Kinetics of Hula Kinetics of Hula Hooping: Hooping:

An Exploratory AnalysisAn Exploratory AnalysisTyler Cluff Tyler Cluff

D. Gordon E. RobertsonD. Gordon E. RobertsonRamesh BalasubramaniamRamesh Balasubramaniam

School of Human Kinetics School of Human Kinetics Faculty of Health SciencesFaculty of Health Sciences

University of Ottawa, Ottawa, CanadaUniversity of Ottawa, Ottawa, Canada

Hula HoopHula Hoop

Physics of Hula HoopingPhysics of Hula Hooping

Conservation of angular momentumConservation of angular momentum Small, carefully initiated impulses Small, carefully initiated impulses

exerted on the interior periphery of exerted on the interior periphery of hoophoop

Vertical component to oppose gravityVertical component to oppose gravity Dynamic equilibrium achieved by Dynamic equilibrium achieved by

coupled, sustained oscillations about coupled, sustained oscillations about joints of lower extremityjoints of lower extremity

Previous ResearchPrevious Research Balasubramaniam and Turvey (2004):Balasubramaniam and Turvey (2004):

– 95% variance accommodated by just two modes95% variance accommodated by just two modes

– in the large hoop condition, the first mode was a in the large hoop condition, the first mode was a hip dynamical system; fore-aft motion of the hips hip dynamical system; fore-aft motion of the hips maintained rotational motionmaintained rotational motion

– the second eigenvalue was a knee dynamical the second eigenvalue was a knee dynamical systemsystem

– larger hoop size required more emphasis on the larger hoop size required more emphasis on the role of the knees to maintain motion of the role of the knees to maintain motion of the vertical regulatory componentvertical regulatory component

PurposePurpose

The purpose of this research was to The purpose of this research was to compare the conclusions reached using compare the conclusions reached using dynamical systems theory with those of dynamical systems theory with those of inverse dynamics/moment power inverse dynamics/moment power analyses.analyses.

Are the two theories in agreement with Are the two theories in agreement with regards to the involvement of the hips and regards to the involvement of the hips and knees in maintaining oscillatory motion of knees in maintaining oscillatory motion of the hoop?the hoop?

Methods Flow ChartMethods Flow Chartthree female participants

5 x 30 s trials at resonant frequency with small hoop (70 cm)

Vicon Workstation:

5 MX13 cameras (200 Hz)

2 Kistler force platforms

22 marker trajectories

Visual3D v3.79:

7 segment model

Inverse dynamics and moment powers

ResultsResults

• each figure shows three repetitions averaged across five trials (error bars are ± 1 SD)

• vertical axes are normalized to body mass

• top curves are hip, middle are knee, bottom are ankle

• left side data are from the left limb and vice versa

• each figure shows three repetitions averaged across five trials (error bars are ± 1 SD)

• vertical axes are normalized to body mass

• top curves are hip, middle are knee, bottom are ankle

• left side data are from the left limb and vice versa

Results – hip ab/adductor Results – hip ab/adductor momentsmoments

Figure 1. Ab/adductor moments of the ankle, knee and hip joints (Subject 1).

• hip abductors dominated throughout

• left and right sides were 180 degrees out-of-phase

• adductors performed minor role and little work

• hip abductors dominated throughout

• left and right sides were 180 degrees out-of-phase

• adductors performed minor role and little work

Results – ab/adductor powersResults – ab/adductor powers

Figure 2. Abductor/adductor powers of the ankle, knee and hip joints (Subject 1).

• all subjects had similar patterns of the hip abductors and adductors

• work done at knee was likely not muscular but was likely done by joint structures

• little or no work done at ankles

• all subjects had similar patterns of the hip abductors and adductors

• work done at knee was likely not muscular but was likely done by joint structures

• little or no work done at ankles

Results – ab/adductor powersResults – ab/adductor powers

Figure 2. Abductor/adductor powers of the ankle, knee and hip joints (Subject 1).

• hip abductors produced negative work

• immediately afterwards positive work (prestretching?)

• followed by a brief pause or adductor work while contralateral abductors performed positive work

• hip abductors produced negative work

• immediately afterwards positive work (prestretching?)

• followed by a brief pause or adductor work while contralateral abductors performed positive work

S1 Results – knee extensor S1 Results – knee extensor strategystrategy

Figure 3. Flexor/extensor moments of the ankle, hip and knee (Subject 1).

• knee extensors dominated throughout

• left and right sides out-of-phase

• ankle plantiflexors also contributed

• knee extensors dominated throughout

• left and right sides out-of-phase

• ankle plantiflexors also contributed

S1 Results – knee extensor S1 Results – knee extensor strategystrategy

Figure 4. Flexor/extensor powers of the ankle, hip and knee (Subject 1).

• knee extensors produced positive then negative work

• while left side did positive work, right did negative work

• little work by plantiflexors or hip moments

• knee extensors produced positive then negative work

• while left side did positive work, right did negative work

• little work by plantiflexors or hip moments

S2 Moments – hip-ankle S2 Moments – hip-ankle strategystrategy

Figure 5. Flexor/extensor moments of the ankle, knee and hip joints (Subject 2).

• hip and knee flexors and extensors are involved

• ankle plantiflexors dominated throughout

• hip and knee flexors and extensors are involved

• ankle plantiflexors dominated throughout

S2 Powers – hip-ankle strategyS2 Powers – hip-ankle strategy

Figure 6. Flexor/extensor powers of the ankle, knee and hip joints (Subject 2).

• hip flexors and plantiflexors of left side produced the majority of the positive work; right hip extensors assisted

• little work by knee moments

• hip flexors and plantiflexors of left side produced the majority of the positive work; right hip extensors assisted

• little work by knee moments

S3 Moments – whole leg S3 Moments – whole leg strategystrategy

Figure 7. Flexor/extensor moments of the ankle, knee and hip joints (Subject 3).

• similar to subject 2 but both sides produced equal magnitudes

• both sides were only slightly out of phase

• similar to subject 2 but both sides produced equal magnitudes

• both sides were only slightly out of phase

S3 Powers – whole leg strategyS3 Powers – whole leg strategy

Figure 8. Flexor/extensor powers of the ankle, knee and hip joints (Subject 3).

• left knee flexors & extensors and plantiflexors provided most work with assistance from both hip flexors

• right knee extensors and plantiflexors provided negative work

• left knee flexors & extensors and plantiflexors provided most work with assistance from both hip flexors

• right knee extensors and plantiflexors provided negative work

SummarySummary All subjects used the hip abductors to maintain hoop All subjects used the hip abductors to maintain hoop

rotational equilibriumrotational equilibrium With same experimental conditions each subject With same experimental conditions each subject

adopted a different strategy to maintain hoop’s adopted a different strategy to maintain hoop’s vertical equilibriumvertical equilibrium

Subject 1 relied on the knee extensorsSubject 1 relied on the knee extensors Subject 2 relied on the hip moments and ankle Subject 2 relied on the hip moments and ankle

plantiflexorsplantiflexors Subject 3 incorporating the flexors/extensors of Subject 3 incorporating the flexors/extensors of

the knee and hip and ankle plantiflexorsthe knee and hip and ankle plantiflexors Agreement between dynamical systems theory and Agreement between dynamical systems theory and

inverse dynamics/moment power analyses but in inverse dynamics/moment power analyses but in unpredictable waysunpredictable ways

Care must be taken when averaging subjects togetherCare must be taken when averaging subjects together

Questions?Questions?