Abstract
BACKGROUND:
Inclined walking is associated with multiple musculoskeletal benefits and is considered a therapeutic exercise. Various patterns of increased and decreased muscle activation with inclined surfaces have been observed in normal muscles, with more focus on the proximal lower limb musculature.
OBJECTIVE:
The aim of this study was to assess the differences in electromyographic activation of gastrocnemius, soleus, and tibialis anterior at various inclined surfaces during gait.
METHODS:
Fourteen healthy male participants aged between 17–30 years walked at a self-selected speed at motor driven treadmill on 0, 2 and 4 degrees of inclination. EMG activity of the muscles was recorded using the Delsys Trigno surface EMG system.
RESULTS:
Results showed that muscular activation of tibialis anterior significantly decreased with increase in the level of inclination (
CONCLUSION:
These differences in activation patterns found in distal extremity can be useful for designing rehabilitation protocols in sports training and for patients with neurological and musculoskeletal pathologies.
Introduction
Slow uphill walking is considered to be a moderate intensity exercise [1] and is associated with multiple benefits, including decreased joint loading [2], increased lower extremity joint range of motion and increased muscle activation [1], without any significant risk of damage [3]. For this reason, uphill walking has been suggested as a therapeutic exercise in addition to physical therapy for knee osteoarthritis [1, 3], musculoskeletal de-conditioning and even astronaut rehabilitation [4]. During uphill walking, increased muscular activation has been observed in gluteus maximus [5], gluteus medius [5], piriformis [5], quadriceps femoris [5, 6], hamstrings [5], peroneus [5], soleus [4, 5] and gastrocnemius [5, 6] muscles, with greater increase in proximal muscles as compared to distal muscles [7], and greater activation of soleus as compared to gastrocnemius [5]. On the other hand, decreased activation has been reported in gluteus minimus, iliopsoas and tibialis anterior muscles during uphill walking [5]. However, research has also shown conflicting results regarding the activation of muscles during uphill walking with patterns similar to that of level walking at smaller angles of inclination ranging from 5–10 degrees, and increased activation in gluteus maximus, hamstrings, vasti and soleus only at higher levels of inclination, from 15–20 degrees [8]. Then again, studies have shown lesser muscular activation during slow uphill walking as compared to brisk level walking [9]. In addition, research has also shown differences in muscle activation depending on gait patterns, for instance soleus muscle has been observed to have increased activation in rear-foot strike gait pattern and decreased activation in fore-foot strike pattern [4].
Furthermore, research has shown prolonged bed rest and de-conditioning to be associated with decrease in muscle force and volume, increase in fatigability and a shift to fast-twitch fiber type [4], with extensor muscles of the lower extremity being affected to a greater degree, such as soleus and gastrocnemius as compared to flexor muscles such as tibialis anterior [4, 10, 11]. Moreover, predominantly slow-twitch extensors such as soleus are observed to be more affected, in comparison to predominantly fast-twitch extensors such as gastrocnemius [4, 12]. Thus, it becomes very important to involve individuals into different types of physical activity and exercises to ameliorate the negative effects of muscle de-conditioning, with walking and jogging being the most commonly recommended activity or exercise. However, it is imperative to point out that level walking has been reported not to prevent muscle atrophy necessarily in debilitating conditions [4], and as previously mentioned soleus and gastrocnemius are affected more in response to de-conditioning in comparison to tibialis anterior [4, 10, 11], and a greater activation of soleus and gastrocnemius is observed during uphill walking [4, 5], signifying the importance and use of uphill walking in the rehabilitation process. Conversely, other studies have shown no significant increase in gastrocnemius activation with an increase in inclination or slope, except for very large angles of inclination [8]. Furthermore, even though meaningful changes do occur during uphill walking in the ankle muscles, most of the studies have focused on more proximal musculature [3].
Thus, in light of the existing findings, the purpose of the current study is to look into the differences in the activation of the distal lower extremity muscles during uphill walking at different angles and compare them with level walking, in order to provide important information that can be useful in the context of therapeutic exercise and rehabilitation training.
