The effect of stop X exercises on balance, strength and range of motion of football players with dynamic knee valgus defect

doi:10.21203/rs.3.rs-4875904/v1

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The effect of stop X exercises on balance, strength and range of motion of football players with dynamic knee valgus defect

https://doi.org/10.21203/rs.3.rs-4875904/v1

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Dynamic valgus of the lower limb is known as a risk factor associated with improper muscle function for many lower limb injuries, especially knee injuries. Therefore, the aim of the present study was to investigate the effect of Stop X exercises on the balance, strength and range of motion (ROM) of football players with dynamic knee valgus (DKV) defect. Thirty football players with dynamic knee valgus defect were selected purposefully and were randomly divided into two groups, control (n = 15) and training (n = 15). Stork tests, Y-balance test (YBT), goniometer, and digital dynamometer were used to evaluate static balance, dynamic balance, ROM, and hip abduction and external rotation strength, respectively. Analysis of covariance and dependent t-tests were used to compare the between and within group differences. There is a significant difference between the groups in the variables of hip abduction and external rotation strength and ROM, static balance and total score of YBT. The results demonstrated that performing Stop X exercises resulted in significant improvements strength and ROM of the hip, static and dynamic balance of football players with DKV defect, which show the importance of using these exercises to improve balance, muscle strength and ROM in this group of football players.

Health sciences/Health care

Health sciences/Anatomy/Musculoskeletal system

dynamic knee valgus defect

balance

range of motion

strength

stop x exercises

Football is one of the most popular sports in Iran and the world, which is inherently traumatic, and anterior cruciate ligament (ACL) injury is one of the most common injuries in this sport field.¹ This injury is more common in young amateur football players than in adult ones.² Regarding injury in adolescents, in a 10-year survey from 2005 to 2015 and in the age range of 5 to 14 years, a total of 320 ACL injuries were reported, the highest amount of which (96.9%) was in the age range of 10 to 14 years and sports activities accounted for 56.6% of ACL injuries.³ It is reported that 70% of ACL injuries are non-contact and 30% are contact-type.^4,5 It has been reported in Iran that 46% of all knee injuries in football and volleyball are attributed to ACL.⁶ Four neuromuscular defects including trunk dominance, ligament dominance, quadriceps dominance, and leg dominance have been introduced as underlying mechanisms of ACL injury,⁷ which can be used to screen and determine individuals with inappropriate movement patterns and prone to ACL injury.⁸

Valgus defect (ligament dominance) is one of the most common neuromuscular defects that is triggered when the necessary dynamic stability is not provided for the joint by neuromuscular control strategies. This factor has led to the absorption of a large reaction force by the knee ligaments during sports activities, which is a factor in placement of the knee in a valgus position.⁹ Results of the studies demonstrate that the increase in knee valgus leads to a change in the function of the lower limbs in frontal plane,¹⁰ which may be caused by changes in contraction patterns of the trunk and hip muscles.¹¹ A study on athletes who suffered from ACL injury suggested that they had 8 degrees more valgus during landing compared to healthy individuals. Valgus loading increases the relative pressure applied to the ACL, and this can lead to ligamentous laxity at high levels.⁸ In this regard, other studies have also shown that individuals with increased valgus are more exposed to ACL injuries when performing dynamic activities.^10,12,13 In general, the specific mechanical behavior of the proximal and distal joints of the middle joint of the lower limb movement chain determines the right or wrong distribution of forces imposed on musculoskeletal system of this joint.¹⁴ Accordingly, the athlete's ability to maintain the correct dynamic alignment of the lower limb segments in movement planes can be a significant factor in occurrence of knee injuries in sports.³

One of the factors that cause lack of proper control of movements in frontal plane of the lower limb is the decrease in muscle strength and defects in the ROM. Reports are indicative of a relationship between the decrease in muscle strength and disorders of motion range and non-contact knee injuries.^15,16Decreased ROM of ankle dorsiflexion¹⁷ and weakness of abductors and external rotators of the hip joint are known to be effective factors in causing DKV defect.¹⁸ Also, dynamic balance along with static balance are complex abilities that result from the coordination and synergy between the vestibular system, visual and proprioception,¹⁹ hence, may be influenced by some variables of neuromuscular function (for instance, the strength of the hip and knee joints, the ROM of the lower limb joints and the stability of the core). ACL injury in athletes is associated with disorders related to balance and postural control.²⁰ Poor balance has been described as a predictor of lower extremity injury in these athletes, and football players with poorer balance are almost twice as likely to suffer lower extremity injury.²¹ Regarding the effect of knee injury on balance, various studies have been conducted that focused on the effect of knee valgus and ACL injury on this variable.²² Neuromuscular factors, functional activities and movement kinematics are adjustable internal variables that affect the non-contact ACL injury.²³

