Jacqueline Alderson

Lower-limb coordination and shoulder joint mechanics in the tennis serve

PURPOSE To examine the relationship between variable lower-limb coordination and shoulder joint kinetics and kinematics in the high-performance flat first serve in tennis. METHODS Three-dimensional data describing three flat serve (FS) techniques, each executed with varying lower-limb involvement: foot-up (FU), foot-back (FB), and minimal leg drive (ARM), as performed by 12 high-performance male players were recorded using a 12-camera Vicon MX motion analysis system operating at 250 Hz. A discriminant analysis determined the lower-limb kinematics that distinguished serve technique, and by extension, leg drive. A total of 18 one-way ANOVA ascertained statistically significant differences in the kinematic and kinetic variables considered to relate to or represent shoulder joint loading in FU, FB, and ARM serves. RESULTS The lower-limb kinematics shown to best discriminate between service techniques were range of rear and front knee joint extension, and peak angular velocity of rear knee joint extension. The forward swings of the FU (43.6 +/- 3.0 m.s(-1), P < 0.05) and FB (42.6 +/- 3.1 m.s(-1), P < 0.05) techniques were characterized by higher peak racket speeds than those generated in the ARM (39.4 +/- 3.4 m.s(-1)) serve. Regardless of stance and leg drive, similar pre- and post-impact shoulder joint kinetics were developed. CONCLUSION Knowledge of a servers range of front and rear knee joint extension as well as his/her peak angular velocity of rear knee joint extension is sufficient to ascertain the stance and quality of leg drive used. When facilitated by a leg drive, high-performance players generate similar resultant pre-impact racket velocities independent of stance. With no leg drive, players develop lower resultant racket velocities. Comparable shoulder joint kinetics, however, evolved from the differential lower-limb mechanics that characterized the FU, FB, and ARM techniques.

Repeatability of upper limb kinematics for children with and without cerebral palsy

BACKGROUND There is increasing demand for a standardised and reliable protocol for the objective assessment of upper limb motion in clinical populations. This paper describes the repeatability of a three-dimensional (3D) kinematic model and protocol to assess upper limb movement for children with and without cerebral palsy (CP). METHODS Ten typically developing (TD) children (m=10.5years+/-1.18) and seven children with CP (spastic hemiplegia) (m=11.14years+/-1.86) completed upper limb motion analysis on two occasions separated by at least one week. Participants performed three trials of four functional tasks, where 3D joint angles were calculated at the thorax, shoulder, elbow and wrist. Within and between-day repeatability was assessed using coefficients of multiple determination (CMD). FINDINGS There were distinct kinematic patterns for both groups for each functional task. In relation to their peers, children with CP consistently displayed reduced elbow extension, and compensatory patterns at the shoulder and thorax. High within and between-day CMD scores were revealed for specific rotations, with the highest being obtained at joints with large ranges of motion. INTERPRETATION The chosen tasks delineate the upper limb kinematic patterns of those with and without CP. The model has high within and between-day repeatability particularly where joint rotations demonstrate a large range of movement. 3D motion analysis is a feasible assessment tool for use with clinical populations.

Joint kinetics in rearfoot versus forefoot running: Implications of switching technique

PURPOSE To better understand the mechanical factors differentiating forefoot and rearfoot strike (RFS) running, as well as the mechanical consequences of switching techniques, we assessed lower limb joint kinetics in habitual and imposed techniques in both groups. METHODS All participants performed both RFS and forefoot strike (FFS) techniques on an instrumented treadmill at 4.5 m·s while force and kinematic data were collected. RESULTS Total (sum of ankle, knee, and hip) lower limb work and average power did not differ between habitual RFS and FFS runners. However, moments, negative work and negative instantaneous and average power during stance were greater at the knee in RFS and at the ankle in FFS techniques. When habitual RFS runners switched to an imposed FFS, they were able to replicate the sagittal plane mechanics of a habitual FFS; however, the ankle internal rotation moment was increased by 33%, whereas the knee abduction moments were not reduced, remaining 48.5% higher than a habitual FFS. In addition, total positive and negative lower limb average power was increased by 17% and 9%, respectively. When habitual FFS runners switched to an imposed RFS, they were able to match the mechanics of habitual RFS runners with the exception of knee abduction moments, which remained 38% lower than a habitual RFS and, surprisingly, a reduction of total lower limb positive average power of 10.5%. CONCLUSIONS There appears to be no clear overall mechanical advantage of a habitual FFS or RFS. Switching techniques may have different injury implications given the altered distribution in loading between joints but should be weighed against the overall effects on limb mechanics; adopting an imposed RFS may prove the most beneficial given the absence of any clear mechanical performance decrements.

