Training and Recommendations on the Lower Limbs Exp losive Force of Juvenile Amateur M en Sprinters

Jingwen LI，Kaikai REN，Zhenglin CAO，Zheng LI

1.College of Physical Education，Southwest University，Chongqing 400715，China；2.Center of Agricultural Education and Development Research，Southwest University，Chongqing 400715，China

Sprint，one of the oldest sports competition events，is the most intense and highly spectator sport among all track－and－field competition events.With the development of science and technology，various advanced scientific theory and technique as well as equipment are applied to exercise training.Training of athletes is getting increasingly scientific，scores of sprinters are getting higher，and the world record is broken constantly.

Sprint can reflect and represent a country's track－and－field level.In China，sprinters are in a lower level in the world in terms of physical fitness and technique［1］.A lack of lower limbs explosive force is one main reason.Though there are a lot of domestic and international discussions about sprinters'lower limbs explosive force now，there is still a large gap among athletes at different ages and from different countries in terms of physical fitness and characteristics.In China，many juvenile sprinters imitate excellent foreign athletes blindly in the training in lower limbs explosive force without considering their own characteristics，which would hinders them from improving sports level.Personally speaking，I do wish to help juvenile sprinters in terms of training in lower limbs explosive force by discussing Chinese sprinters'lower limbs explosive force.

1　Explosive Force and Training Requirements

Physical strength is an ability to overcome or fight against resistance when body's neuromuscular control system works as well as an impetus to carry out and complete actions for the human body［2］.The strength sprinters need is not the absolute force of muscles，but the explosive force produced by fast-contracting muscles［3］.Explosive force is one way to show human body's quick force，and an important basis for many strength-type sports events.Because athletes'explosive force is crucial to their scores，coaches always attach great importance to the development of athletes'explosive force in the training.Anaerobic supplement is the focus of sprint，which is a perfect combination of speed，strength as well as technique.

Explosive force is the most important part of quick force，and sprinters'lower limb explosive force level would affect their scores.In strength－oriented training，physiological and biochemical properties must be considered.Besides，structural or formal similarity between strength'smovement structure and specific actions should be paid attention to in the training as well［4］.Six principles should be followed in the training：

（i）Force must keep consistent with skilled movement in the strength training.

（ii）Exercise amplitude（joint angle）must keep consistent with skilled movement in the strength training.

（iii）Skilled movement requires the part using the maximum force must bear the maximum overloading in the strength training.

（iv）Force in the exercise must exceed force in the movement technique when performing exercise，namely overloading exercise is required.

（v）Movement speed must be guaranteed in the strength training，namely explosive actions should be involved.

In order to better compare differences caused by different training methods of juvenile amateur men sprinters and seek for a better training method for them，we take the track－and－field team in Jianshan High School in Chongqing as an experimental object to compare training methods.

2　Experimental objects and methods

2.1Experimental objects Twenty men sprinters，selected from the track－and－field team in Jianshan High School in Chongqing，are divided into two groups（A group and B group）by draw method.A group is the experimental group and B group the control group.Each has10 sprinters.In the training，the experimental group（A group）adopts a combined method giving priority over one-legged training while the control group（B group）adopts a combined method giving priority over double-legged training.

Basic Information（Table 1）and Basic Quality Indicators（Table 2）of the Experimental Group and Control Group before the Experiment.

Table 1 Basic Information before the experiment

Table 2 Basic quality indicators before experiment

2.2Experimental methods

2.2.1 Experimental time.The experimental time goes from April to June in 2011，which is three months in total.Training is arranged in the afternoon four days a week.Training content on Wednesday and Friday is the experimental content，and each training continues 80 minutes.Warm-up exercises should be done 15 minutes before the training，then training would start by groups.The experimental group would do combined exercises giving priority over one-legged training while the control group would do combined exercises giving priority over double-legged training.Relaxation training is arranged in the last15minutes each time.

2.2.2 Testing time.Before the Experiment：A week before A-pril1st.After the Experiment：A week after June 1st.Tests before and after the experiment must be conducted rigorously in the same conditions.The test site，instruments and order must remain the same in the two tests.Testing indicators mainly involve speed and explosive force indicators，as shown in Table 3.

