When reporting a subject’s mean movement pattern, it is important to ensure that reported values are representative of the subject’s typical movement. While previous studies have used the mean of 3 trials, scientific justification of this number is lacking. One approach is to determine statistically how many trials are required to achieve a representative mean. This study compared 4 methods of calculating the number of trials required in a hopping movement to achieve a representative mean. Fifteen males completed 15 trials of a lateral hurdle hop. Range of motion at the trunk, pelvis, hip, knee, and ankle, in addition to peak moments for the latter 3 joints were examined. The number of trials required was computed using a peak intraclass correlation coefficient method, sequential analysis with a bandwidth of acceptable variance in the mean, and a novel method based on the standard error of measurement (SEMind). The number of trials required across all variables ranged from 2 to 12 depending on method, joint, and anatomical plane. The authors advocate the SEMind method as it demonstrated fewer limitations than the other methods. Using the SEMind, the required number of trials for a representative mean during the lateral hurdle hop is 6.
Shane J. Gore, Brendan M. Marshall, Andrew D. Franklyn-Miller, Eanna C. Falvey and Kieran A. Moran
Ram Haddas, Steven F. Sawyer, Phillip S. Sizer, Toby Brooks, Ming-Chien Chyu and C. Roger James
Recurrent lower back pain (rLBP) and neuromuscular fatigue are independently thought to increase the risk of lower extremity (LE) injury. Volitional preemptive abdominal contraction (VPAC) is thought to improve lumbar spine and pelvis control in individuals with rLBP. The effects of VPAC on fatigued landing performance in individuals with rLBP are unknown.
To determine the effects of VPAC and LE fatigue on landing performance in a rLBP population.
Cross-sectional pretest-posttest cohort control design.
A clinical biomechanics laboratory.
32 rLBP (age 21.2 ± 2.7 y) but without current symptoms and 33 healthy (age 20.9 ± 2.3 y) subjects.
(i) Volitional preemptive abdominal contraction using abdominal bracing and (ii) fatigue using submaximal free-weight squat protocol with 15% body weight until task failure was achieved.
Main Outcome Measure(s):
Knee and ankle angles, moments, electromyographic measurements from semitendinosus and vastus medialis muscles, and ground reaction force (GRF) were collected during 0.30 m drop-jump landings.
The VPAC resulted in significantly earlier muscle onsets across all muscles with and without fatigue in both groups (mean ± SD, 0.063 ± 0.016 s earlier; P ≤ .001). Fatigue significantly delayed semitendinosus muscle onsets (0.033 ± 0.024 s later; P ≤ .001), decreased GRF (P ≤ .001), and altered landing kinematics in a variety of ways. The rLBP group exhibited delayed semitendinosus and vastus medialis muscle onsets (0.031 ± 0.028 s later; P ≤ .001) and 1.8° less knee flexion at initial contact (P ≤ .008).
The VPAC decreases some of the detrimental effects of fatigue on landing biomechanics and thus may reduce LE injury risk in a rLBP population.
Sébastien Viel, Marianne Vaugoyeau and Christine Assaiante
In the current study, we adopted the hypothesis that the body scheme disturbances occurring during adolescence might lead subjects to transiently neglect proprioceptive information and that adolescents might rely more strongly on vision to control their orientation and stabilize their body. To check this point, we asked adolescents 14–15 years to maintain vertical stance while very slow sinusoidal oscillations in the frontal plane were applied to the supporting platform at 0.01 Hz (below the detection threshold of the semicircular canal system) and at 0.06 Hz (above) with the eyes open and closed. Two postural components, orientation and segmental stabilization, were analyzed at the head, shoulder, trunk, and pelvis levels. At the lowest frequency without vision, the performances of adolescents were much less efficient than those of adults. Moreover, this study showed that vision plays a predominant role in adolescents’ control of orientation and body stabilization. At 0.06 Hz without vision, a clearcut difference was observed between the strategies used by girls and boys; specifically, the maturation of the segmental stabilization processes was found to be more advanced in girls than in boys. However, no such difference was observed at 0.01 Hz. Lastly, comparisons between the data obtained in adolescents and those previously obtained in young adults (Vaugoyeau, Viel, Amblard, Azulay, & Assaiante, 2008) clearly show that adolescents use different postural strategies and that they are not yet capable of reaching comparable postural performance levels to those observed in adults. Because adolescents were not able to use the proprioceptive information available to improve their postural control, we concluded that they showed a maturational lag in comparison with adults. This suggests that the mechanisms underlying postural control are still maturing during adolescence, which might constitute a transient period of proprioceptive neglect in sensory integration of postural control.
