Justin J. Kavanagh

Accelerometry: A technique for quantifying movement patterns during walking

The popularity of using accelerometer-based systems to quantify human movement patterns has increased in recent years for clinicians and researchers alike. The benefits of using accelerometers compared to more traditional gait analysis instruments include low cost; testing is not restricted to a laboratory environment; accelerometers are small, therefore walking is relatively unrestricted; and direct measurement of 3D accelerations eliminate errors associated with differentiating displacement and velocity data. However, accelerometry is not without its disadvantages, an issue which is scarcely reported in gait analysis literature. This paper reviews the use of accelerometer technology to investigate gait-related movement patterns, and addresses issues of acceleration measurement important for experimental design. An overview of accelerometer mechanics is provided before illustrating specific experimental conditions necessary to ensure the accuracy of gait-related acceleration measurement. A literature review is presented on how accelerometry has been used to examine basic temporospatial gait parameters, shock attenuation, and segmental accelerations of the body during walking. The output of accelerometers attached to the upper body has provided useful insights into the motor control of normal walking, age-related differences in dynamic postural control, and gait patterns in people with movement disorders.

Age-related differences in postural reaction time and coordination during voluntary sway movements

The elderly are known to exhibit declines in postural control during standing and walking, however little is known about how the elderly react under time-critical and challenging postural situations. The purpose of this study was to examine age-related differences in reaction time (RT) and the pattern of temporal coordination between center of pressure (COP), trunk and head motion during voluntary postural sway movements. Healthy young (n=10; mean=24 years; SD=5 years) and elderly men (n=8; mean=75 years; SD=2 years) stood on a force plate with tri-axial accelerometers attached to the head and lower trunk. Participants were required to generate sway in the anterior-posterior (AP) or medial-lateral (ML) direction in response to an auditory cue during two different testing conditions called Static reaction and Dynamic reaction. Static reactions involved the initiation of voluntary sway in either the AP or ML direction from quiet stance. Dynamic reactions involved an orthogonal switch of voluntary sway between the AP and ML directions. Compared to the young, elderly individuals exhibited slower RT during both Static and Dynamic reaction, and smaller differences in RT and phasing between COP, trunk, and head motion. The results of this study suggest that the elderly adopted more rigid coordination strategies compared to the young when executing a rapid change in direction of whole body motion. The rigid movement strategy of the elderly was presumably generated in an effort to compensate for increased challenge to the maintenance of stability.

Lower trunk motion and speed-dependence during walking

BackgroundThere is a limited understanding about how gait speed influences the control of upper body motion during walking. Therefore, the primary purpose of this study was to examine how gait speed influences healthy individuals lower trunk motion during overground walking. The secondary purpose was to assess if Principal Component Analysis (PCA) can be used to gain further insight into postural responses that occur at different walking speeds.MethodsThirteen healthy subjects (23 ± 3 years) performed 5 straight-line walking trials at self selected slow, preferred, and fast walking speeds. Accelerations of the lower trunk were measured in the anterior-posterior (AP), vertical (VT), and mediolateral (ML) directions using a triaxial accelerometer. Stride-to-stride acceleration amplitude, regularity and repeatability were examined with RMS acceleration, Approximate Entropy and Coefficient of Multiple determination respectively. Coupling between acceleration directions were calculated using Cross Approximate Entropy. PCA was used to reveal the dimensionality of trunk accelerations during walking at slow and preferred speeds, and preferred and fast speeds.ResultsRMS acceleration amplitude increased with gait speed in all directions. ML and VT trunk accelerations had less signal regularity and repeatability during the slow compared to preferred speed. However, stride-to-stride acceleration regularity and repeatability did not differ between the preferred and fast walking speed conditions, partly due to an increase in coupling between frontal plane accelerations. The percentage of variance accounted for by each trunk acceleration Principal Component (PC) did not differ between grouped slow and preferred, and preferred and fast walking speed acceleration data.ConclusionThe main finding of this study was that walking at speeds slower than preferred primarily alters lower trunk accelerations in the frontal plane. Despite greater amplitudes of trunk acceleration at fast speeds, the lack of regularity and repeatability differences between preferred and fast speeds suggest that features of trunk motion are preserved between the same conditions. While PCA indicated that features of trunk motion are preserved between slow and preferred, and preferred and fast speeds, the discriminatory ability of PCA to detect speed-dependent differences in walking patterns is limited compared to measures of signal regularity, repeatability, and coupling.

