Quadriceps strength asymmetry in transtibial amputees and able-bodied

: mechanisms and association with movement

Abstract

Bilateral strength asymmetry of the quadriceps muscles has been implicated in a variety of special populations and movement performance deficits. However, while there is consensus of the main determinants of maximal and explosive strength, it is unclear to what extent these may determine strength asymmetries. The association between asymmetries in quadriceps strength and movement are also not well understood. This thesis aimed to determine the magnitude and variability of quadriceps maximum and explosive strength asymmetry, the underpinning neuromuscular determinants of these asymmetries, and the association of these asymmetries with movement. These aims were investigated in two populations distinct in their degree of habitual movement asymmetry during typical lower-body activities; able-bodied and individuals with unilateral transtibial amputations (ITTAs). This thesis also aimed to assess the effects of long-term muscle disuse, caused by habitual asymmetrical loading during movement in the ITTAs. The magnitudes of maximum and explosive strength asymmetry were similar (10% and 13%, respectively) in able bodied, and not explained by any systematic combinations of asymmetries in the neuromuscular determinants of strength (e.g. neural activation, muscle architecture and contractile properties). In both able bodied and ITTAs there was a greater variability in explosive strength asymmetry compared to that in maximum strength, which was associated with loading asymmetry in drop landings in able-bodied, and a good predictor of walking speed in ITTAs (r = -0.83). Additionally, greater strength asymmetry in ITTAs was associated with greater asymmetry in single support time (r = 0.60 – 0.83) and limb loading asymmetry (r = 0.54 – 0.89) at faster walking speeds. When utilising ITTAs as a model for long-term muscle disuse, we found substantially greater strength decrements than could be predicted from short-term disuse studies in otherwise young, healthy, and active adults. The reductions in maximum voluntary torque (MVT; -59%) were likely due to considerable declines in muscle thickness (-41%) and neural drive (~-44%), whilst reductions in explosive strength (-75%) appeared due to the decline in MVT, coupled with a slowing of the contractile properties. Overall, the results from this thesis suggest that asymmetries in explosive strength play a more important role in movement in both populations than maximum strength asymmetry. Furthermore, the novel findings from this thesis may help to inform the development of intervention programmes to target strength asymmetry in ITTA populations, and additionally, to combat the degenerative changes present in muscle as a by-product of long-term disuse.

Date of Award	10 Dec 2019
Original language	English
Awarding Institution	University of Roehampton
Supervisor	Siobhan Strike (Supervisor) & Neale Tillin (Supervisor)