Thread by @sciofmultispeed, Following on from our new paper on antepenultimate, penultimate and final foot [...]

Following on from our new paper on antepenultimate, penultimate and final foot contacts during 180-degree turns published in @JSportsSci

https://www.researchgate.net/publication/348068717_How_early_should_you_brake_during_a_180_turn_A_kinetic_comparison_of_the_antepenultimate_penultimate_and_final_foot_contacts_during_a_505_change_of_direction_speed_test

https://www.tandfonline.com/doi/full/10.1080/02640414.2020.1823130

Here’s some background to the study, what we did it, and what we found...

[THREAD]

Change of direction (CoD) is a fundamental quality of field and court sports, and also forms the mechanical and physical basis underpinning agility. Therefore, it seems apparent to both assess and develop one’s CoD abilities in their respective sport(s).

https://journals.lww.com/nsca-scj/fulltext/2018/02000/change_of_direction_and_agility_tests__challenging.4.aspx

Though not as frequent as 0-90 degrees, turns of 90-180 degrees are commonly performed in soccer, and are also important for sports such as

this, understanding the kinetic demands of these tasks warrants further investigation.

https://eprints.qut.edu.au/204875/

Though not as frequent as 0-90 degrees, turns of 90-180 degrees are commonly performed in soccer, and are also important for sports such as this, understanding the kinetic demands of these tasks warrants further investigation. https://eprints.qut.edu.au/204875/

Also, turning strategies may differ between planned (CoD) and unplanned (agility) tasks, therefore assessment and monitoring of (ideally) both methods would be of benefit to athlete monitoring programmes.

https://www.researchgate.net/profile/Paul_Jones10/publication/280923425_A_comparison_of_braking_characteristics_between_pre-planned_and_unanticipated_changing_direction_tasks_in_female_soccer_players_An_exploratory_study/links/57874a9908aec5c2e4e531d1.pdf

CoD can be described as a 4-step process:

initial acceleration

deceleration

foot plant

reacceleration

Based on this concept CoD can be classed as a multi-step action to facilitate effective deceleration, redirection and reacceleration.

https://commons.nmu.edu/cgi/viewcontent.cgi?article=1394&=&context=isbs&=&sei-redir=1&referer=https%253A%252F%252Fscholar.google.com%252Fscholar%253Fhl%253Den%2526as_sdt%253D0%25252C5%2526q%253DGraham%252Bsmith%252Bdeceleration%2526oq%253DGraham%252Bsmith%252Bdecelera#search=%22Graham%20smith%20deceleration%22

CoD can be described as a 4-step process: initial acceleration deceleration foot plant reaccelerationBased on this concept CoD can be classed as a multi-step action to facilitate effective deceleration, redirection and reacceleration. https://commons.nmu.edu/cgi/viewcontent.cgi?article=1394&=&context=isbs&=&sei-redir=1&referer=https%253A%252F%252Fscholar.google.com%252Fscholar%253Fhl%253Den%2526as_sdt%253D0%25252C5%2526q%253DGraham%252Bsmith%252Bdeceleration%2526oq%253DGraham%252Bsmith%252Bdecelera#search=%22Graham%20smith%20deceleration%22

Recently, an “angle-velocity trade-off” has been discussed, where as the intended CoD angle increases so do the deceleration requirements to effectively reduce horizontal momentum

This deceleration strategy is usually performed over several foot contacts

https://www.researchgate.net/publication/326916848_The_Effect_of_Angle_and_Velocity_on_Change_of_Direction_Biomechanics_An_Angle-Velocity_Trade-Off

The penultimate foot contact ([PFC] second to last foot contact prior to CoD) has shown to play an important role in effective braking and faster 180-degree turn performance

https://pubmed.ncbi.nlm.nih.gov/31868815/

https://pubmed.ncbi.nlm.nih.gov/27295508/

https://pubmed.ncbi.nlm.nih.gov/27379954/

https://pubmed.ncbi.nlm.nih.gov/29910402/

During 180-degree turns, athletes need to reduce their horizontal velocity of centre of mass to zero, via a series of foot contacts prior to turning.

Graham-Smith et al. (2018) found deceleration stopping distances of 6.6 m during sprints to a pre-determined point 15-m away.

This indicates steps prior to the PFC play a big role in effective deceleration.

The antepenultimate foot contact ([APFC] third to last foot contact prior to CoD) could be effective to facilitate braking & deceleration in preparation for the PFC prior to any pre-rotation

Nedergaard et al. (2014) reported greater trunk decelerations during the APFC compared to the final foot contact ([FFC] last foot contact prior to CoD) but did not examine GRF characteristics of the APFC. Therefore, this study was conducted

https://scholar.google.com/scholar?cluster=4269463816730379792&hl=en&as_sdt=0,5#d=gs_qabs&u=%23p%3DxaAaJqVU0KgJ

Nedergaard et al. (2014) reported greater trunk decelerations during the APFC compared to the final foot contact ([FFC] last foot contact prior to CoD) but did not examine GRF characteristics of the APFC. Therefore, this study was conducted https://scholar.google.com/scholar?cluster=4269463816730379792&hl=en&as_sdt=0,5#d=gs_qabs&u=%23p%3DxaAaJqVU0KgJ

20 university-level soccer players performed three 505 trials turning on the right leg.

Comparisons in GRF characteristics were made between foot contacts.

Associations were determined between APFC, PFC and FFC GRF characteristics and 505 performance.

Greater peak braking forces and mean GRFs were observed during the APFC compared to the PFC, suggesting the APFC May play a more important role in effective braking during 180-degree CoD.

Orientation of GRF towards horizontal and horizontal GRF contribution progressively increases across foot contacts.

The FFC serves two purposes: braking & propulsion, highlighting the importance of rapid force production and eccentric strength

https://bit.ly/38mNRiW

APFC GRFs in a more horizontally orientated direction were associated with faster 505 times.

mean horizontal-vertical GRF ratios for all 3 foot contacts related to faster 505 times.

So, the technical ability to apply force horizontally across APFC, PFC & FFC is

.

APFC GRFs in a more horizontally orientated direction were associated with faster 505 times. mean horizontal-vertical GRF ratios for all 3 foot contacts related to faster 505 times.So, the technical ability to apply force horizontally across APFC, PFC & FFC is .

No associations between PFC GRF characteristics and 505 times

PFC may facilitate

braking during

approach distances (5 m), while

approach distances (>10 m) attain

velocities, so

stopping distances are required with

reliance on earlier foot contacts (APFC)

No associations between PFC GRF characteristics and 505 times PFC may facilitate braking during approach distances (5 m), while approach distances (>10 m) attain velocities, so stopping distances are required with reliance on earlier foot contacts (APFC)

Ground contact times

for PFC & FFC (~0.5 s), while APFC

(~0.2 s).

As such, athletes tend to display a “dual-foot contact” on PFC & FFC to potentially reduce redirection requirements.

Ground contact times for PFC & FFC (~0.5 s), while APFC (~0.2 s).As such, athletes tend to display a “dual-foot contact” on PFC & FFC to potentially reduce redirection requirements.

Applications:

Coach strategies emphasising posteriorly-directed APFC GRFs & rapid horizontal force application across PFC & FFC

Potentially.....

APFC: deceleration & braking

PFC: braking & positioning

FFC: braking & propulsion

Limitations:

pre-planned 505

angle & velocity dependent

no joint kinetics & kinematics

turns performed off right leg only

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