Thorax and pelvis kinematics during the downswing of male and female skilled golfers

Thorax and pelvis motion during the golf swing have most frequently been described for male golfers at discrete points during the swing, such as top of backswing (TBS) and ball contact (BC). Less is known about the continual motion and coordination of the thorax and pelvis throughout the downswing for either male or female golfers. The purpose of this study was to present detailed 3D kinematic profiles of thorax and pelvis motion during the downswing, and to determine if differences in kinematics exist between male and female skilled golfers. Thorax and pelvis data were collected from 19 male (26+/-7 years) and 19 female (25+/-7 years) skilled golfers (handicap < or =4) using an optical motion analysis system. 3D segment position, orientation and angular velocity were calculated, along with phase plane trajectories and thorax-pelvis separation angles. At BC males had greater pelvis posterior tilt, greater pelvis and thorax lateral tilt to the right, and less pelvis and thorax axial rotation to the left compared to females. Males achieved greater peak thorax and pelvis angular velocity, and angular velocity at BC, in the anterior-posterior and lateral tilt directions. Phase plane trajectories revealed that males and females had similar thorax lateral tilt and anterior-posterior tilt angular velocity-displacement relationships at TBS, yet by BC males had greater tilt angles and velocities compared to females. Collectively, the results suggest that male and female skilled golfers have different kinematics for thorax and pelvis motion, predominantly for lateral and anterior-posterior tilt. What might be considered optimal swing characteristics for male golfers should not be generalized to female golfers.

Movement Variability in the Golf Swing of Male and Female Skilled Golfers

BACKGROUND Despite the complexity of movement, the swings of skilled golfers are considered to be highly consistent. Interestingly, no direct investigation of movement variability or coupling variability during the swings of skilled golfers has occurred. PURPOSE To determine whether differences in movement variability exist between male and female skilled golfers during the downswing of the full golf swing. METHODS Three-dimensional thorax, pelvis, hand, and clubhead data were collected from 19 male (mean ± SD: age = 26 ± 7 yr) and 19 female (age = 25 ± 7 yr) skilled golfers. Variability of segmental movement and clubhead trajectory were examined at three phases of the downswing using discrete (SD) and continuous analyses (spanning set), whereas variability of intersegment coupling was examined using average coefficient of correspondence. RESULTS Compared with males, females exhibited higher thorax and pelvis variability for axial rotation at the midpoint of the downswing and ball contact (BC). Similarly, thorax-pelvis coupling variability was higher for females than males at both the midpoint of the downswing and BC. Regardless of thorax and pelvis motion, the variability of hand and clubhead trajectory sequentially decreased from the top of the backswing to BC for both males and females. CONCLUSIONS Male and female skilled golfers use different upper body movement strategies during the downswing while achieving similarly low levels of clubhead trajectory variability at BC. It is apparent that the priority of skilled golfers is to progressively minimize hand and clubhead trajectory variability toward BC, despite the individual motion or coupling of the thorax and pelvis.

What Are the Relations Between Voluntary Postural Sway Measures and Falls-History Status in Community-Dwelling Older Adults?

OBJECTIVES To determine whether a series of voluntary postural sway tasks could differentiate and accurately identify the falls-history status of older adults, and to examine the relations between voluntary sway measures and falls risk. DESIGN Case-control study. SETTING University biomechanics laboratory. PARTICIPANTS Healthy community-dwelling older adults (N=51) aged 65 to 94 years who were divided into nonfaller (n=36), single faller (n=10), and multiple faller (n=5) groups based on a 12-month history of falls. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Participants underwent a falls-risk assessment using the Physiological Profile Assessment (PPA) and then performed 6 voluntary postural sway tasks. The tasks included maximum static leans, maximum voluntary sway, continuous voluntary sway, rapid initiation of voluntary sway, rapid termination of voluntary sway, and rapid orthogonal switches of voluntary sway between the anterior-posterior and medial-lateral directions. Center of pressure amplitudes and reaction time measures were examined using analysis of covariance, Pearsons correlation, and discriminant function analyses. RESULTS Multiple fallers had increased age; increased falls risk; slower initiation, termination, and orthogonal switch reaction times; and reduced center of pressure amplitude during sway initiation and continuous voluntary sway compared with nonfallers. Few differences were observed between the nonfallers and single fallers. Voluntary sway measures were significantly correlated with each other and with PPA score. Two postural reaction time measures and age identified 80% of multiple fallers and 98% of nonmultiple fallers. Similarly, PPA score and age identified 80% of multiple fallers and 100% of nonmultiple fallers. CONCLUSIONS The slower and less effective balance responses of multiple fallers compared with nonfallers and the comparable sensitivity and specificity of PPA score and reactive voluntary sway measures indicate that postural reaction time is a strong determinant of falls risk.