Materials and methods
Participants
Fourteen healthy young males aged between 17–30 years participated in the current study. All participants were selected on the basis of convenience sampling and were able to walk and run on inclined surfaces and level terrains. The included participants were free from any musculoskeletal injuries, physically active and had no recent history of physical trauma or burns. The participants signed an informed consent form after receiving detailed information on procedures and objectives of the study.
Design
EMG measurements were taken using Delsys Trigno wireless EMG system (Delsys Inc., Boston, MA, USA). The system has an integrated amplifier with four silver bar electrodes. It is very important to reduce artifacts during dynamic movements like gait, which is made possible with integrated electrodes of the EMG system. Ethical approval was obtained from the local ethical committee of National University of Sciences and Technology, Islamabad (approval no. ref#NUST/SMME-BME/REC/000129/20012019) and the data was recorded as per the ethical standards. The average accuracy of a Delsys sensor found in the literature is 95% [13]. Trigno EMG electrodes were unilaterally placed on the following muscles: tibialis anterior (TA), gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (S) according to SENIAM guidelines [14, 15] as shown in Fig. 1.
Electrode placement for gastrocnemius medialis, soleus, tibialis anterior and gastrocnemius lateralis. (a) Anterior view of distal leg, (b) posterior view of distal leg.
The electrodes were attached on the right leg of all the participants, therefore, total 4 channels were recorded on each participant. The evaluators included experienced physiotherapists and biomedical engineers with a knowledge of muscle anatomy and sensors handling. Double sided adhesive tape was used to attach the reusable electrodes directly to the participant’s skin. Priorto the experiment, participant’s skin was prepared and cleaned using isopropyl alcohol swabs. Subjects were asked to walk on a motor driven treadmill at a pre-set self-selected speed for 30 seconds at different inclination levels of 0, 2 and 4 degrees as shown in Fig. 2. Rest period of 30 seconds was given to each participant before the inclination level was changed. Recording was performed with the Delsys EMGworks software using 2000 Hz frequency for the EMG channels. Root mean square (RMS) value of maximum voluntary contraction (MVC) for each muscle was recorded which is an inbuilt system in the software. Reporting mean EMG values is considerably a better way for clinicians and researchers in terms of clinical relevance [16]. Therefore, mean RMS values have been calculated in the current study.
Different surface levels of treadmill, i.e. ground walking, 2 degrees of inclination, 4 degrees of inclination.
Muscular activation of three muscles of the distal lower limb, i.e. tibialis anterior, gastrocnemius (medialis and lateralis) and soleus measured in micro volts, were the dependent variables of the study whereas different surface levels, i.e. level walking, inclination level 2 and inclination level 4, were the independent variables of the study. The data was not normally distributed (
Demographic characteristics of the participants
Demographic characteristics of the participants
EMG values of muscles at different surface levels in terms of median and interquartile range
A total of 14 male participants were included in the study. Their mean age, weight, height, and body mass index (BMI) are shown in Table 1. Tibialis anterior, soleus, gastrocnemius medialis and gastrocnemius lateralis muscular activation was reported in the form of median (IQR) as shown in Table 2.
EMG activation of tibialis anterior was found to decrease with the increase in inclination level and statistically significant difference was observed between the EMG scores of three surface levels with p-value of less than 0.05 (Table 2). However, in terms of soleus, gastrocnemius medialis and gastrocnemius lateralis muscular activation patterns, there was no statistically significant difference (
Discussion
The current study aimed to assess the differences in the activation of soleus, gastrocnemius, and tibialis anterior muscles by increasing the level of surface inclination. The results of the study showed that the activation of tibialis anterior muscle significantly decreased with increase in the level of inclination. However, no significant difference in muscular activation was found in gastrocnemius medialis, gastrocnemius lateralis and soleus muscles of the participants when the level of inclination was increased and also between the muscles at different levels.
