Simple change in initial standing position enhances the initiation of gait

PURPOSE

Older adults and individuals with Parkinson's disease exhibit impaired gait initiation performance with less effective anticipatory postural adjustments (APA) and less dynamic stepping characteristics. These observations may reflect impaired interactions between the postural and locomotor components of this task. The purpose of this study was to evaluate the effectiveness of altering the stance position of the initial swing limb on improving APA characteristics and stepping performance.

METHODS

Three groups (healthy young adults, individuals with Parkinson's disease, and age-matched older adults) of 12 participants initiated gait from three initial stance conditions: normal, backward displaced swing limb, and forward displaced swing limb. Ground reaction forces and whole body kinematics were recorded to characterize the APA and step parameters.

RESULTS

Initiating gait from the back condition produced more forceful weight shifting (P < 0.001), greater propulsive forces (P < 0.001), and faster center-of-mass velocities throughout the stepping phases (P < 0.05).

CONCLUSIONS

Translating the swing limb 0.5-ft-length backward seems to enhance the interaction between posture and locomotion, which may have therapeutic potential for improving gait initiation performance.

Pain-related fear and catastrophizing predict pain intensity and disability independently using an induced muscle injury model

Timing of assessment of psychological construct is controversial and results differ based on the model of pain induction. Previous studies have not used an exercise-induced injury model to investigate timing of psychological assessment. Exercise-induced injury models may be appropriate for these investigations because they approximate clinical pain conditions better than other experimental stimuli. In this study we examined the changes of psychological constructs over time and determined whether timing of assessment affected the construct's association with reports of pain intensity and disability. One-hundred twenty-six healthy volunteers completed the Fear of Pain Questionnaire (FPQ-III), Pain Catastrophizing Scale (PCS), and Tampa Scale of Kinesiophobia (TSK) prior to inducing muscle injury to the shoulder. The PCS and TSK were measured again 48 and 96 hours postinjury induction. Pain intensity and disability were collected at 48 and 96 hours and served as dependent variables in separate regression models. Results indicated that the FPQ-III had the strongest prediction of pain intensity from baseline to 96 hours. After baseline the PCS and TSK were stronger predictors of pain intensity and disability, respectively. These data provide support for the use of psychological constructs in predicting outcomes from shoulder pain. However, they deviate from the current theoretical model indicating that fear of pain is a consequence of injury and instead suggests that fear of pain before injury may influence reports of pain intensity.

PERSPECTIVE

The current study provides evidence that fear of pain can be assessed prior to injury. Furthermore, it supports that after injury pain catastrophizing and kinesiophobia are independently associated with pain and disability. Overall these data suggest that timing of psychological assessment may be an important consideration in clinical environments.

The influence of sex, age and BMI on the degeneration of the lumbar spine

Previous research on lumbar spine osteophyte formation has focused on patterned development and the relation of age and sex to degeneration within the vertebral bodies. The inclusion of osteophytes originating on the laminae and body mass index (BMI) may result in a more complete evaluation. This study investigates lumbar osteophyte development on the laminae and vertebral bodies to determine whether osteophyte development: (i) is related bilaterally, at different lumbar levels, and superior and inferior margins; (ii) on the laminae and vertebral bodies are reciprocally dependent responses; (iii) is correlated with sex, age and/or BMI. Seventy-six individuals (39 females, 37 males) were randomly selected from a modern skeletal collection (Bass Donated Collection). Osteophyte development was scored in eight regions on each vertebra at all five lumbar levels. A factor analysis considered all 40 scoring regions and Pearson's correlation analyses assessed the relatedness of age and BMI with the consequent factors. The factor analysis separated the variables into two similar factors for males and females defined as: (i) superior and inferior vertebral body scores and (ii) superior laminar scores at higher lumbar levels. The factor analysis also determined a third factor for females defined as: (iii) inferior laminar scores at lower lumbar levels. The severity of vertebral body osteophytes increased with age for both sexes. Additionally for females, as BMI increased, osteophyte severity increased for both the superior laminar margins higher in the column and the vertebral bodies. Dissimilarities between the factors in males and females and the correlation of BMI to osteophyte severity exclusively in females provide evidence for different biomechanical processes influencing osteophyte development.

