Yo Shih - University of Southern California, USA
The International Society of Biomechanics’ Matching Dissertation Grant supported my dissertation which investigates the neural correlates associated with lower extremity movement behavior.
Various knee injuries such as patellofemoral pain and anterior cruciate ligament injuries have been linked to a lower extremity movement pattern that favors use of the knee extensors relative to the hip extensors. Insufficient strength of the hip extensors relative to the knee extensors has been proposed to underlie this high-risk biomechanical strategy, however muscle strength only explains a small amount of the variance (17%) in this movement pattern (Stearns et al., 2013).
Apart from diminished strength, altered motor control has been suggested to underlie high-risk lower extremity movement patterns. Centrally-mediated control factors influence how the muscle is used and can be probed by testing the excitability of the corticomotor pathway for a specific muscle (Fisher et al., 2013). This is done by measuring the amplitude of evoked potentials produced in the muscle by transcranial magnetic stimulation (TMS). Although TMS has been used to study upper extremity muscles, there is little research examining the relationship between corticomotor excitability (CME) and lower extremity biomechanics. To date, the association between corticomotor control and movement impairments related to knee injury is unknown. Therefore, the purpose of the current study was to determine the association between 1) CME of gluteus maximus (GM) and the hip extensor strength, and 2) CME of GM and the use of hip extensor (measured by average hip extensor moment) during single-leg drop jump.
Thirty-two healthy individuals (17 females, 15 males) participated. The slope of the input-output curve obtained from transcranial magnetic stimulation was used to assess CME of GM. The maximal hip extensor torque during maximal voluntary isometric contraction (MVIC) was used to represent hip extensor strength. The averaged hip extensor moment during the stance phase of the single-leg drop jump was calculated to represent the use of hip extensors.
A significant positive correlation between CME of GM and hip extensor strength (r = 0.6, p<0.001) was found. Also, the CME of GM is significantly correlated to the average hip extensor moment during the single-leg drop jump (r = 0.44, p= 0.01). These findings suggest that the hip extensor strength and the use of the hip extensors during single-leg drop jump are associated with the strength of the descending neural drive along the corticomotor pathway of GM. The altered motor control of the GM may play a role in movement behavior thought to be contributory to knee injury.
I fully appreciate the International Society of Biomechanics for the support of this dissertation.
Jodie Willis - Macquarie University, Australia
I would like to thank the ISB council members for awarding me the matching dissertation grant to assist with my PhD research that is investigating sex-specific biomechanical and neuromuscular adaptations to targeted 10-week physical training programs for Military load-carriage.
My first study involved recruiting a male-only population who could meet Australian Army basic fitness assessment requirements. Various physical performance measures including strength, power, physiological, and psychophysiology responses were collected to enable the assessment of adaptive responses to load carriage training. We found that the lower- limb specific training program elicited positive physical performance improvements and physiological adaptations. These results were presented at my first international conference at International Society of Biomechanics in Sport 2018 in Auckland, New Zealand. Further findings included kinematic variations and adaptive responses in gait over time; these were presented at Australasian Biomechanics Conference (ABC11). Presenting at these conferences were fantastic experiences that allowed me to gain valuable feedback from other researchers in the field and allowed me to reflect on my research for future studies. I was also able to present load carriage task psychophysiological findings at the 2018 Australian Strength and Conditioning Association (ASCA) International Conference. This was a great opportunity to network and present among applied practitioners working in both tactical and professional athlete environments.
My second PhD study has already commenced and replicates the male study with a female- only population. Physical performance and biomechanical data will be compared with male results to identify sex-specific responses to physical training. Analysis has so far shown that females appear to respond similarly to males through positive physical performance adaptations after 10-weeks of specific training. Data from both these studies have been submitted in three abstracts for presentations at ISB/ASB 2019. Later this year I am looking forward to starting my third and final PhD study. This research will will aim to identify if there is a specific physical training program that will optimise load carriage performance in female soldiers.
I would like to again thank ISB for this award as it helped to enrich my research and has contributed to the opportunities that I have experienced throughout my PhD so far. I look forward to presenting at ISB/ASB 2019!
Emily Gerstle - University of Wisconsin-Milwaukee
Transition step mechanics: how influential are age and fall risk?
As age increases, so does the risk of fall related injuries. Older adults (65 and older) fall, most often during locomotion and almost twice as often as middle-aged adults [2]. Older adult women specifically fall twice as often as men and incur almost three times the medical costs for treatment of fall related injuries [3]. One of the most hazardous types of locomotion for older adults is step negotiation. In fact, steps or curbs account for the second most common activity during which falls take place in older adults [4]. Further, the rate of injury due to falls during step negotiation is 12% greater than that during level walking, the most common activity during which falls occur [5]. The most commonly reported causes of falls on steps are errors in step clearance (e.g. catching the heel on the edge of the stair) or misplacing the foot on the step (e.g. over or under stepping) [6]. However, results of previous studies examining older adults during step negotiation have been inconsistent.
The purpose of this study was to identify modifiable lower extremity mechanical factors associated with transition step clearance and landing in young women, older women with no fall history, and older women with a history of falls.
Specifically examined were:
- Lead and trail limb minimum vertical step clearance and horizontal displacement from step
- Bilateral kinematics (hip, knee, ankle) during each foot minimum clearance
- Lead limb distal foot kinematics at initial contact and during weight acceptance
Currently data collection and data processing are underway. Many thanks to the ISB for supporting this research; I look forward to sharing the results at the XXVII ISB Congress in Calgary.
References:
- Lee, H.J. and L.S. Chou. J Biomech, 2007. 40(11): p. 2530-6.
- Skalska, A., et al. Exp Gerontol, 2013. 48(2): p. 140-6.
- Burns, E.R., et al. J Safety Res, 2016. 58: p. 99-103.
- Koepsell, T.D., et al. J Am Geriatr Soc, 2004. 52(9): p. 1495-501.
- Duckham, R.L., et al. BMC Geriatrics, 2013. 13(1): p. 133.
- Templer, J. The staircase. 1992, MIT Press.
