Full Length ArticleMagnitude and variability of gait characteristics when walking on an irregular surface at different speeds
Introduction
Humans are exposed to uneven terrains in their everyday lives. These are either intentionally chosen, like during trail-walking, or unintentionally experienced, like facing cobbled sidewalks (Daley, 2008, Gates et al., 2012, Voloshina et al., 2013). Methods that induce gait instability on purpose, such as unstable footwear, have received increasing interest, as being regarded to provide general functional training benefits (Apps et al., 2017, Nigg et al., 2012, Romkes et al., 2006, Stöggl and Müller, 2012) or being used as rehabilitation tools (Landry et al., 2010, Waddington and Adams, 2004, Wedderkopp et al., 1991, Wester et al., 1996). These methods require the neuromuscular system to continually make alterations to counteract the instability induced, which has been observed through an increase in movement variability (Apps et al., 2017). Regular use of these methods is suggested to enhance balance and train lower-limb musculature (Nigg et al., 2012). Recently, irregular surfaces have been used to investigate the effects of less predictable and variable instability during locomotion (Sterzing et al., 2014, Müller and Blickhan, 2010, Voloshina et al., 2013).
When initially exposed to an irregular surface (IS), the infinite landing possibilities impair users’ ability to sense and control ground contact during walking, causing them to rely on active and passive lower-extremity alterations to maintain stability (Sterzing et al., 2014). Individuals demonstrated increased hip and knee joint flexion with lower ankle dorsiflexion during the gait cycle when walking on an irregular surface (Apps et al., 2017, Gates et al., 2012, Müller and Blickhan, 2010, Sterzing et al., 2014). Increased muscle activation of the gastrocnemius medialis (GM), vastus medialis (VM) (Apps et al., 2017, Voloshina et al., 2013), peroneus longus (PL) (Sterzing et al., 2014) and biceps femoris (Apps et al., 2017) are also acute responses. Further, increased variability in lower-limb kinematics and muscle activity is evident (Apps et al., 2017, Gates et al., 2012, Sterzing et al., 2014, Voloshina et al., 2013), which is associated with functional training benefits (Apps et al., 2017, Latash, 2012, Sterzing et al., 2014).
Locomotion speed is an important performance indicator which influences the biomechanical and physiological elements of movement. Alterations in gait speed influence metabolic cost (Moore et al., 2014, Russell et al., 2010), alter foot-strike patterns (Keller et al., 1996) and can cause the walk to run transition (Van Caekenberghe, Segers, De Smet, Aerts, & Clercq, 2010). It is widely documented that altering gait speed also influences the fundamental biomechanical characteristics of bipedal locomotion, such as spatio-temporal parameters, joint kinematics, kinetics, and muscle activity (Chiu and Wang, 2007, den Otter et al., 2004, Nymark et al., 2005, Schwartz et al., 2008, Van der Linden et al., 2002). Increasing gait speed is associated with reduced ground contact time, with individuals displaying increased hip and knee joint flexion during ground contact (Nymark et al., 2005, Schwartz et al., 2008, Van der Linden et al., 2002). Muscle activity of the GM, soleus, rectus femoris (RF) and biceps femoris (BF) increase with increasing walking speed during stance phase (den Otter et al., 2004). Gait variability has been found to reduce with increasing gait speed on regular surfaces (Almarwani et al., 2016, Dingwell et al., 2001, Dingwell and Marin, 2006, Li et al., 2005), where slower walking speeds pose a more challenging task to an individual’s motor control of gait (Hausdorff, 2004, Hausdorff, 2005). On irregular surfaces where instability is already present, reducing speed might further destabilise users, potentially enhancing the training stimulus. However, it is currently unknown if individuals respond similarly to speed changes when walking on regular and irregular surfaces.
When exploring how individuals initially respond to methods that induce gait instability, researchers often adopt self-selected speeds (Grimmer et al., 2010, Romkes et al., 2006, Wurdeman et al., 2012), whereby individuals will generally walk slower when exposed to unstable situations (Romkes et al., 2006, Wurdeman et al., 2012). This likely influences the magnitude of kinematic and muscle activity documented. As methods inducing instability are often used for training or rehabilitation purposes, understanding how walking speed influences the magnitude and variability of gait parameters in unstable situations is needed to ensure people are exposed to the right locomotion speed, to have them benefit the most from variable stimuli. Therefore, identifying how gait speed influences gait characteristics in an unstable condition is an important issue to address.
The purpose of this study is to determine initial changes in walking biomechanics on an unpredictable irregular surface, when walking speed is altered. This research is explorative in nature to determine if walking biomechanics alter similarly between regular surface and irregular surface walking when speed is altered. Based on previous research, it was hypothesised that walking on an irregular surface triggers postural adjustments, higher muscle activity and higher movement variability compared to walking on a regular surface, irrespective of gait speed.
Section snippets
Participants
Twenty physically active male sport science students (mean (SD): 22.2 (2.0) years; 1.80 (0.06) m; 67.1 (5.3) kg; 21.7 (1.8) kg/m2) participated in this research. Participants had no previous experience of instability training and had no lower extremity injuries in the previous six months. Ethical approval was granted from the corresponding University Human Research Ethics Committee and participants provided written informed consent.
Instrumentation
All walking trials were performed on a treadmill (Pro XL,
Results
No surface/speed interactions were reported across gait, kinematic or muscle activity parameters. Overall, gait, kinematic and muscle activity parameters varied similarly when walking on the RS and the IS, with increasing gait speed.
Discussion
This purpose of this study was to explore the effects of changing locomotion speed on walking biomechanics when walking on a regular and irregular surface. Altering gait speed was found to have a similar effect on walking biomechanics when walking on both surface conditions. Consistent with previous research, increasing gait speed was found to significantly increase ankle, knee and hip joint flexion (Nymark et al., 2005, Schwartz et al., 2008, Van der Linden et al., 2002) when walking on RS.
Conclusion
Walking on the irregular surface demonstrates similar responses to alterations in gait speed to walking on a regular surface. Increasing gait speed demonstrated higher hip, knee, ankle joint flexion and increased muscle activity when exposed to both the regular and irregular surface. The variability of gait, kinematic and muscle activity parameters was found to decrease with increasing gait speed, suggesting slower speeds pose a more challenging task to an individual’s motor control of gait.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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