Decreased static and dynamic postural control in children with autism spectrum disorders

The purpose of this study was to investigate postural control in children with Autism Spectrum Disorders (ASD) during static and dynamic postural challenges. We evaluated postural sway during quiet stance and the center of pressure (COP) shift mechanism during gait initiation for 13 children with ASD and 12 age-matched typically developing (TD) children. Children with ASD produced 438% greater normalized mediolateral sway (p<0.05) and 104% greater normalized anteroposterior sway (p<0.05) than TD children. Consequently, normalized sway area was also significantly greater (p<0.05) in the group with ASD. Similarly, the maximum separation between the COP and center of mass (COM) during quiet stance was 100% greater in the anteroposterior direction (p<0.05) and 146% greater in the resultant direction (p<0.05) for children with ASD. No significant difference was observed in the mediolateral direction, in spite of the 123% greater separation detected in children with ASD. During gait initiation, no group differences were detected in the posterior COP shift mechanism, suggesting the mechanism for generating forward momentum is intact. However, significantly smaller lateral COP shifts (p<0.05) were observed in children with ASD, suggesting instability or an alternative strategy for generating momentum in the mediolateral direction. These results help to clarify some discrepancies in the literature, suggesting an impaired or immature control of posture, even under the most basic conditions when no afferent or sensory information have been removed or modified. Additionally, these findings provide new insight into dynamic balance in children with ASD.

Lower trunk kinematics and muscle activity during different types of tennis serves

BACKGROUND

To better understand the underlying mechanisms involved in trunk motion during a tennis serve, this study aimed to examine the (1) relative motion of the middle and lower trunk and (2) lower trunk muscle activity during three different types of tennis serves - flat, topspin, and slice.

METHODS

Tennis serves performed by 11 advanced (AV) and 8 advanced intermediate (AI) male tennis players were videorecorded with markers placed on the back of the subject used to estimate the anatomical joint (AJ) angles between the middle and lower trunk for four trunk motions (extension, left lateral flexion, and left and right twisting). Surface electromyographic (EMG) techniques were used to monitor the left and right rectus abdominis (LRA and RRA), external oblique (LEO and REO), internal oblique (LIO and RIO), and erector spinae (LES and RES). The maximal AJ angles for different trunk motions during a serve and the average EMG levels for different muscles during different phases (ascending and descending windup, acceleration, and follow-through) of a tennis serve were evaluated.

RESULTS

The repeated measures Skill x Serve Type x Trunk Motion ANOVA for maximal AJ angle indicated no significant main effects for serve type or skill level. However, the AV group had significantly smaller extension (p = 0.018) and greater left lateral flexion (p = 0.038) angles than the AI group. The repeated measures Skill x Serve Type x Phase MANOVA revealed significant phase main effects in all muscles (p < 0.001) and the average EMG of the AV group for LRA was significantly higher than that of the AI group (p = 0.008). All muscles showed their highest EMG values during the acceleration phase. LRA and LEO muscles also exhibited high activations during the descending windup phase, and RES muscle was very active during the follow-through phase.

CONCLUSION

Subjects in the AI group may be more susceptible to back injury than the AV group because of the significantly greater trunk hyperextension, and relatively large lumbar spinal loads are expected during the acceleration phase because of the hyperextension posture and profound front-back and bilateral co-activations in lower trunk muscles.

Jump-landing direction influences dynamic postural stability scores

The purpose of this investigation was to determine dynamic postural stability differences among forward, diagonal, and lateral single leg-hop-stabilization protocols in healthy subjects. A one-within repeated measures design was used to determine the effects of jump direction on dynamic postural stability during landing. Subjects were required to perform a two-legged forward, diagonal, and lateral jump to a height equivalent to 50% of their maximum vertical leap, land on a single leg and balance for three seconds. Twenty-six subjects [10 males (22+/-3.9 years of age, 70.9+/-7.6kg, and 176.8+/-6.5cm) and 16 females (20.6+/-.5 years of age, 65.6+/-9.1kg, and 166.4+/-5.9cm)] volunteered to participate in this investigation. Dynamic postural stability indices for the anterior/posterior, medial/lateral, and vertical planes were collected during jump-landing trials of each direction. The results of the investigation show that medial/lateral and vertical dynamic postural stability were significantly affected by the direction of the jump. More specifically, lateral and diagonal jump-landings produce increased medial/lateral stability index (MLSI) scores and forward jump-landings produce increased vertical stability index (VSI) scores. The results suggest that in a healthy population, jump protocol direction will statistically affect dynamic postural stability in the frontal and vertical planes. These alterations could be exacerbated in individuals with lower extremity impairments and further research is warranted.