Accordingly, one of the effective ways to reduce the occurrence of ACL injuries is to reduce valgus loading. Specifically, it has been shown that programs focused on neuromuscular variables and increasing proprioception reduce the risk of ACL injury by 51% to 88%²⁴ Regarding the influence and selection of the type of exercise, different studies have been carried out, which have had different effects, such that some studies implied the lack of effect of strength training²⁵ and stretching²⁶ on DKV. Nevertheless, Sasaki et al. (2019) pointed out a significant improvement in biomechanics of landing following the use of core strength training.²⁷ Given the significance of proper rehabilitation and the need to use proper exercises to prevent injuries, the German Knee Society has presented a special exercise program for athletes and non-athletes with knee ACL injuries called STOP X program. It has been reported that these exercise programs can be influential in preventing injury and can reduce knee injuries by 27% and ACL injuries by 51%.²⁸ However, due to the novelty of this training program, the studies conducted are limited; therefore, the present study aims to investigate the effect of Stop X exercises on balance, strength, and range of motion of football players with dynamic knee valgus defect.

participants

This study was a quasi-experimental type, and in terms of its objectives, it was of an applied type, with the code of ethics No. IR.URMIA.REC.1402.018 from the Ethics Committee of Urmia University. The statistical population of the current study included male football players with dynamic knee valgus defect with an age range of 12 to 14 years in Rasht. The samples were purposefully selected from the target society after obtaining consent and were randomly assigned into two control and training groups (15 in each group). Using the sample size estimation software (G*Power), according to the statistical test of analysis of covariance and having a covariate, in alpha of 0.05 and F value of 0.27, the sample size of 15 in each group was considered to obtain a statistical power equal to 0.8, which is suitable for experimental studies. The age range of 12–14 years, having DKV originating from the knee, at least 3 years of regular activity in football and the absence of knee or ankle injuries were among the main inclusion criteria. Absence in 3 sessions of the entire study or two consecutive sessions, unwillingness to continue training and causing pain during training were among the exclusion criteria of the present research.

procedure

To detect the presence or absence of DKV, overhead squat test was performed. Each subject performed five squat tests in a standing position on both legs in a standard condition (feet shoulder-width apart, toes straight forward, hands above the head with elbows locked in extension, knees up to 90° flexion), while the examiner observed them from the front. To minimize the learning effect, no training was allowed before the squat test. If during the movement and performance of 3 squat tests out of 5, the examiner visually observes from the front view that the middle point of the patella of dominant leg passes through the inner part of the big toe, then that subject has DKV. If DKV was observed in this test and after placing a board 5 cm high under the subject's heel, there was still valgus in the squat test, it would be confirmed that the origin of DKV is from the knee area²⁹ (Fig. 1). The validity and reliability of this test were reported as 78% and 73% respectively.³⁰

- please insert Fig. 1 here -

Stork test was used to assess the static balance, such that the subjects stood on their dominant leg and placed toes of the other foot on the knee of the dominant leg while their hands were on their waist. Then, with the command "ready" and then "go", the subjects raised the heel of the dominant leg and while standing on the toes of one foot, they tried to maintain their balance without moving the legs or leaving hands from their waist (Fig. 2). The test was performed 3 times and the best time was recorded as a score.³¹

- please insert Fig. 2 here -

YBT was used to assess the dynamic balance. The method of conducting the test was such that the subject was informed about the implementation of the test through the researcher’s explanation and in order to minimize the learning effects, each subject performed this test six times in three directions as a practice before the main performance. Then, in main performance, the subjects stood on their dominant leg in the center of intersection of the lines, while standing on the dominant leg, the subjects were asked to reach with their free leg in anterior, posterior-internal, and posterior-external directions. The test was performed in such a way that the subject stands on his dominant leg and performed the act of reaching three times in three directions. The distance from the contact point to the center was considered to be the reach distance, measured in centimeters (Fig. 3). This test was repeated twice for each subject and the average was taken; Then, the obtained average was used as leg length. The length of individuals' legs had an effect on their reaching distance. Therefore, to normalize this test, the average reaching distance was divided by the leg length of each subject and multiplied by 100 to calculate the dependent variable and the reaching distance was obtained as a percentage of the leg length.³²