The off-break and “doosra”: Kinematic variations of elite and sub-elite bowlers in creating ball spin in cricket bowling

This study sought to identify kinematic differences in finger-spin bowling actions required to generate variations in ball speed and spin between different playing groups. A 12-camera Vicon system recorded the off-spin bowling actions of six elite and 13 high-performance spin bowlers, and the “doosra” actions of four elite and two high-performance players. Forearm abduction and fixed elbow flexion in the bowling arm were higher for the elite players compared with the high-performance players. The elite bowlers when compared with the high-performance players delivered the off-break at a statistically significant higher velocity (75.1 and 67.1 km/hr respectively) and with a higher level of spin (26.7 and 22.2 rev/s respectively). Large effect sizes were seen between ball rotation, pelvic and shoulder alignment rotations in the transverse plane. Elbow extension was larger for elite bowlers over the period upper arm horizontal to ball release. Compared to the off-break, larger ranges of shoulder horizontal rotation, elbow and wrist extension were evident for the “doosra”. Furthermore, the “doosra” was bowled with a significantly longer stride length and lower ball release height. Although not significantly different, moderate to high effect size differences were recorded for pelvis rotation, elbow extension and elbow rotation ranges of motion.

MRI development and validation of two new predictive methods of glenohumeral joint centre location identification and comparison with established techniques.

Identification of the centre of the glenohumeral joint (GHJ) is essential for three-dimensional (3D) upper limb motion analysis. A number of convenient, yet un-validated methods are routinely used to estimate the GHJ location in preference to the International Society of Biomechanics (ISB) recommended methods. The current study developed a new regression model, and simple 3D offset method for GHJ location estimation, employing easy to administer measures, and compared the estimates with the known GHJ location measured with magnetic resonance imaging (MRI). The accuracy and reliability of the new regression and simple 3D offset techniques were compared with six established predictive methods. Twenty subjects wore a 3D motion analysis marker set that was also visible in MRI. Immediately following imaging, they underwent 3D motion analysis acquisition. The GHJ and anatomical landmark positions of 15 participants were used to determine the new regression and simple 3D generic offset methods. These were compared for accuracy with six established methods using 10 subjects data. A cross validation on 5 participants not used for regression model development was also performed. Finally, 10 participants underwent a further two MRIs and subsequent 3D motion analysis analyses for inter-tester and intra-tester reliability quantification. When compared with any of the other established methods, our newly developed regression model found an average GHJ location closer to the actual MRI location, having an GHJ location error of 13+/-2 mm, and had significantly lower inter-tester reliability error, 6+/-4 mm (p<0.01).

Neuromuscular adaptations to eccentric strength training in children and adolescents with cerebral palsy.

Aim  To determine the neuromuscular outcomes of an eccentric strength‐training programme for children and adolescents with cerebral palsy (CP).

The Foot’s Arch and the Energetics of Human Locomotion

The energy-sparing spring theory of the foot’s arch has become central to interpretations of the foot’s mechanical function and evolution. Using a novel insole technique that restricted compression of the foot’s longitudinal arch, this study provides the first direct evidence that arch compression/recoil during locomotion contributes to lowering energy cost. Restricting arch compression near maximally (~80%) during moderate-speed (2.7 ms−1) level running increased metabolic cost by + 6.0% (p < 0.001, d = 0.67; unaffected by foot strike technique). A simple model shows that the metabolic energy saved by the arch is largely explained by the passive-elastic work it supplies that would otherwise be done by active muscle. Both experimental and model data confirm that it is the end-range of arch compression that dictates the energy-saving role of the arch. Restricting arch compression had no effect on the cost of walking or incline running (3°), commensurate with the smaller role of passive-elastic mechanics in these gaits. These findings substantiate the elastic energy-saving role of the longitudinal arch during running, and suggest that arch supports used in some footwear and orthotics may increase the cost of running.

