Browsing by Subject "Quadriceps"

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Differential activation of the vastus medialis and the vastus medialis oblique in individuals with and without patellofemoral pain syndrome
(2019-06-18) Peng, Yi-Ling; Griffin, Lisa
An imbalance of medial and lateral quadriceps control can lead to patellofemoral pain syndrome (PFPS). The incidence rate of PFPS is twice as high in females than in males. The aims of this research were to investigate sex differences in quadriceps neuromuscular control and motor unit recruitment properties in healthy individuals comparing to those with PFPS. We also investigated optimal leg position and levels of force production to target the vastus medialis oblique (VMO). In Study One, quadriceps surface EMG onset time and amplitude were examined at different submaximal force levels in asymptomatic males and females with and without PFPS. Females showed a 320 ± 70 ms delay in average quadriceps onset time relative to males. The vastus lateralis (VL) and VMO activated together and prior to the vastus medialis (VM) and rectus femoris. A low force (25%MVC) generated the lower VMO:VL ratio compared to 50% and 75% MVC. In order to determine if the VMO was controlled independently of the VM, Study Two examined motor unit recruitment patterns in the VM and VMO in healthy males and females when performing straight leg tasks in two different hip positions. VMO motor units were recruited 2.92 ± 1.28% MVC earlier than VM motor units. Females fired motor units in the vastus medialis complex faster than the males. We found that hip position is a crucial factor influencing motor unit recruitment properties in the vastus medialis complex. In a neutral hip position, motor units in the VM were activated at lower recruitment thresholds and at faster firing rates compared to in lateral hip rotation. Study Three evaluated the effect of PFPS on VM and VMO motor unit recruitment during two different hip positions of straight leg raise in females with and without PFPS. Individuals with PFPS showed an altered control strategy of VMO motor units between the two hip positions compared to healthy individuals. A traditional straight leg raise without hip rotation generated greater VMO motor unit initial firing rates in healthy individuals. However, VMO motor units were recruited at faster rates in lateral hip rotation for individuals with PFPS. The findings from this series of studies indicate that the neuromuscular control strategies of the quadriceps muscle subsections were affected by sex, PFPS, hip position as well as force level. These factors should be taken into consideration when designing rehabilitation protocols.
Sex differences in quadriceps alternating muscle activation patterns during fatigue
(2021-07-30) Morrison, Drew Terris; Griffin, Lisa
Synergistic alternating muscle activation (AMA) consists of a period of co-activation (Co-A) and a period of trade-off (TO). Together they form a load-sharing cycle which is a neuromuscular control strategy that attenuates fatigue. However, the structure of AMA interactions of synergistic muscles has only been investigated during low-level contractions of 2.5-10% maximal voluntary contraction (MVC) and has yet to be investigated at moderate force levels (≥ 20% of MVC) and differentiated between the sexes. The purpose of this study was to quantify the activation relationship between pairs of synergistic quadriceps muscles to further understand the patterns (durations of Co-A and TO and frequency of AMA cycles). Surface electromyographic (EMG) data was collected from 16 individuals (8 male, 8 female) from the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), and vastus medialis oblique (VMO) during a fatiguing contraction at 20% MVC. Synergistic muscle pairs (VL-RF, VL-VM, VL-VMO, RF-VM, RF-VMO, VM-VMO) were analyzed for Co-A, TO, and AMA frequency during 3 phases of the fatiguing contraction. The synergistic pairs were in Co-A significantly longer than TO during all fatigue phases. Some muscle pairs differed significantly from each other in time spent in each state (Co-A or TO) during the final contraction phase. There was no significant difference in AMA patterns within individual muscle pairs between fatigue phases. There were strong positive and negative correlations between endurance time and Co-A and TO durations respectively for every muscle pair in males during the final two fatigue phases. For the same measures in females, only the RF-VL, RF-VMO, and VL-VM muscle pairs demonstrated a significant negative and positive correlation in the middle fatigue phase for Co-A and TO respectively. AMA was present in both male and female EMG data, but contrary to expectations that AMA cycle frequency would produce significant differences throughout the contraction, the endurance time correlations were where significant differences were present.