- please insert Fig. 3 here -

Score: Reaching distance/leg length * 100

A manual strength test (MMT, North coast) was used to measure the isometric strength of the muscles (made in USA, unit of measurement is kg, reliability 95–98%). All muscle tests were performed using the method presented by Kendall, (2005).³³ For each strength test, the subject was asked to get into a proper position and was trained to maintain this position. With the help of a strap, the examiner applied a suitable pressure to dynamometer against the force generated by the subject. The maximum generated force was recorded. Each test consisted of 3 contractions of 5 seconds with 30 seconds of rest for each contraction, and the average of repetitions was used for statistical analysis.³³

To measure the strength of hip external rotators, the subject was placed in a sitting position with the hip and knees at 90 degrees. The dynamometer was located 5 cm proximal to the medial malleolus. To control the movements of the upper limbs, the subjects were asked to cross their arms on their chest. In this situation, the subjects performed the external rotation of the hip and the amount of strength in this movement was recorded. The strength of hip abductors was also measured in a position where the subjects were lying on their side on the examination bed while the hip joint of the subject's leg was in extension and the dynamometer was on the side of the hip, at a point of 5 cm above the lateral joint line of the knee. The subject held edge of the bed with his upper hand and the lower hand was under his head in a comfortable position (Fig. 4). They were asked to move their leg upwards with maximum effort 3 times, and 15 seconds rest was considered between each time. The average of all three isometric contractions was recorded in kilograms of force.³³

- please insert Fig. 4 here -

A goniometer was used to measure the range of motion. To this end, to measure hip abduction, the subjects were asked to lie on their back on examination table (supine position). The pelvis was in neutral position and legs were in anatomical position. The examiner fixed the pelvis on the subject's side with one hand and took the distal inner side of the bone with the other hand and gave the hip abduction movement and taught the subject how to abduct the hip. Then, the subject was asked to actively perform hip abduction. The center of the goniometer was placed on the ASIS on the side to be measured, the fixed arm was in line with the line that connected the right and left ASIS, and the movable arm was parallel to the longitudinal axis of the hip towards the mid-line of the patella. At the starting point, the goniometer showed 90 degrees, which was taken as zero.³⁴ In assessing the hip external rotation range of motion, the subjects were asked to sit on edge of the examination table, while the knee was in 90 degrees flexion and hip was in zero degrees abduction and adduction and 90 degrees flexion. Then, they actively performed external rotation. The center of the goniometer was above the anterior part of the patella, the moving arm was along the midline of the leg, and the fixed arm was perpendicular to the ground ³⁴ (Fig. 5).

- please insert Fig. 5 here -

The training program used in this study was the Stop X training program.²⁸ This program consists of running, balance training, landing-jump pattern and strength training. It was carried out for 8 weeks, 30 to 40 minutes and 3 times a week. Athletes started with simple exercises, and the level of difficulty of individual exercises increased over time.

Descriptive and inferential statistical methods were used to analyze the collected data. Shapiro-Wilk test was used to check normality of data distribution. Analysis of covariance and dependent t-tests were used to compare the mean of research variables between and within groups, respectively. All statistical operations were performed by SPSS version 24 software.

The mean and standard deviation of the subjects' individual characteristics, including age, height, weight and body mass index (BMI) are provided in Table 1.

Table 1

Demographic characteristics of the subjects
Index	control (n = 15)	Training (n = 15)	P value
Age (year)	12.73 ± 0.88	13.00 ± 0.92	0.42
Height (m)	1.60 ± 0.03	1.61 ± 0.04	0.33
Weight (Kg)	52.06 ± 4.92	54.26 ± 3.84	0.18
Body mass index (kg/m²)	20.22 ± 1.68	20.77 ± 1.23	0.32

- please insert Table 1 here -

Results of the independent t-test in examining the homogeneity of the variables proved homogeneity of the descriptive variables in two groups. Given the normality of the data, determined by Shapiro-Wilk test, analysis of covariance and dependent t-test were used to compare between and within groups. Results of the dependent t-test were presented in Table 2.