Pre- and post-impact muscle activation in the tennis volley: effects of ball speed, ball size and side of the body

AIM

To examine the pre- and post-impact activation of five upper extremity muscles in the tennis volley across conditions of ball speed, ball type and side of the body.

METHODS

A repeated measures design in a biomechanics laboratory setting was used. A total of 24 recreational tennis players (mean (SD) age 24 (5) years, height 176 (10) cm, mass 76 (13) kg) were recruited from a university. Participants performed tennis volleys under 18 ball conditions: three ball speeds (slow, medium and fast), with three ball types (two oversize and one regular size) each from two sides (forehand and backhand). Average normalised electromyographic levels of the flexor carpi radialis, extensor carpi radialis, triceps brachii, anterior/middle deltoid and posterior/middle deltoid of the hitting arm during pre- and post-impact phases (200 ms before and after ball-racquet impact, respectively) were assessed.

RESULTS

For the pre-impact phase, a significant muscle and side interaction (p<0.001) and significant main effects for speed (p = 0.002) and muscle (p<0.001) were observed. For the post-impact phase, significant interactions were observed for ball type and side (p = 0.002), ball speed and side (p = 0.011) and muscle and side (p = 0.001), as well significant main effects for muscle (p<0.001), speed (p = 0.035) and side (p<0.001).

CONCLUSION

Oversize tennis balls do not significantly increase upper extremity muscle activation compared to regular size balls during a tennis volley. The highest post-impact activation was observed in the ECR indicating a vigorous wrist stabilisation role that could irritate players with lateral epicondylalgia.

Failed jump landing trials: deficits in neuromuscular control

The purpose of this investigation was to compare neuromuscular control variables during successful and failed jump landings in multiple directions (sagittal, diagonal, and lateral). All data were collected during a single leg hop stabilization maneuver, which required subjects to stand 70 cm from the center of a force plate, jump off both legs, touch a designated marker placed at a height equivalent to 50% of their maximum vertical jump, and land on a single leg for all directions. Twenty-six subjects [10 males (22+/-3.9 years of age, 70.9+/-7.6 kg, and 176.8+/-0.5 cm) and 16 females (20.6+/-0.5 years of age, 65.6+/-9.1 kg, and 166.4+/-5.9 cm)] volunteered to participate in this investigation. Muscle activation times, average preparatory, and reactive electromyographic (EMG) amplitudes were calculated for the vastus medialis, semi-membranosis, lateral gastrocnemius, and tibialis anterior. EMG data revealed that successful jump landing trials had earlier activation times and higher preparatory and reactive EMG amplitudes. There was no difference for EMG activation times or amplitudes among directions. The results indicate neuromuscular control differences between successful and failed trials because of earlier muscle onset and greater amplitude. The results also suggest that in a healthy population, the direction of the jump protocol will not affect lower extremity EMG characteristics.

Dynamic Postural Stability Deficits in Subjects with Self-Reported Ankle Instability

PURPOSE

A limited understanding of how functional ankle instability (FAI) affects dynamic postural stability exists because of a lack of reliable and valid measures. Therefore, the purpose of this investigation was to determine whether a new reliable index for dynamic postural stability could differentiate between those with stable ankles and those with FAI.

METHODS

Data were collected on 108 subjects (54 subjects with stable ankles (STABLE group); 54 subjects with functionally unstable ankles (FAI group)). Subjects performed a single-leg-hop stabilization maneuver in which they stood 70 cm from the center of a force plate, jumped off both legs, touched a designated marker placed at a height equivalent to 50% of their maximum vertical leap, and landed on a single leg. The dynamic postural stability index and directional stability indices (medial/lateral, anterior/posterior, and vertical) were calculated. The raw and normalized (to energy dissipated) indices were compared between groups.

RESULTS

Significant differences were noted for the anterior/posterior stability index (FAI = 0.36 +/- 0.09, STABLE = 0.30 +/- 0.06). Similar results were seen for the vertical stability index (FAI = 0.73 +/- 0.17, STABLE = 0.61 +/- 0.13), the normalized dynamic postural stability index (FAI = 0.85 +/- 0.17, STABLE = 0.73 +/- 0.12), the normalized vertical stability index (FAI = 0.007 +/- 0.004, STABLE = 0.005 +/- 0.001), and the dynamic postural stability index (FAI = 0.008 +/- 0.003, STABLE = 0.006 +/- 0.001).

CONCLUSIONS

These results indicate that the dynamic postural stability index is a sensitive measure of dynamic postural stability and is capable of detecting differences between individuals with stable ankles and individuals with functionally unstable ankles.