Stroke usually results in hemiparesis or muscle weakness contralateral to the cerebral lesion, increased abnormal muscle tone, and deficit of coordination (Geyh et al., 2004). Muscle impairments on the paretic side are associated with limitations in activities of daily living (ADL), such as walking (Nasciutti-Prudente et al., 2009) and sit-to-stand (STS) (Bohannon, 2007). Asymmetric dynamic posture and movement is the most prevalent locomotor deficit associated with stroke-related hemiparesis (Winstein et al., 1989). Weight-bearing asymmetry has been linked to impaired motor function and the standing balance problems of stroke patients (Pyöriä et al., 2004). Impaired motor function may be a result of muscle weakness or abnormal tone causing difficulty in muscle use and leading to increased postural sway, thus leading to an increased risk of falling (Chitra and Mishra, 2014).

The STS task is considered a necessary condition for upright movement and for performing other important daily activities such as locomotion (Bohannon et al., 2008). Thus, STS performance is fundamental for independence (Janssen et al., 2010). The quadriceps considered a primary motor muscle of the STS task because it promotes knee extension and contributes to hip flexion and stability (Khemlani et al., 1999). The tibialis anterior (TA) is important during the initial phases of the STS to stabilize the foot on the ground, the soleus seems to have an important function in postural adjustments at the end of the STS (Lomaglio and Eng, 2005). Electromyography (EMG) activity of the quadriceps, TA, and soleus muscles in the less affected lower limb was higher than that in affected lower limb during STS task in stroke patients (Prudente et al., 2013). Stroke patients exhibit asymmetrical weight bearing during the STS, placing approximately 41.5% less load on the paretic leg, and this asymmetric pattern affects gait performance (Chou et al., 2003). After stroke, many people have difficulty standing up and walking independently, due to motor impairments such as weakness and poor coordination (de Sousa et al., 2019).

Walking dysfunction is a major problem for many people afflicted by stroke (Algurén et al., 2010). Functional gait is an important factor in ADL (Tomoyuki and Shigeru, 2010). The ability to walk is determined by several factors, including balance, motor function, and endurance, and is affecting by impairments in muscle strength, sensory function, and other factors (van de Port et al., 2008). The slow walking speeds commonly observed following stroke are associated with marked temporal and spatial interlimb asymmetries (Patterson et al., 2010). A major characteristic of hemiplegic gait observed in stroke patients is walking asymmetry, which may increase the risk of falls (Yen et al., 2015). Spatiotemporal gait asymmetry was correlated with muscle weakness (Hsu et al., 2003).

Therapists are aware of the importance of STS and walking after stroke, and the relationship between STS ability and walking performance has been investigated in several studies. However, studies on the relationship between STS asymmetry and gait asymmetry are lacking. Therefore, in this study, investigated the relationship between both lower limb muscle asymmetry during STS and spatiotemporal gait asymmetry in subjects who had a stroke.

STS control is closely related to ambulatory ability. After a stroke, the brain’s ability to perform the STS becomes asymmetric because of weakness on the affected side and the loss of postural control (Chou et al., 2003). The peak power level required for one to rise from a chair may be related to leg muscle strength and the ability to walk (Cheng et al., 1998). The present study has investigated the relationships between lower limb muscle asymmetry during STS and spatiotemporal gait symmetry in stroke patients. The results of present study found significant correlations between both lower limb muscle asymmetry during STS and spatiotemporal gait asymmetry.

The results of the present study showed positive correlation between GCM and RF asymmetry during STS and step length asymmetry during gait. Quadriceps muscle weakness may be related to loading asymmetry during the STS task (Christiansen et al., 2013), and ankle plantar flexor strength contributes the most to STS performance (McCarthy et al., 2004). Prudente et al. (2013) reported that the significant compensations occur on the nonparetic side instead of the paretic limb during STS task. Lower limb muscle strength and weight-bearing symmetry are related to STS in stroke patients (Lomaglio and Eng, 2005). The results of the present study found that GCM and RF activity are asymmetrical during STS. Although this study measured only part (RF) of the quadriceps and part (GCM) of the plantar flexor, the results are the same as in the previous study. Ankle plantar flexor function is mainly active in the single-leg stance phase during gait (Lamontagne et al., 2002). Allen et al. (2011) reported that patients with poststroke hemiparesis show a common impairment in the ankle plantar flexion moment impulse, but that different compensation mechanisms are utilized by patients according to the pattern of step length asymmetry. In a previous study, patients with a maximal vertical force difference of less than 30% of the patient’s body weight between their legs during STS had better gait performance than other stroke patients (Chou et al., 2003). Considering the present study’s results, it seems that the asymmetry of RF and GCM muscle activity during STS affects the step length asymmetry during walking in stroke patients.

The results of the present study showed positive correlation between RF asymmetry during STS and step time asymmetry during gait. Development of ipsilateral quadriceps weakness after stroke is associated with delayed recovery of function (Harris et al., 2001). Quadriceps weakness can decrease shock absorption capacity during walking, leading to accentuated symptoms and changes in gait patterns to maintain functionality (Clermont and Barden, 2016). Spinoso et al. (2018) reported that knee extensor strength is correlated with step time, and suggested that muscle weakness results in temporal changes in gait. Considering the present study’s results, it seems that the asymmetry of RF muscle activity during STS affects the step time asymmetry during walking in stroke patients. This finding corresponds to those of previous study (Park et al., 2016) that the observed that gait pattern changes are associated with weakness of the anterior thigh muscles.

The results of the present study showed that FTSTS times were significantly negatively correlated with gait speed. The FTSTS times correlated with functional muscle strength of the lower limbs and dynamic standing balance of stroke patients (Ng, 2010). Stroke patients who take less time to rise from sitting show significantly better gait velocity, cadence, and stride time (Chou et al., 2003). In addition, Chan et al. (2017) reported that FTSTS times are significantly correlated with Timed Up and Go test motor times. The result of present study found that a shorter FTSTS time is correlated with increased gait speed, consistent with previous findings.

The present study had some limitations. First, the sample size in this study was small. Second, we examined only a few lower limb muscles. Third, this study did not record kinetic data such as ground reaction force throughout the experiment. Future studies should include more muscle groups and collect kinetic data.

This study found a positive correlation between GCM and RF asymmetry during STS and step length, step time asymmetry during gait. FTSTS times were significantly negatively correlated with gait speed. Therefore, to improve step length and step time symmetry, it is necessary to apply exercises that focus on GCM and RF symmetry during STS. In addition, to improve gait speed, it is necessary to apply exercise that focuses on increase STS speed.