Laboratory versus field testing in cricket bowling: A review of current and past practice in modelling techniques

In cricket bowling, the reconstruction of elbow angle data is of utmost importance to the bowling versus throwing argument. This paper reviews system and modelling errors inherent in three-dimensional reconstruction processes with respect to the elbow extension tolerance set by the International Cricket Council. An understanding of these factors will enable more informed decisions about the choice of in-field versus laboratory testing in the calculation of elbow extension during bowling in cricket. Although there is a paucity of objective data related to in-field and laboratory testing, biomechanists must be guided by the greater accuracy of opto-reflective than video-based systems and so testing, at least for the present, should be conducted in a laboratory setting.

The lumbar spine of the young cricket fast bowler: An MRI study

OBJECTIVES To describe the prevalence and nature of lumbar spinal abnormalities in adolescent cricket fast bowlers. DESIGN Observational study. METHODS 46 asymptomatic fast bowlers aged 13-18 years participated in the study and were grouped into under-15 (U15), under-17 (U17) and under-19 (U19) classifications. All participants underwent magnetic resonance imaging of the lumbar spine and abnormalities of the pars interarticularis and intervertebral discs were graded according to type and severity. Other abnormalities were also noted. RESULTS Fifteen bowlers (33%) had at least one pars interarticularis abnormality. Six bilateral and 10 unilateral defects were identified. Of the 10 unilateral pars abnormalities, 6 occurred on the non-dominant side. Nineteen of the abnormalities occurred at the L5 vertebral level, 2 at L4 and 1 at L3. The most common type of pars abnormality was the subtotal stress fracture, which was found in 38% of bowlers aged 16 years and under. Sixteen participants (35%) were found to have degeneration of at least 1 lumbar disc and the prevalence increased with each successive age group (29% U15, 33% U17 and 43% U19). Of the 25 discs with signs of degeneration, 9 occurred at L4/5 and 7 at L5/S1. Eleven of these were classified as mild degeneration, 13 as moderate, and 1 as severe. Disc bulges were found in 33% of participants. CONCLUSIONS Lumbar radiological abnormalities are common in asymptomatic adolescent fast bowlers. Acute bone stress reactions of the lumbar pars interarticularis are visible on magnetic resonance imaging and, in some instances, occur before the onset of activity-related pain.

Lycra arm splints in conjunction with goal-directed training can improve movement in children with cerebral palsy

OBJECTIVES To investigate the effects of lycra® arm splint wear on goal attainment and three dimensional (3D) kinematics of the upper limb and trunk in children with cerebral palsy (CP). DESIGN Randomised clinical trial whereby participants were randomised to parallel groups with waiting list control. PARTICIPANTS Sixteen children with CP (hypertonia) aged 9 to 14 years. INTERVENTION Three months lycra arm splint wear combined with goal directed training. MAIN OUTCOME MEASURE Goal attainment scale, and 3D upper limb and trunk kinematics across four upper limb movement tasks. RESULTS 17/18 children achieved their movement goals following three months of splinting. Selected joint kinematics improved on immediate splint application. Further improvements in joint kinematics were demonstrated following 3 months of splint wear, particularly in elbow extension, shoulder flexion and abduction and in thorax flexion. Only improvements in movement compensations at the thorax remained following removal of the splint. CONCLUSIONS The lycra® arm splint, made a quantifiable change to the attainment of movement goals of importance to the child. Furthermore, improvements were demonstrated in selected maximum range of movement and joint kinematics during functional tasks at the elbow and shoulder joints and thorax segment in children with CP.