Leanne Sawle, Jennifer Freeman and Jonathan Marsden
Context: Athletic pelvic/groin pain is a common yet often challenging problem to both diagnose and manage. A new tool has been developed based on the clinical effects of applied force on the pelvis. Early findings indicate that this customized compression orthosis may have a positive effect on pelvic/groin pain and performance measures. Objectives: To inform the design and test the practicality of procedures for a future definitively powered randomized controlled trial and to provide an estimate of the effect size of this orthosis on selected clinical and performance measures. Design: Pilot randomized controlled trial with participants randomly allocated to an intervention or waiting-list control group. Setting: The training location of each athlete. Participants: 24 athletes with subacute and chronic pelvic conditions were proposed to be recruited. Intervention: A customized compression orthosis, delivering targeted compression to the pelvic girdle. Outcome Measures: Measures were the active straight leg raise (ASLR) test, squeeze test, broad jump, and the multiple single-leg hop-stabilization test. Results: A total of 16 athletes completed the study. The invention group demonstrated moderate to large estimated effect sizes on the squeeze test and active straight leg raise tests (d = 0.6–1.1) while wearing the orthosis. Small effect sizes (d = 0.2) were seen on jump distance and the dominant leg balance score. Compared with the control group, the intervention group also showed moderate to large estimated effect sizes on the active straight leg raise measures (d = 0.5–0.9) when wearing sports shorts. Conclusions: The protocol was feasible. Effect sizes and recruitment/attrition rates suggest that the intervention holds promise and that a future definitively powered randomized controlled trial appears feasible and is indicated.
Yuta Koshino, Tomoya Ishida, Masanori Yamanaka, Mina Samukawa, Takumi Kobayashi and Harukazu Tohyama
Identifying the foot positions that are vulnerable to lateral ankle sprains is important for injury prevention. The effects of foot position in the transverse plane on ankle biomechanics during landing are unknown.
To examine the effects of toe-in or toe-out positioning on ankle inversion motion and moment during single-leg landing.
Motion analysis laboratory.
18 healthy participants (9 men and 9 women).
Participants performed single-leg landing trials from a 30-cm high box under 3 conditions: natural landing, foot internally rotated (toe-in), and foot externally rotated (toe-out).
Main Outcome Measures:
4 toe-in or toe-out angles were calculated against 4 reference coordinates (laboratory, pelvis, thigh, and shank) in the transverse plane. Ankle inversion angle, angular velocity, and external moment in the 200 ms after initial foot-to-ground contact were compared between the 3 landing conditions.
All toe-in or toe-out angles other than those calculated against the shank were significantly different between each of the 3 landing conditions (P < .001). Ankle inversion angle, angular velocity, and moment were highest during toe-in landings (P < .01), while eversion angle and moment were highest during toe-out landings (P < .001). The effect sizes of these differences were large. Vertical ground reaction forces were not different between the 3 landing conditions (P = .290).
Toe-in or toe-out positioning during single-leg landings impacts on ankle inversion and eversion motion and moment. Athletes could train not to land with the toe-in positioning to prevent lateral ankle sprains.
