Date of Award

Summer 8-17-2015

Degree Type


Degree Name

PhD Health Sciences


Health and Medical Sciences


Doreen Stiskal, Ph.D.

Committee Member

Lee Cabell, Ed.D.

Committee Member

Genevieve Pinto Zipp, Ed.D.


gait initiation, balance, muscle activation, speed, middle-aged adults


Middle-age adults’ (MA) self-report of falls are greater compared to younger adults (YA) during ambulation. A previous study found that MA compared to YA use different strategies taking one-step forward at a fast speed. No other studies have compared the effect of two different speeds on balance variables and muscle activity during gait initiation in the MA compared to YA using an instrumented walkway. The objectives of this study were to assess the effects of age and speed on balance by measuring a) the Center of Pressure (COP) in two planes: COPx (sagittal) and COPy (frontal) and the Center of Mass-Center of Pressure (COM-COP) distances, and b) activation of lower extremity muscles (onset/offset, average amplitudes) during gait initiation. Thirteen healthy MA (Mage = 54.0 years, age range: 52-61 years) and nine healthy YA (Mage = 25.5 years, age range: 19-35 years) had surface electromyography (EMG) signals of the gluteus medius (GM), adductors (ADD), tibialis anterior (TA) and medial gastrocnemius (MG) recorded while initiating three steps forward while walking on a GAITRite® platinum mat at a normal self-selected and fast walking speed for 10 trials each. COP and COM-COP distances were measured using ProtoKinectics Movement Analysis Software-PKMAS. Rectified surface EMG signals were normalized using Maximum Voluntary Contractions (MVCs). Post hoc analysis used a Two-Way Mixed Design ANOVA. TA on the swing leg shuts off significantly later in the MA when compared to YA when taking a faster step (p = .04). MG on the stance leg activates significantly earlier in the MA when compared to YA when taking a faster step (p = .04). Middle-age adults activate the MG earlier in response to the greater amount of COM displacement at a faster speed. As a result the efficiency of the TA activation, which is used to generate velocity, is compromised in order to maintain balance. The changes in timing in the MA may be precursors to age-related spatial and temporal changes. This study highlights the impact of speed on initiating gait and the importance of incorporating it into the evaluation of MA.