Changes in the Trend of Walking Motor Control in Athletes with Anterior Cruciate Ligament Deficiency in Response to Progressive Perturbation Trainings

  

    

    
SI*
    
M-A*
    
M-nA*
    
VRI-A*
    
VRI-nA*
  
  

    
Perturbation group
    
Pre-test
    
M 
    
    0.45
    
    10.29
    
    13.21
    
    4.55
    
    5.46
  
  

    
SD 
    
    0.15
    
    2.11
    
    5.75
    
    1.64
    
    2.11
  
  

    
Post-test 
    
M 
    
    0.58
    
    28.53
    
    30.67
    
    18.55
    
    19.24
  
  

    
SD 
    
    0.18
    
    14
    
    14.14
    
    14.18
    
    14.77
  
  

    
P-value intra-group 
    
    0.08
    
*0.000
    
    *0.000
    
    *0.003
    
    *0.002
  
  

    
ES Cohen’s d 
    
    0.81
    
1.89
    
    1.67
    
    1.43
    
    1.35
  
  

    
Standard group 
    
Pre-test
    
M 
    
    0.48
    
    9.59
    
    16.11
    
    4.9
    
    7.74
  
  

    
SD 
    
    0.18
    
3.7
    
    4.78
    
    2.78
    
    3.51
  
  

    
Post-test 
    
M 
    
    0.42
    
    12.17
    
    12.7
    
    5.14
    
    5.13
  
  

    
SD 
    
    0.19
    
4.13
    
    4.61
    
    2.81
    
    2.53
  
  

    
P-value intra-group 
    
    0.39
    
0.17
    
    *0.02
    
    0.85
    
    *0.05
  
  

    
ES Cohen’s d 
    
    0.39
    
0.68
    
    0.75
    
    0.09
    
    0.89
  
  

    
Inter Group differences 
    
P-value
    
Pre-test
    
0.52
    
0.53
    
    0.14
    
    0.68
    
    *0.04
  
  

    
Post-test 
    
    *0.03
    
*0.000
    
    *0.000
    
    *0.001
    
    *0.001
  
  

    
ES Cohen’s d 
    
    0.89
    
1.64
    
    1.77
    
    1.36
    
    1.38
  
  

    
SI*:    Similarity Index; M-A*: Magnitude of Affected Limb; M-nA*:    Magnitude of non-Affected Limb; VRI-A*: Voluntary Response Index    Affected Limb, VRI-nA*: Voluntary Response Index Non-Affected    Limb; M: Mean; SD: Standard Deviation.
  

Table 6: Intra-group and inter-group comparison of sEMG variables in walking test.

In the intra-group comparison, the perturbation group in the post-test showed a significant improvement with a huge effect of ES in the VRI variables in both legs.

Discussion

Suitable individuals to participate in this study were copers who were selected by the protocols of previous studies [2,14,15]. In the results of statistical analysis on walking task sEMG variables, the two groups of perturbation and standard were homogeneous in the pretest comparison and did not differ from each other. However, after therapeutic training interventions, significant differences were found between two groups in SI and VRI in both legs, so that in inter-group comparisons perturbation training in all variables founded large to huge effects in both legs. According to the findings of the present study, the amount of SI in the walking task increased in the perturbation group and the VRI of the injured limb was extended to the PRV of the healthy limb. sEMG patterns increased after intervention in both limbs of the perturbation group, and symmetry was obtained between the two limbs in the walking task. However, in the post-test of the standard group, although the VRI of the injured limb was extended to the PRV of the healthy limb of the same group, the SI in this group showed a small decrease in ES due to a decrease in muscle activity in the healthy limb and an increase in moderate activity of muscles in the injured limbs. As a result, in the perturbation group, the increase in muscle activity in both limbs was associated with an increase in SI, but in the standard group, a small decrease in muscle activity in a healthy limb and a small effect in muscle activity in an injured limb was associated with a decrease in SI. Thus, although symmetry between the two limbs was obtained in the post-test of both groups, the muscle activity in the walking task in the perturbation group was significantly higher than the standard group.