Table 2

Dependent t-test results for intra-group comparison of strength, range of motion, static and dynamic balance
Group	Control				Training
Group	Pre-test	Post-test	T	P	Pre-test	Post-test	T	P
Hip abduction strength (N)	19.22 ± 5.47	20.43 ± 5.18	-1.82	0.08	25.92 ± 11.47	33.61 ± 9.79	-976	0.001^**
Hip external rotation strength (N)	9.22 ± 2.79	10.24 ± 3.23	-1.72	0.10	10.86 ± 4.67	15.79 ± 4.46	-10.85	0.001^**
Hip abduction ROM (°)	43.73 ± 4.87	44.46 ± 4.58	-1.43	0.17	45.26 ± 6.64	49.13 ± 4.71	-3.01	0.009^**
Hip external rotation ROM (°)	42.43 ± 4.50	43.20 ± 4.29	-1.34	0.19	44.00 ± 6.17	47.26 ± 4.89	-3.25	0.006^**
Static balance (s)	6.22 ± 1.28	6.41 ± 1.24	-2.03	0.06	6.54 ± 1.42	7.92 ± 2.23	-4.73	0.001^**
Anterior direction of YBT (% limb length)	59.90 ± 8.93	61.06 ± 10.27	-1.87	0.08	58.81 ± 11.24	65.49 ± 10.47	-5.55	0.001^**
Posteriomedial direction of YBT (% limb length)	74.43 ± 7.33	75.77 ± 8.66	-1.59	0.13	75.61 ± 5.45	81.91 ± 7.39	-7.65	0.001^**
Posteriolateral direction of YBT (% limb length)	70.86 ± 8.24	71.48 ± 8.23	-1.32	0.20	74.51 ± 8.98	78.75 ± 8.96	-18.69	0.001^**
Total score of YBT (% limb length)	68.40 ± 4.52	69.44 ± 5.00	-2.73	0.01	69.64 ± 3.16	75.38 ± 3.62	-11.83	0.001^**
**Sig. at p < 0.01

- please insert Table 2 here -

Results of dependent t-test indicate a significant effect of Stop X training program on the results of hip abduction strength (p = 0.005), hip external rotation strength (p = 0.001), hip abduction range of motion (p = 0.009), hip external rotation range of motion (p = 0.006), static balance, and dynamic balance (p = 0.001) of subjects in training group. However, no significant difference was observed between pre-test and post-test in control group (p < 0.05). Results of the analysis of covariance test were also presented in Table 3 for inter-group comparison.

Table 3

Results of covariance analysis for inter-group comparison of strength, range of motion, static and dynamic balance
Variable	Test stage	Group	Mean ¥	F	df	p	Eta squared
Hip abduction strength (N)	Post-test	Control	23.12	41.35	1	0.001^**	0.60
Hip abduction strength (N)	Post-test	Training	30.92	41.35	1	0.001^**	0.60
Hip external rotation strength (N)	Post-test	Control	10.96	29.76	1	0.001^**	0.52
Hip external rotation strength (N)	Post-test	Training	15.08	29.76	1	0.001^**	0.52
Hip abduction ROM (°)	Post-test	Control	44.93	10.91	1	0.006^**	0.28
Hip abduction ROM (°)	Post-test	Training	48.66	10.91	1	0.006^**	0.28
Hip external rotation ROM (°)	post-test	Control	43.71	9.64	1	0.004^**	0.26
Hip external rotation ROM (°)	Post-test	Training	46.75	9.64	1	0.004^**	0.26
Static balance (s)	Post-test	Control	6.60	14.46	1	0.001^**	0.34
Static balance (s)	Post-test	Training	7.73	14.46	1	0.001^**	0.34
Total score of YBT (% limb length)	Post-test	Control	70.08	53.67	1	0.001^**	0.66
Total score of YBT (% limb length)	Post-test	Training	74.75	53.67	1	0.001^**	0.66
¥ Adapted based on pre-test values; **Sig. at p < 0.01

- please insert Table 3 here -

Results of the covariance analysis test suggest that there is a significant difference between the two groups in the results of hip abduction strength (P = 0.001), hip external rotation strength (P = 0.001), hip abduction range of motion (P = 0.003), hip external rotation range of motion (P = 0.004), static and dynamic balance (P = 0.001), such that the value of these components in training group has increased significantly compared to the control group.

The current study was conducted to investigate the impact of stop X training program on balance, strength and range of motion of football players with dynamic knee valgus defect. The obtained results demonstrate that after eight weeks of implementation of the training program, a significant difference was found in balance, strength and range of motion between the subjects of two training and control groups.

Results of the present study regarding static and dynamic balance have approved the effect of Stop X exercises on improving the static and dynamic balance of athletes with dynamic knee valgus. Balance exercises activate different parts of the nervous system that play a role in stability of the joints and improve the performance of sensory-motor and neuro-muscular system. Accordingly, these exercises may further reduce the time required to receive sensory stimulation and motor responses.³⁵ One of the possible reasons for the increase in balance in training group is the increase in strength of the lower limb muscles after training program, the process of reducing inhibition and stimulation of muscle spindles during strength training.³⁶ Also, improvement of neuromuscular control after training can be effective in reducing the knee valgus angle. In this regard, it was stated that strengthening muscles of the trunk, legs and the proprioception of the soles of the feet are effective in improving balance.^37,38 Trunk exercises have special training effects that strengthen balance,³⁹ and unstable training devices such as balance boards and soft foam strengthen proprioception, improve muscle coordination and leg muscles, and ultimately improve balance.⁴⁰ Considering that it takes 40 milliseconds to create enough hamstring tension to prevent injury or stabilize the knee, and the ligament-muscle reflex is slow to prevent anterior cruciate ligament tears, improving balance can be one of the factors to reduce the risk of anterior cruciate ligament injury.³⁹ In general, based on the obtained results in this field, it seems that the use of Stop X training program can be effective in improving the balance of athletes with dynamic knee valgus.

