Muscle imbalance among elite Australian rules football players: a longitudinal study of changes in trunk muscle size.
BACKGROUND
Trunk muscles, such as the transversus abdominis (TrA) and multifidus, play a key role in lumbopelvic stability, which is important in athletic performance. Asymmetry or imbalance in these and other trunk muscles could result from the specific requirements of  the game of Australian rules football.


OBJECTIVE
To determine whether seasonal variations in the sizes of key trunk muscles associated with lumbopelvic stability occur in Australian Football League players.


METHODS
Cross-sectional study.


METHODS
Hospital.


METHODS
The number of players eligible to participate at each of the 4 time points was 36 at the start of preseason 1 (T1), 31 at end of season 1 (T2), 43 at the end of preseason 2 (T3), and 41 at the start of preseason 3 (T4). The group with  data at all 4 time points (n = 20) was used in the analyses and was shown to be representative of the total sample.


METHODS
Magnetic resonance imaging was used to determine the cross-sectional areas (CSAs) of the multifidus (vertebral levels L2 to L5) and lumbar erector  spinae (LES) muscles (L3), as well as the thickness of the TrA and internal oblique (IO) muscles at L3.


METHODS
Cross-sectional areas of the multifidus and LES muscles and thickness of the TrA and IO muscles.


RESULTS
By the end of the playing  season, results showed 11.1% atrophy for multifidus CSA at L3 and 21% atrophy for TrA thickness at rest. In comparison, the CSA of the LES muscles increased by 3.6%, and the thickness of the IO muscle increased by 11.8% compared with the start of the preseason.


CONCLUSIONS
The results indicated an imbalance of the key muscles associated with lumbopelvic stability.
School of Physiotherapy, Australian Catholic University, Banyo, Queensland 4014, Australia. julie.hides@acu.edu.au
Julie
J
Hides
Warren
W
Stanton
D000009:Abdominal Muscles / Q000502:physiology*; D056352:Athletes; D001315:Australia; D003430:Cross-Sectional Studies; D005538:Football; D006801:Humans; D008137:Longitudinal Studies; D008161:Lumbosacral Region; D008279:Magnetic Resonance Imaging; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D012621:Seasons