Voluntary sway and rapid orthogonal transitions of voluntary sway in young adults, and low and high fall-risk older adults

BACKGROUND Falls amongst older people have been linked to reduced postural stability and slowed movement responses. The objective of this study was to examine differences in postural stability and the speed of response between young adults, low fall-risk older adults, and high fall-risk older adults during voluntary postural sway movements. METHODS Twenty-five young adults (25+/-4 years), and 32 low fall-risk (74+/-5 years), and 16 high fall-risk (79+/-7 years) older adults performed voluntary sway and rapid orthogonal transitions of voluntary sway between the anterior-posterior and medial-lateral directions. Measures included reaction and movement time and the amplitudes of the centre of pressure, centre of mass, and the separation distance between the centre of pressure and centre of mass. FINDINGS Both fall-risk groups compared to the young had slower reaction and movement time, greater centre of pressure and/or centre of mass amplitude in the orthogonal (non-target) direction during voluntary sway, and reduced anterior-posterior and medial-lateral separation between the centre of pressure and centre of mass during voluntary sway and orthogonal transitions. High compared to low fall-risk individuals had slower reaction and movement time, increased non-target centre of mass amplitude during voluntary sway, and reduced medial-lateral centre of pressure and centre of mass separation during voluntary sway and orthogonal transitions. INTERPRETATION Age-related deterioration of postural control resulted in slower reactive responses and reduced control of the direction of body movement during voluntary sway and orthogonal transitions. Slower postural reaction and movement time and reduced medial-lateral control of the centre of mass during voluntary sway movements are associated with increased fall-risk in community-living older people.

The control of upper body segment speed and velocity during the golf swing

Understanding the dynamics of upper body motion during the downswing is an important step in determining the control strategies required for a successful and repeatable golf swing. The purpose of this study was to examine the relationship between head, thorax, and pelvis motion, during the downswing of professional golfers. Three-dimensional data were collected for 14 male professional golfers (age 27 ± 8 years, golf-playing experience 13.3 ± 8 years) using an optical motion analysis system. The amplitude and timing of peak speed and peak velocities were calculated for the head, thorax, and pelvis during the downswing. Cross-correlation analysis was used to examine the strength of coupling and phasing between and within segments. The results indicated the thorax segment had the highest peak speeds and peak velocities for the upper body during the downswing. A strong coupling relationship was evident between the thorax and pelvis (average R 2 = 0.92 across all directions), while the head and thorax showed a much more variable relationship (average R 2 = 0.76 across all directions). The strong coupling between the thorax and pelvis is possibly a method for simplifying the motor control strategy used during the downswing, and a way of ensuring consistent motor patterns.

Influence of exercise intensity and duration on functional and biochemical perturbations in the human heart.

Strenuous endurance exercise induces transient functional and biochemical cardiac perturbations that persist for 24–48 h. The magnitude and time‐course of exercise‐induced reductions in ventricular function and increases in cardiac injury markers are influenced by the intensity and duration of exercise. In a human experimental model, exercise‐induced reductions in ventricular strain and increases in cardiac troponin are greater, and persist for longer, when exercise is performed within the heavy‐ compared to moderate‐intensity exercise domain, despite matching for total mechanical work. The results of the present study help us better understand the dose–response relationship between endurance exercise and acute cardiac stress/injury, a finding that has implications for the prescription of day‐to‐day endurance exercise regimes.

Low dosage promethazine and loratadine negatively affect neuromotor function

OBJECTIVES Determine how the sedating antihistamine promethazine and non-sedating antihistamine loratadine at a dose of 10mg influence voluntary and involuntary motor processes in the hours following ingestion and the morning after ingestion. METHODS Eight healthy young adults were recruited into a human double-blind, placebo-controlled, three-way crossover study. Neuromotor function was examined using a battery of controlled reaction time, postural tremor, and heart rate variability measures. Neuromotor function was assessed 4 times for each of the promethazine, loratadine and placebo interventions; pre-ingestion, 1h post-ingestion, 2h post-ingestion, and the following day. RESULTS Self-perceived levels of drowsiness increased only after ingestion of promethazine. However, both antihistamines had negative effects on simple reaction time, choice reaction time, the RMS and peak power amplitude of postural tremor, and autonomic cardiac regulation. CONCLUSIONS The presence of selective neuromotor deficits following ingestion of promethazine and loratadine suggest that sedating and non-sedating antihistamines alter neuromotor function. It is possible that the H(1) antagonists used in this study have antimuscarinic effects, which may impact on the central dopaminergic system that plays a role in modulating several CNS processes associated with movement. SIGNIFICANCE Antihistamines are one of the most commonly procured over-the-counter medications. The current study suggests that taking non-sedating antihistamines to avoid the adverse drug reaction of drowsiness may not avoid unwanted motor control side-effects.