According to studies, few studies have been conducted in the field of walking activity in ACLD individuals and the calculation of overall muscle activity, and most studies have examined the kinetic and kinematic components in more details. Preliminary studies of perturbation trainings performed on ACLD individuals with the goal of returning to high levels of exercise without surgery by Fitzgerald et al. showed that athletes in 93% of cases reporting no successful GW professionally returned to sport while only 50% of participants in standard training protocols were able to return to previous activity levels [11,14]. So, the documented non-surgical treatment algorithm for ACLD individuals is enhanced perturbation rehabilitation [4,5]. Because by doing perturbation training, the afferent pathways that provide information to the muscle spindles are stimulated, and as a result, joint stability is improved by increasing the activity of gammamotor neurons and increasing the sensitivity and readiness of the muscle spindles in response to disruptive forces [3,12,14].

Researchers have shown in previous studies that perturbation training, compared with strength training alone, causes limb symmetry in walking and increases quadriceps strength in both limbs, which is also present in the six-month follow-up after surgery [3]. Studies have also shown that perturbation training improves the gait patterns of potential copers by creating dynamic stability in the knee [1,3-5], and improves the gait deviations in non- copers(3), these results were similar to the results obtained in our study in the form of an increase in the SI of the two limbs in the perturbation group.

Yim et al. showed that ACLD knees in the stance phase of walking shift the tibia more anteriorly with less extension in the sagittal plane [6], and people with ACLD may position their knee into more external rotation to prevent excessive motion into internal rotation in the frontal plane [6,10]. In this study, individuals adopt their gait biomechanics to avoid these anterior and rotational instabilities in turning maneuvers, and reduced the range of motion of ACLD knee by freezing movements in the horizontal plane during the stance phase as an adaptive reaction to prevent further knee vulnerability [6]. In contrast some studies did not exhibited any gait deviations in ACLD knees on the sagittal plane compared with controls [10]. In addition, some studies have shown that ACLD individuals have an increase in the activity of the knee flexors in the stance phase of walking to prevent the tibia from moving forward, causing degenerative shear forces in the knee joint [1,6,23], and adopted a changed gait pattern called quadriceps avoidance associated with decreased quadriceps contraction [8].

With progressive perturbation training, symmetry of both limbs and stability of the knee increased with increasing co-contraction index and the decrease of flexion in the knee joint in the stance phase of gait and the ACLD limb becomes similar to healthy individuals and is a positive adaptation to increase knee joint stability [1,5]. Increased co-contraction is a positive factor and means dynamic stiffness of the knee, which occurs during the functional activities of the normal mechanics of the knee and is associated with a decrease in torque and movement of the knee [1]. In contrast, Chmielewski et al. showed that perturbation training with neuromuscular changes caused the reduction of co-contraction in the muscles around the knee, and in the post-test walking task, knee flexion angles increased in order to adapt to unpredictable surfaces, which was in contrast to the results of other studies that believed that co-contraction would also increase [11].

Another important approach in ACLD individuals is quadriceps muscle strength deficiency [3-5,8], which is one of the main causes of osteoarthritis of the knee and gait disorders and functional defects [1,3]. When the symmetry of the two limbs increases, the injured limb can resist high-risk physical activity and the risk of osteoarthritis is reduced [4]. It has also been reported that by performing perturbation training, in addition to improving neuromuscular control, an increase in strength is observed, especially in the quadriceps muscle [4,11].

In our study, the kinematic components of gait activity were not examined, however, the results of the study showed that mechanical perturbation training increased the overall stability of the knee joint and increased the symmetry between the two limbs by increasing the overall muscle activity. Perhaps the symmetry created in the walking task can be defined as a kind of muscle co-contraction, and the overall increase in muscle activity in the walking task can be considered as an increase in strength and stability in the knee joint. However, due to the lack of information on co-contractile gait in ACLD individuals, judgment is difficult and requires further study.