Table 3 Testing indicators

2.2.3 Theory of the training method.Bounce training is the mainmethod in juveniles'lower limbs explosive force training.In order to make them more active in the training，both combined exercises giving priority over one-legged training and combined exercises giving priority over double-legged training can be adopted［5］.According to juveniles'characteristics，exercises giving priority over one-legged training contain the short distance hops or steps，one-legged steps jump，one-legged heel lift，one-legged tuck jump，one-legged weight bearing squat，and squat jump，etc.while exercises giving priority over double-legged training contain vertical jump，tuck jump，leapfrog，double-legged hurdle jump，double-legged drop jump，double-legged steps jump，and standing long jump，etc.

Juvenile sprinters are lack of training sense when performing amateur training.In order to improve athletes'scores，coaches mainly exert the training method adopted by excellent adult athletes in the training，which focuses on barbell.The research reveals that full squatting and squatting loading exercises with barbells could increase athletes'scores to some degree.However，as their abilities improve，an increase of the load will impede increasing scores.

Loading exercises with barbells mainly focus on applying force vertically，which has some differences from the direction and angle of exerting force when running.Exercises with barbells can effectively improve the force of quadriceps femoris and muscles group in the back of calf，can improve human body's ability to move upwards，but cannot improve the explosive force of muscles group in the back of thigh and muscles group in the fore of calf，which is not good for the coordinated development of muscles group in the fore or back of thigh and calf.Thus，the coordination of movement would be affected and athletes cannot effectively improve their scores on sprint.

Rapid flexion and extension of hip joint is an outstanding characteristic of modern dash skills.Loading exercises with barbells cannot improve muscle strength of hip joint，and it can also affect the flexion－extension velocity and amplitude of hip joint when running at high speed.Sprinters'supporting time is from about0.08 seconds to 0.11 seconds，while exerting time of barbell exercises is from about0.4 seconds to0.5 seconds.Thus，the latter one is much longer than the former one.

If athletes take one-legged squat exercises without loading，they are just using their weights as barbells.In this way，the spinal column would not bear pressure from barbells，so they can act faster and gain a better training effect.According to the supporting condition，jumping exercises could be divided into hops exercises and steps exercises.They have different dynamic characteristics and different influences on every joint and muscle of lower limbs，so they would improve athletes'lower limbs explosive force differently.

According to the above analysis，this experiment employs a control experiment between a combined exercise giving priority over one-legged training and a combined exercise giving priority over double-legged training to test which one can better improve juvenile sprinters'lower limbs explosive force.

2.2.4 Training methods.Table4will show the training methods carried out by the experimental group and control group respectively.

Table4 Experimental group and control group：Table of training methods

2.2.5 Weight training and requirements.Table 6 includes training arrangements which have taken training diversity and specific performance of the youth into account.

Table 5 Experimental group：training arrangement table

Table 6 Control group：Training arrangement Table

3　Results and analysis

3.1Analyzing and contrasting the experimental group's indicators before and after experiment

3.1.1 Analyzing and contrasting speed indicators before and after experiment.

Table 7 Speed indicators Table before and after experiment

60-meter sprint is the most effective way to testify the professional qualities of an athlete.American sport expert Gary suggests：＂six－second－theory means when people do their utmost to run forward，then，they are able to achieve the fastest speed within 6 seconds regardless of their given capability；in all，it can be about50－60meters in six seconds.＂

The data from the Table 7 proves that the average time of athletes'60-meter sprint has significantly decreased by 0.27 seconds after three months'training.

We have improved athletes'explosive force of their thigh muscles at the start point of crouch sprint and through acceleration sprint and strengthened the dynamic force caused by high－speed alternation of hip，knee and ankle joints，which will activate their motionless potentials.

After the sprinters are trained to support their body weight by only one leg without any other extra load，so as to increase their body load capacity as well，the experiment has indirectly built up their speed；it has not only improved the explosive force of joints of lower limbs and toes muscles，but also shortened the buffer time of touchdown.