Difference between muscle activation of tibialis anterior, soleus, gastrocnemius lateralis, and gastrocnemius medialis at ground level, inclined level 2, and inclined level 4.
values less than 0.05 shows no statistically significant difference between all the muscles at three levels
Difference between muscle activation of tibialis anterior, soleus, gastrocnemius lateralis, and gastrocnemius medialis at ground level, inclined level 2, and inclined level 4.
Mean root mean square (RMS) values of tibialis anterior at ground level, 2 degrees of inclination and 4 degrees of inclination. The figure shows that increasing the level of inclination decreases the mean RMS values.
Opinions about the reported EMG muscular activation of the lower limb muscles by altering the surface inclination levels is inconsistent in the existing limited evidence. However, the findings of the current study related to tibialis anterior are in accordance with the study conducted by Alexander et al. [17]. The researchers in this study analyzed the effects of inclined walking on lower limb muscle forces. Force plates were used to determine the kinetic data of the lower limb muscles. It was found that the force produced by tibialis anterior during walking significantly decreased (
Evidence suggests that muscular activation of gastrocnemius and soleus increases with increase in the level of inclination. This pattern was studied in detail by Ohira et al. [4]. According to the results of the study, the EMG activity of soleus muscle was found to be increased with increase in the level of inclination. This was specifically found in individuals who stepped down using heel (heel strikers or rear-foot strikers). However, the participants who stepped down using toes (toe strikers or fore-foot strikers), the EMG activity of soleus was found to decrease with increase in the level of inclination whereas the activation of gastrocnemius was increased. Foot-strike patterns effects the muscular activation and must be considered before analyzing the muscular activation patterns of individual muscles. In the current study however, the importance of foot-strike pattern was known post data recording process. Therefore, in future studies, it is suggested that the foot-strike patterns must be considered along with EMG activation of the lower limb muscles for analyzing the accurate muscular activation patterns and for optimum walking exercise prescription.
One of the reasons of insignificant results between the distal musculature at different levels is that the muscles of distal lower extremity are tightly controlled compared to the proximal musculature. This has been discussed in the study conducted by Patela. The results of this study showed that muscle activation in proximal muscles of the leg was greater than tibialis anterior, soleus and gastrocnemius. Furthermore, the muscular activation with the percentage increase in incline level increased between all the muscles which in contrast to the results of the current study [7].
The gait training of the individuals suffering from neurological and musculoskeletal pathologies is very necessary for their optimum functioning [18]. This study can be very beneficial for training of the individuals with pathologies affecting gait. For example, a patient has a weak tibialis anterior and a physical therapist/rehabilitation professional want to strengthen that muscle through inclined walking, with a doubt of risk of injury. The results of this study provide the fact that increasing the incline level would not cause injury to the muscle (Because increasing the inclination decreases tibialis anterior muscle activation).
The limitations of the current study include lack of advanced treadmills (due to lack of resources at the study setting) and unavailability of participants due to the pandemic. Furthermore, inaccessibility to the technology, e.g. 3D gait analysis, further eliminated number of variables which would otherwise be studied in detail.
From a biomechanical perspective, it is recommended that along with the consideration of foot strike patterns, consideration of intrinsic foot muscle activity [19], muscle activation in relation to the phases of gait and walking step rate [20, 21] should also be included as future variables to have a better insight in the variation of muscle activation in distal extremity.
The current study provides details on the activation patterns of gastrocnemius, soleus, and tibialis anterior at inclined levels that can be beneficial for developing rehabilitation training protocols where the aim is to activate specific muscles at a particular level. Furthermore, comparison of the data taken from healthy population to non-healthy individuals in future will give an insight on training of the specific muscles on inclined levels.
Footnotes
Acknowledgments
The authors would like to acknowledge 502 workshop, Rawalpindi Pakistan for their technical support and for the provision of treadmills used for conducting the research.
Conflict of interest
The authors declare no conflict of interest.
Funding
This research received no external funding.