In several studies, the effects of manual and mechanical perturbation training have been investigated, and all of these studies have confirmed the long-term effectiveness of perturbation trainings [1,3-5,7,11,12,14,15]. The use of manual perturbation training in clinics is done one by one and depends on the presence of a therapist and spending a lot of time for treatment is mandatory. In addition, because these types of manual perturbation training can only be performed on limited motion axes and cannot simulate normal functional movements such as jumping and changing directions, researchers have always been looking for more appropriate mechanical perturbation training substituting manual types in the literature. Usually, these manual types of training are not used or are rarely used in clinics due to their difficult use. On the other hand, mechanical perturbation rehabilitation programs, which are controlled and progressive perturbations, are now included in rehabilitation programs and have better results than manual perturbation trainings [1,4,5]. therefore, in comparative studies between manual and mechanical perturbation trainings, the researchers showed that Both perturbation training modes improved the patients’ self-reported of knee functional performance and helped walking with more knee flexion excursion and moment [7]. On the other hand, by performing mechanical perturbation training compared to manual perturbation, gait symmetry is improved in individuals and knee stability is increased by reducing flexion in the knee joint in the stance phase in the ACLD limb similar to healthy individuals [5], and also increasing co-contraction in larger muscles and more muscular forces are produced during walking [1], although it has been pointed out that the benefits of this stability are not clear.

In our study, only the perturbation mechanical machine was used and we did not have a manual perturbation training group to compare. However, the results of our study showed that mechanical perturbation training increases the stability of the knee joint by increasing the distribution of overall muscle activity. The results obtained in this study, in line with previous studies [1], suggest that perturbation training on mechanical plates with the production of greater muscle force while walking can be effective in transferring to other more complex motor activities. Also, one of the advantages of unpredictable mechanical training is achieving dynamic knee stability and functional knee function in less time and less labor force [4,7].

Compared to previous studies, with the present study, it can be said that none of the devices that created mechanical perturbation included all the axes of motion and were often limited to one or two axes of motion. In the present study, however, a device was used that produced unpredictable perturbations in all motion axes that had not been studied in previous studies. However, the perturbation instrument in this study has newer capabilities that can be performed both in the closed movement chain of functional exercises and is effective on all joints of the trunk and lower limbs, as well as rapid motor reactions to provides compensation in maintaining the center of mass at the base of support to maintain balance. Also, studies suggest that it is better to use perturbation tools in training that are both mechanical and not habitual, because habitual phenomena reduce muscle strength. It is thought that by the use of this perturbation training device, the adaptation that typically occurs in the first and second attempts at the use of steady manual and mechanical perturbations [24], does not occur and this requires further study.

Also, in a review of questionnaire studies and functional tests, researchers have shown that ACLD individuals undergoing perturbation treatments show improved limb symmetry in functional activity and improved knee function [4], and these findings were in line with the results of our study. Although the two training groups were not homogeneous in the pre-test questionnaire studies, and the standard group had a higher quality questionnaire, but in the post-test comparison of the perturbation training group, there was a moderate increase achieved in the sports and recreation section of the KOS-ADLS questionnaire and a small increase in the IKDC 2000 questionnaire. This means that perturbation trainings were much better than standard trainings in improving a person’s mental health to reach previous levels of exercise, and these results were consistent with the results of functional tests in our study.

Moreover, in the evaluation of functional tests, the perturbation group in the ACLD limb showed significant improvement even though no significant improvement was seen in the standard group (Figure 2). These results show that perturbation trainings are preferable to strength, endurance, neuromuscular, balance and agility exercises alone, and perhaps one of the reasons is the presence of cognitive characteristics in this type of exercise and this requires further studies. According to research by Zhang et al. when perturbations are not visually predictable, strong predictive activity occurs and latencies in the tested muscles become shorter, meaning that unexpected postural perturbations with increase in cognition load improves body stability after perturbation [25].

    

    

    Figure 2: Changes in the VRI in response to walking task in perturbation
training group and standard group of both ACLD and healthy limbs. The
direction of the arrows shows the trend of changes from the beginning to the
end of the sEMG tests. Continuous lines indicate the perturbation training
group and dotted lines represent the standard training group. A solid arrow
indicates a healthy limb and a hollow arrow indicates an ACLD limb. In the
plot, the ACLD limb in the perturbation group is drawn towards the healthy
limb response pattern, and both limbs show a similar increase in the size of
the response vector. However, the plot clearly shows a negatively decrease in
the magnitude of response vector of the ACLD limb towards the healthy limb
in the standard group.