The result shows the training methods taken by the experimental group can largely improve sprinters'performance of better start and acceleration.

3.1.2 Analyzing and contrasting explosive force data before and after experiment.

Table 8 Experimental Group：Table of Explosive force before and after experiment

Sprint requires a high-level of athletes'explosive force of lower limbs，balance and coordination while standing long jumping focuses on their explosive force.The experimental group having been trained for 3 months，their performance is largely raised by 0.14meter on average.This result is achieved by consecutive explosive force of effective cooperative work of extensors of hip and knee joints and flexors of ankle joints.It shows that the training method carried by this group can help boost lower-limb explosive force of athletes.

3.2Analyzing and contrasting data of the control group before and after the experiment

3.2.1 Analyzing and contrasting speed data before and after the experiment.

Table9 Control Group：Speed Data before and after Experiment

After the training，the result that the average time of60-meter－crouch－start sprint falls by 0.15 seconds demonstrates trainees'ability to start and accelerate has been remarkably boosted through this method of training.

The method taken by control group is mainly dependent on the flexion and extension of vertical multi－joints.Moreover，the research indicates it is effective for the youth trainees to drop jump under0.7-meter high；however according to their specific physical features of the youth，the height is 0.4 meter.In addition to the jump practice，the trainees continue to undertake the print.；the method has improved both the links between jump and print practice but athletes'sprint speed due to better force converse.

3.2.2 Explosive force indicators before and after experiment.

Table 10 Control group：Table of exp losive force before and after experiment

After the experiment，the result，which of the long jump has increased 0.06 meter，indicates the training method can improve athletes'explosive force of their lower-limbs.Drop jump and successive hurdle－jump emphasize the touchdown of the sole's former part instead of the flexion or extension of knee joints；hence，itwill improve the super－equal-length contractility of knee and ankle joint muscles.

3.3Analyzing data from both groups before and after experiment

3.3.1 Analyzing and contrasting speed data before and after experiment.Generally speaking，although methods adopted by the two groups consist of various training practices and their results of 60-meter-run have obtained some improvement，the experimental group has a better performance that the control group.；it shows that methods of both make a contribution to build up athletes'speed，but obliviously the experimental works better.

3.3.2 Analyzing and contrasting explosive force data before and after experiment.In the same way，both present an improved performance of explosive force but the experimental group better because different weight practices of super－equal-length impact the force variously.The result drawn by researchers such as Jing Xianglan demonstrates：＂super－equal-length practice free from weight lead to the development of the explosive force of knee joints while super－equal-length practice with light weight results in many effective consequences that boost the absolute and explosive force of lower-limbs and that of the muscle of knee joints as well.＂

4　Conclusions and recommendations

4.1Conclusions Based on the training and experiment above，the paper can conclusion as follows：（i）as indicators from both groups have been improved through the training，therefore，it is proved that the methods taken by both play an important role on the improvement of athletes'lower-limbs'explosive force；（ii）the results of analysis show although the structure feature and ways of muscle strength exertion is similar to the characteristics of professional skills，however，the larger the effective transformation between all qualities is，the better the performance will be.No matter jump，hop，or any other similar practice，all of which share some common features or operations of muscles with sprint，therefore，it serves as a effective way to develop the professional qualities of juvenile sprinters.

4.2Recommendations According to the experiment of explosive force of juvenile amateur men sprinters and its conclusions，in order to improve the training methods，the paper carries forward four recommendations：

（i）In order to discover proper methods to enhance the explosive force of juvenile amateur men sprinters，we can raise the ratio of hop practice so that we can offer pertinent and comprehensive training to the youth.

（ii）Correspondent developments of various muscles should be taken into consideration during the training.Professional competition not only requires the powerful strength of large and main muscle groups，but also that of the small，distal and deep muscle groups.

（iii）The training should follow in proper sequence and make steady progress；meanwhile，it should also pay attention to the practice of upper-limbs'explosive force，speed and endurance.

（iv）As experimental subjects are the juvenile men sprinters in high school，whose skill levels and endurance are very limited，hence the results can merely be taken as reference for other athletes with lower or higher levels.

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