Rafael F. Escamilla, Glenn S. Fleisig, Coop DeRenne, Marcus K. Taylor, Claude T. Moorman III, Rodney Imamura, Edward Barakatt and James R. Andrews
We propose that learning proper hitting kinematics should be encouraged at a young age during youth baseball because this may help reinforce proper hitting kinematics as a player progresses to higher levels of baseball in their adult years. To enhance our understanding between youth and adult baseball hitting, kinematic and temporal analyses of baseball hitting were evaluated with a high-speed motion analysis system between 12 skilled youth and 12 skilled adult baseball players. There were only a small number of temporal differences between youth and adult hitters, with adult hitters taking significantly greater time than youth hitters during the stride phase and during the swing. Compared with youth hitters, adult hitters a) had significantly greater (p < .01) lead knee flexion when the hands started to move forward; b) flexed the lead knee over a greater range of motion during the transition phase (31° versus 13°); c) extended the lead knee over a greater range of motion during the bat acceleration phase (59° versus 32°); d) maintained a more open pelvis position at lead foot off ground; and e) maintained a more open upper torso position when the hands started to move forward and a more closed upper torso position at bat-ball contact. Moreover, adult hitters had greater peak upper torso angular velocity (857°/s versus 717°/s), peak left elbow extension angular velocity (752°/s versus 598°/s), peak left knee extension angular velocity (386°/s versus 303°/s), and bat linear velocity at bat-ball contact (30 m/s versus 25 m/s). The numerous differences in kinematic and temporal parameters between youth and adult hitters suggest that hitting mechanics are different between these two groups.
Niels J. Nedergaard, Mark A. Robinson, Elena Eusterwiemann, Barry Drust, Paulo J. Lisboa and Jos Vanrenterghem
To investigate the relationship between whole-body accelerations and body-worn accelerometry during team-sport movements.
Twenty male team-sport players performed forward running and anticipated 45° and 90° side-cuts at approach speeds of 2, 3, 4, and 5 m/s. Whole-body center-of-mass (CoM) accelerations were determined from ground-reaction forces collected from 1 foot–ground contact, and segmental accelerations were measured from a commercial GPS accelerometer unit on the upper trunk. Three higher-specification accelerometers were also positioned on the GPS unit, the dorsal aspect of the pelvis, and the shaft of the tibia. Associations between mechanical load variables (peak acceleration, loading rate, and impulse) calculated from both CoM accelerations and segmental accelerations were explored using regression analysis. In addition, 1-dimensional statistical parametric mapping (SPM) was used to explore the relationships between peak segmental accelerations and CoM-acceleration profiles during the whole foot–ground contact.
A weak relationship was observed for the investigated mechanical load variables regardless of accelerometer location and task (R 2 values across accelerometer locations and tasks: peak acceleration .08–.55, loading rate .27–.59, and impulse .02–.59). Segmental accelerations generally overestimated whole-body mechanical load. SPM analysis showed that peak segmental accelerations were mostly related to CoM accelerations during the first 40–50% of contact phase.
While body-worn accelerometry correlates to whole-body loading in team-sport movements and can reveal useful estimates concerning loading, these correlations are not strong. Body-worn accelerometry should therefore be used with caution to monitor whole-body mechanical loading in the field.
Noah X. Tocci, David R. Howell, Dai Sugimoto, Corey Dawkins, Amy Whited and Donald Bae
-related injury. 9 , 11 , 18 Lower extremity movement, in particular pelvis movement, is one fundamental aspect to proper pitching mechanics. 9 , 19 , 20 Specifically, the pelvis acts as the foundation to the throwing motion, and serves an integral role in the transfer of energy during a pitch. 21
Nicole C. George, Charles Kahelin, Timothy A. Burkhart and David M. Andrews
anatomical landmarks Measurements Segment Description and landmarks Lengths Pelvis (A) Vertical distance between the pubic symphysis and the level of the most prominent ridge on the superior aspect of the iliac crest Pelvis (L) ‡ Vertical distance between the
Erin Macaronas, Shannon David and Nicole German
or effusion”, and “chronic expanding hematoma.” 1 Morel-Lavallée lesions are most commonly a result of severe trauma occurring at the greater trochanter and other parts of the pelvis. 1 – 3 Although the greater trochanter is the most common location for Morel-Lavallée lesions to occur, cases of the