Year

2012

Degree Name

Doctor of Philosophy

Department

School of Health Sciences

Abstract

BACKGROUND In girls, puberty is accompanied by the adolescent growth spurt, a large influx of oestrogen, as well as an increased risk of sustaining a non-contact anterior cruciate ligament (ACL) rupture. The rapid growth and hormonal changes experienced by girls throughout puberty are thought to play a role in this increased injury risk, contributing to altered lower limb inertial properties, ultimately affecting lower limb flexibility and strength, with the potential to influence landing biomechanics. However, the longitudinal changes in musculoskeletal structure and function, as well as oestrogen levels, in addition to the longitudinal development of landing technique throughout the adolescent growth spurt in girls, remains unclear.

THESIS AIM The primary purpose of this thesis was to investigate the longitudinal changes in musculoskeletal structure and function, as well as the oestrogen levels, during the adolescent growth spurt in girls and the influence of these changes on lower limb landing biomechanics.

METHODS Forty-six healthy girls, aged 10-13 years, were recruited for this longitudinal study based on their pubertal development (Tanner Stage II-III) and their time from peak height velocity (maturity offset; -6 to -4 months or 0 months). Participants were tested up to four times during the 12 months of their adolescent growth spurt, according to their maturity offset (Test 1: maturity offset = -6 to -4 months, Test 2: maturity offset = 0 months, Test 3: maturity offset = +4 months, Test 4: maturity offset = +8 months). During the laboratory test sessions, each participant’s anthropometric characteristics, oestrogen levels, anterior knee joint laxity, lower limb flexibility, isokinetic strength and landing biomechanics were collected and recorded. The landing task performed was a horizontal leap movement, during which ground reaction forces (1,000 Hz), lower limb electromyography (1,000 Hz) and kinematic data (100 Hz) were collected. Monthly tracking was also conducted, so as to estimate maturity offset using anthropometric data, as well as to determine monthly fluctuations in lower limb flexibility and strength.

Results from this longitudinal study were analysed and presented in four chapters (Chapter 3-6), with each chapter systematically contributing to the overall thesis aim. The primary purpose of Chapter 3 was to determine the longitudinal changes in anthropometry, anterior knee joint laxity, lower limb flexibility and strength, as well as the oestrogen levels, in pubescent girls during their growth spurt. Based on the findings from Chapter 3, the effects of variations in hamstring muscle strength (Chapter 4) and anterior knee joint laxity (Chapter 5) on the lower limb landing biomechanics of these pubescent girls were investigated. Finally, based on the longitudinal musculoskeletal changes displayed by girls in Chapter 3, the final experimental chapter of this thesis investigated the longitudinal changes in lower limb landing technique displayed by pubescent girls through their adolescent growth spurt (Chapter 6).

MAJOR CONCLUSIONS Based on the findings of this thesis it was concluded that during the adolescent growth spurt, pubescent girls display rapid growth of their lower limbs, an increase in anterior knee laxity, as well as a lag in the development of their hamstring muscle strength relative to their quadriceps muscle strength. The combination of these rapid and differential musculoskeletal structural and functional changes are thought to decrease knee joint stability during landing and are likely to contribute to the changes in landing technique that were evident during this time of rapid growth. The outcomes of this research provide a greater understanding of the lower limb musculoskeletal structural and functional changes throughout the adolescent growth spurt in girls, as well as the influence of these changes on landing technique in these pubescent girls.

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