Results of the study showed that Stop X training program has a significant effect on increasing the strength of hip abduction and hip external rotation of football players with dynamic knee valgus defects. Regarding the importance of hip muscle strength in knee and hip movement, it should be stated that hip, as a proximal joint of the lower limb, provides bone stability, though it depends on a complex interaction of muscle activity to create dynamic stability during movement. In activities such as running or landing, external forces acting on the hip joint create flexion, adduction, and internal rotation, known as lower limb valgus.²⁹ These forces created by internal forces are controlled by hip extensors, abductors and external rotators.⁴¹ Disruption in force production of these muscles may increase the range of hip adduction and internal rotation during weight-bearing movements, potentially affecting kinematics of the entire lower limb.²⁹ In this regard, studies show that regular resistance exercises can have a significant impact on increasing muscle strength and hypertrophy regardless of age and gender.⁴² It has been stated that the adaptation of strength in initial phase is mainly related to the improvement of the ability of the nervous system in muscle activation and coordination, while the role of hypertrophy for strength increases with experience.⁴³ Regarding the effects of plyometric exercises, Myer et al. (2006) pointed out the effect of plyometric exercises on improving the strength of hamstring muscles⁴⁴ and Bonacci et al. (2011) focused on the effect of plyometric exercises on activation of leg muscles after 6 weeks.⁴⁵ In general, according to the results, it seems that Stop X exercises have a significant effect on improving muscle strength, and accordingly, the use of this training program to create muscle balance in athletes with dynamic knee valgus is recommended.

Results of the current study on the range of motion of hip abduction and hip external rotation showed that the use of Stop X exercises is associated with an increase in the range of motion in these two situations. Although the exact mechanism of stretching efficiency is not fully understood, it is believed that stretching leads to both mechanical and neural adaptations and increases range of motion.⁴⁶ It seems that mechanical stretching has affected the viscoelastic components of the neurofascial tissue,⁴⁶ and more specifically, a possible decrease in passive resistance of the muscle against the stretching force, present throughout the range of motion, is observed.²⁶ Neurologically, it seems that static stretching of the neurofascial tissue to the end of the range of motion, probably through the inhibitory effects caused by Golgi tendon organ (automatic inhibition) and with the reflexive inhibition, reduces the excitability of the motor neuron.⁴⁶ In general, these cases can reduce the sensitivity of stretch reflexes and increase the tolerance to stretch, and thus provide the possibility of increasing range of motion. Also, the application of stretching and exercise in this study may lead to the release of spasm and breaking of adhesions present in short tissue, in this way, it can potentially improve tissue's ability to increase the length and range of motion of the joint.²⁶ In general, the increased range of motion observed in hip movements can be related to these cases. In general, the increased range of motion observed in hip movements can be related to these cases. The application of stretching exercises in the programs of this study to release the shortened tissues and obtain the desired range of motion in athletes with DKV defect can be associated with the improvement of the range of hip motion.

In general, results of the present research reflected the effect of Stop X exercises on increasing the strength and range of motion of the hip, as well as improving static and dynamic balance of football players with dynamic knee valgus, thus, indicating the significance of using these exercises to improve the performance of these athletes.

ROM

range of motion

DKV

dynamic knee valgus

YBT

Y-balance test

ACL

anterior cruciate ligament.

Ethics approval and informed consent to participate

All experimental protocols of this study were carried out following Declaration Helsinki and were approved by the Ethics Committee of Urmia University (Approval No. IR.URMIA.REC.1402.018). All subjects provided written information informed consent prior to participation in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Funding

This study did not have any funds

Availability of data and materials

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request

Authors' contributions

RH: Investigation, Conceptualization, Methodology, Data capture, Data analysis.

EM: Writing- Original draft preparation, Data curation, Conceptualization, Scientific editing.

SR: Writing- Original draft preparation, Investigation, Data capture, Date analysis.

Acknowledgements

The authors would like to thank all participants in the collaboration to make this study.

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No competing interests reported.

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The effect of stop X exercises on balance, strength and range of motion of football players with dynamic knee valgus defect

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