Musculotendinous injuries are shown to be responsible for a significant proportion of injuries incurred by athletes. The injuries have a high incidence of recurrence. In addition, warm up is considered to be important in preventing muscle injuries by increasing the elasticity of muscles and smoothing muscle contraction .
Stretching exercises help to relieve stress as they get the blood flowing - improving circulation while increasing flexibility and relieving muscle tension. Stretching exercises also stimulate receptors in the nervous system that decrease the production of stress hormones. Typically, two different types of warm up protocols were presented: static and dynamic.
Although static stretching has been theorized to enhance performance , a number of authors have reported that an acute bout of pre-exercise static stretching may actually reduce anaerobic performance in adults through decreases in force and power [10, 19]. Also it has been shown that long term static stretching increases the range of motion at a particular joint, but it appears that warm up protocols, including prolonged static stretching might have unintended adverse consequences on anaerobic performance in young athletes .
Robbins  suggeste]d that warm up with dynamic exercise may create an optimal environment for power production by enhancing neuromuscular function. This phenomenon has been referred to as postactivation potentiation (PAP) and is believed to improve power performance. Dynamic stretching consists of function based exercises which use sport specific movements to prepare the body for movement. Dynamic stretching involves moving parts of body and gradually increases reach, speed of movement or both. It consists of controlled leg and arm swings that take to the limits of range of motion. There are no bounces or jerky movements.
It has been shown  that blood lactate concentration is an index of anaerobic metabolism. It reflects the difference between the rate of appearance and the rate of removal of lactate. Astrand et al. , Gupta et al  and Ghosh et al  discussed that intense muscular activity creates an imbalance in the production and removal of lactic acid within the muscle resulting in diffusion of lactate into the blood and increased blood lactate concentration. The diffusion of lactate is observed 3-10 minutes after the cessation of exercise.
Bishop et al  recommended that endurance performance be influenced by two important factors in a specific exercise mode: a) maximum capacity to consume O2 (VO2max), b) maximum level for steady rate exercises (OBLA). They have used VO2max as the yard stick to gauge capacity for endurance exercise.
Although this measure generally relates to exercise performance, it does not fully explain success, because one does not perform endurance exercise at VO2max. The exercise intensity at the point of OBLA consistently and powerfully predicts endurance exercise performance in men and women.
Previous authors have compared the acute effects of pre-event static stretching and dynamic exercise on anaerobic performance of youths. Whether stretching exercises and dynamic warm up exercises have any effect on blood lactate concentration and VO2max is an intriguing question. In sports even small change in performance can have a drastic effect on the outcome of an event. The purpose of this study was to determine the effects of three different warm up protocols on some endurance performance indices.
Materials and Methods
Fifteen healthy untrained males (age 21.37 ± 0.4 years; height 176.16 ± 1.06 cm, weight 70.48 ± 1.96 kg), were familiarized with the experimental protocol and informed about the possible risk and benefit involved with the study both verbally and in writing before obtaining written consent. Only healthy subjects without any history of pathology or orthopedic limitation were inducted in the study.
Furthermore, VO2max more than or equal to 40 ml/kg/min was determined as minimal aerobic capacity in order for one to be included in the study. The study was approved by Institutional Medical Ethics Committee. The three warm up protocols with concomitant endurance exercises were performed in random order with the 2 days' gap in between to facilitate recovery. Each warm up protocol lasted a total of 12 min of which first 5 min consisted of jogging at a “comfortable pace”. In control group, subjects performed only jogging. The sequence in which all the 3 protocols (PI, PII, PIII) were performed was different for each subject. Subject 1 was assigned to control group on day 1, followed by PI, PII and PIII. Subject 2, after control group readings, was assigned to PII followed by PIII and PI. This sequence was carried on to the next subject and so on. Dependent variables were blood lactate, VO2max and treadmill time to exhaustion.
Warm up Protocols
Protocol I – Static Stretching
Protocol consisted of 5 min of jogging and 7 min of static stretching for the major muscle groups of lower limbs (Table 1). The subjects performed 4 stretches in a slow and deliberate manner. Subjects held each stretch for 20 seconds at a point of mild discomfort, relaxed for 5 seconds and then repeated the same stretch for another 20 seconds before progressing to the other extremity.
Protocol II – Dynamic Exercises
The protocol consisted of 6 dynamic exercises that progressed from moderate intensity to high intensity (Table 2). The subjects performed each dynamic exercise for one minute and rested about 10 sec.
Protocol III – Dynamic Stretching
Protocol consisted of dynamic stretching exercises. The subjects performed dynamic stretches in a slow and deliberate manner (Table 3).
Table 1. Static stretching
Table 2. Dynamic exercises
Two days prior to the experiment, subjects were familiarized with the experimental setting and protocol. This was done to obtain a pure physiological response as performing for the second time reduces the energy cost and anxiety. Subjects were instructed not to engage in heavy physical activities 24 hours before attending the experimental setting.
On the day of the experiment, the subjects were on the same balanced diet as 48 hours before testing to ensure similar liver and muscle glycogen store. The subjects consumed a similar meal for a minimum of 3 hours prior to the test. On arrival heart rate was recorded with polar heart rate monitor after 15 minutes of rest. Fresh blood sample was collected from the finger tip for pre blood lactate concentration which was analyzed in P-LM5 lactate analyzer (Analox, London). Subjects then performed one of the assigned warm up protocols following 5 minutes of jogging at comfortable pace.
In control group the subjects performed only jogging. After 2 minutes of rest Queen’s College step test was conducted. Subject then underwent moderate intensity exercise consisting of motorized treadmill running at an intensity of 65-75% of HR till exhaustion which was continuously monitored by polar heart rate short range telemetry.
