paucity of information regarding the impact of central adiposity on the inertial characteristics of body segments. Deriving low back loads during lifting requires accurate estimate of inertial parameters. The purpose was to determine the body segment inertial parameters of people with central adiposity using a photogrammetric technique, and then to evaluate the impact on lumbar spine loading. Five participants with central adiposity (waist:hip ratio>0.9, waist circumference>102 cm) were compared to a normal BMI group. A 3D wireframe model of the surface topography was constructed, partitioned into 8 body segments and then body segment inertial parameters were calculated using volumetric integration assuming uniform segment densities for the segments. Central adiposity dependent increases in body segment parameters ranged from 12 to 400%, varying across segments (greatest for trunk) and parameters. The increase in mass distribution to the trunk was accompanied by an anterior and inferior shift of the centre of mass. A proximal shift in centre of mass was detected for the extremities, along with a reduction in mass distribution to the lower extremity. L5/S1 torques (392 vs 263 Nm) and compressive forces (5918 vs 3986 N) were substantially elevated in comparison to the normal BMI group, as well as in comparison to torques and forces predicted using published BSIP equations. Central adiposity resulted in substantial but non-uniform increases in inertial parameters resulting in task specific increases in torque and compressive loads arising from different inertial and physical components.