This study specified the locomotion characteristics of a group of male third-grade students divided into groups by their cardiorespiratory endurance levels as estimated by a 20-m shuttle run. The 20-m shuttle run was developed in 1984 as a non-gas analytical test method and is the most widely used method of estimating cardiorespiratory endurance. In addition, it is used as the primary method of the United States’ student fitness measurement program (FitnessGram)33,34,35.
The locomotion characteristics show differences depending on age and gender. Males generally have faster locomotion speeds than females, and also have less cadence and longer stride length. The locomotion speed of children and the elderly is also slower than that of adults24,36. Many studies have reported on the relationship between physical fitness and spatial-temporal locomotion parameters37,38,39. In particular, this study’s critical keyword for cardiorespiratory endurance and locomotion variables is energy expenditure. In a related study, when performing locomotion at the same speed, adolescents had a higher VO2 Max than both adults and the elderly and also showed significantly greater energy expenditure at slower speeds than faster ones24,40. The fact that these results were found in adolescents who do not have locomotion disorders, when compared with the elderly, shows that their method of locomotion is different from that of adults and the elderly.
By comparing the locomotion characteristics between the two groups divided by cardiorespiratory endurance level, all locomotion variables in this study were found to be statistically significant in the average difference according to the locomotion speed. Furthermore, when comparing the two groups, the single support phase, double support phase, and time of toe-off variables all showed significant differences for each locomotion speed. Likewise, the range of motion inversion/eversion variable showed significant differences between the groups at slow locomotion speed.
This study is unique in that it compares the locomotion characteristics of the two groups by applying a locomotion differential speed protocol based on cardiorespiratory endurance standards for adolescents. When walking speed, single support phase, double support phase, time of toe-off, and inversion/eversion ROM of the foot was compared with the results of using the differential speed, and the results between groups, the locomotion of adolescents show different characteristics depending on their cardiorespiratory endurance level. In particular, the locomotion of adolescents shows more distinct characteristics according to the locomotion speed. Therefore, this study's main conclusion is that adolescents' locomotion characteristics vary according to their level of physical strength, particularly cardiorespiratory endurance. At the same time, significant differences were also found during slow locomotion speed among the single support phase, double support phase, time of toe-off, and inversion/eversion variables.
Additionally, and again depending on cardiorespiratory endurance levels, walking speeds showed a statistically significant difference at fast speeds, consistent with the results of previous studies that showed a correlation between physical fitness level and walking speed at maximal speed41. In particular, walking speed was shown to be strongly associated with muscle strength, agility, and dynamic balance, and strengthening these physical factors increased walking speed42,43,44. The group standard of this study was the cardiorespiratory endurance level, and it was found that adolescents with better cardiorespiratory fitness had faster walking speeds. Also, unlike the locomotion cycle and range of motion, there was a group difference in walking speed at fast locomotion speed, so it was found that the fitness level of adolescents could be confirmed at fast locomotion speed.
The longer it takes for the single support phase to converge to 40%, the shorter the time that the double support phase converges to 20%, and the shorter the time of toe-off converges to 60%. The more efficiently managed energy expenditure is considered healthy for muscle, equilibrium, and neurological function. In addition, if the ROM of inversion/eversion is less than − 7° or greater than − 4°, then there are likely to be difficulties with muscle nerves and muscle coordination38,39,45. Based on these locomotion characteristics study results, analyzing the results showed statistically significant differences between the groups; the EG group showed more standard locomotion characteristics in the single support phase, double support phase, and time of toe-off—trends that became more apparent as the locomotion speed increased.
However, the inversion/eversion of the foot was smaller than the standard range of motion in healthy adults in both groups, and both groups also showed a tendency for eversion during locomotion. In addition, the dorsi/plantar flexion of the foot was smaller than the standard range of motion in healthy adults, although the difference was not statistically significant. The reason for this is that adolescents are in their growing period, and have an imbalance in ligament and muscle length due to the rapid growth of their bones46. In the locomotion cycle of adults, maximum eversion appears mid-stance. However, the relatively small eversion in the adolescents in this study showed that the agonist actions of the peroneus longus, peroneus brevis, extensor digitorum longus, and extensor hallucis longus were sufficient during locomotion. Also, it was thought that the agonist action of the tibialis posterior, tibialis anterior, flexor hallucis longus, and soleus was also not working properly47,48,49,50,51. The reason for this is that the lower leg muscles lose flexibility and the hamstrings tighten as a result of the limited hip joint ROM in adolescents. This leads to an imbalance in the contraction of the lower leg muscles52, 53,54,55,56,57. In summary, when performing locomotion, there is an imbalance in muscle activity in the lower extremities due to a decrease in muscle flexibility during the growth phase. Consequently, the locomotion characteristics of adolescents have a lower level of coordination than adults, and they form inefficient locomotion characteristics of the lower extremities.
However, it should be noted that in this study, the adolescents with excellent cardiorespiratory endurance levels showed inversion characteristics at a slow locomotion speed, unlike the NEG. Also, single support, double support, and time of toe-off showed characteristics closer to normal. Previous studies show that adolescents in the growing phase maintain locomotion stability even though they do not show a normal pattern of locomotion characteristics compared with adults. In addition, it was shown that adolescents with good cardiorespiratory endurance performed a normal locomotion cycle similar to the locomotion characteristics of adults by controlling locomotion by central control of the neural networks of movement, despite the limitations in the ROM of the lower extremities due to growth. The results suggest that the higher the cardiorespiratory endurance level, the more pronounced this pattern58,59,60. In addition, although physical changes in the lower extremities of adolescents in the growth period can negatively affect locomotion performance, locomotion control can maintain stability through central control and mitigate unstable performance61. Moreover, the most statistically significant locomotion characteristics of adolescents according to cardiorespiratory endurance level were in line with previous similar studies. Compared to children, adults, and the elderly, growing adolescents showed more inefficient characteristics related to energy consumption when performing slow locomotion24,40.
Among the variables in this study, cadence, normalized stride length, and step length did not show any differences between groups or when compared with the normal locomotion characteristics of adults; they appeared to belong to the out-of-the-standard category. In addition, the adduction/abduction range of motion showed a pattern similar to that of the normal adult range at all locomotion speeds. Therefore, this study found that adolescents with high cardiorespiratory endurance levels showed relatively normal characteristics in the locomotion cycle phase compared with adolescents with low cardiorespiratory endurance levels. However, both groups tended to invert more during locomotion because their flexibility and coordination deteriorated with growth, although the EG showed a more pronounced tendency.
What is noteworthy here is that there was a clear difference between the groups at slow locomotion speeds, and the adolescents in the growing stage showed an inefficient pattern in terms of energy expenditure at slow locomotion compared to children, adults, and the elderly. In particular, our results showed that the locomotion characteristics differed at slow speeds depending on the cardiorespiratory endurance level. A clear difference, found only during fast locomotion, was that the locomotion characteristics of adolescents were more pronounced at the slow locomotion speed.
Limitations
One limitation of our study is that the locomotion speed of adolescents reflected the general speed of adults. In a follow-up study, if each adolescent's preferred speed is measured and reflected in the experiment, we will be able to obtain more detailed characteristics. In this study, VO2 Max 60ml/kg/min was used as the standard, and it is believed that a more in-depth analysis would have been possible if other physical attributes of the students were considered in addition to VO2 Max, were considered.