Table 3. Dynamic stretching
We took a wide range of HRR because when performed at the same intensity, the task may pose a considerable stress for one person yet fall short of the training threshold for another. The target maximal heart rate was calculated for each subject, using Karvonen’s formula .
Target Heart Rate = HRrest + required % (HRmax – HRrest)
Where HRmax = 220 – age
The subject’s unwillingness to continue running was considered the point of exhaustion. Total time and distance of the treadmill running were noted at the end. Blood sample was taken 3 minutes post exercise for blood lactate concentration.
All data are presented as the mean ± standard deviation (SD). The data were analyzed for statistical significance by using the statistical package for social sciences (SPSS 14.0) software. Paired student’s t’ test, one way ANOVA and post hoc multiple Scheffe analysis were used.
Blood lactate - Comparison of baseline values of blood lactate shows non significant differences in all protocols (p>0.05). One way ANOVA analysis of post blood lactate values of three different protocols reveals statistically significant difference in blood lactate concentration (F=10.24, p<0.001), with post hoc scheffe analysis revealing that protocol PII induced lower blood lactate values than protocols PI & PIII (Table 4, Figure 1).
Table 4. ANOVA for Blood Lactate Concentration
Figure 1. Comparison of post mean values for blood lactate concentration of control and various warm up protocols
VO2max - One way ANOVA analysis of three different protocols reveals statistically significant difference in VO2max (F=5.18, p<0.01) with post hoc scheffe analysis revealing that protocol PII induced higher VO2max values than protocols PI & PIII (Table 5, Figure 2).
Table 5. ANOVA for VO2max
Figure 2. Comparison of mean values of VO2max of control and various warm up protocols
Time to Exhaustion - One way ANOVA analysis reveals statistically significant difference in time to exhaustion (F=7.45, p<0.001) with post hoc scheffe analysis revealing protocol PII induced increased time to exhaustion in comparison with protocols PI & PIII (Table 6, Figure 3).
Table 6. ANOVA for Time to Exhaustion
Figure 3. ANOVA for Time to Exhaustion
The results of this study demonstrated that warm up with dynamic exercise induced better endurance indices than warm up with dynamic stretching as well as with static stretching. There was 51.15% increase in treadmill time to exhaustion in dynamic exercise protocol (PII), 29.63% in dynamic stretching protocol (PIII) and 18.72% in static stretching protocol (PI) when compared with control. These results are consistent with Koch et al  and Unick et al  which stated that there is short term improvement in performance after a bout of dynamic exercises compared with static stretching.
In their article Faigenbaum et al  suggested that it may be desirable for children to perform moderate to high intensity dynamic exercises prior to the performance of activities that require a high power output. According to Thompsen et al , warm up protocols that include dynamic exercise may be a viable method of enhancing jumping performance in athletic women as compared to stationary cycling and static stretching. It has been shown  that the performance on the vertical jump test would benefit from dynamic exercise warm up with weighted vest.
It has been reported  that compared with no warm up, there was a significant increase in treadmill time to exhaustion, when running was preceded by a 15 min warm up at either 60 or 70% of VO2max. In their article Burnley et al  concluded that priming exercise performed in the moderate and heavy intensity improved cycling performance by ~2-3% despite a mild lactacidosis being present at exercise onset. It has been concluded that dynamic warm up performed with a vest weighted with 2% of body weight may be the most effective warm up protocol for enhancing jumping performance in high school female athletes .
In their article Stewart et al  compared the effectiveness of warm up in relation to athletic performance. Preparation involving warm up resulted in significantly faster sprint times compared to preparations having no warm up. Warm up was effective at improving immediate sprint performance. It has been reported  that competitive and recreational athletes typically perform warm up activities to prepare for more strenuous exercise. These preliminary activities are used to enhance physical performance and to prevent sports-related injuries.
It has been determined by Gray and Nimmo  that there is influence of type of warm up on metabolism and performance during high intensity exercise. There is a significant increase in cycling performance when preceded by active warm up. Active warm up tends to result in slightly larger improvements in short term performance than those achieved by passive warm up alone.
Active warm up appears to improve both long term and intermediate performance if it allows the athlete to begin the subsequent task in a relatively non-fatigued state, but with elevated baseline oxygen consumption (VO2). While Bishop  discusses that active warm up improves endurance performance, it may have a detrimental effect on endurance if it causes a significant increase in thermoregulatory strain.
It has been stated  that there was impaired 2 min kayak ergometer performance if the subjects performed warm up at their anaerobic threshold, probably because of greater metabolic acidosis. Shellock and Prentice  discuss that dynamic stretching protocol shows increased time to exhaustion from static stretching protocol. A possible reason for this phenomenon may be the increase in core temperature during dynamic exercises in comparison to static stretching. Consequently, this may increase the sensitivity of nerve receptors and the speed of nerve impulses, encouraging muscle contractions to be more rapid and forceful.
Blood Lactate Concentration and VO2max
Dynamic exercise warm up protocol has been shown to have positive effects on blood lactate concentration and VO2max. There was decrease in lactate accumulation by 57.56% in dynamic exercise protocol (PII), 42% in dynamic stretching protocol (PIII) and 40.7% in static stretching protocol (PI) when compared with control. There was significant increase in VO2max by 14.26% in protocol PII, 5.66% in protocol III and 3.25% in protocol PI when compared with control. In their article Gerbino et al  found that blood lactate production during constant load, high intensity exercise was less when the O2 kinetics were speeded by prior exercise.
It has been concluded  that lactate production during submaximal exercise is O2 dependent. Muscle NADH decreases in low intensity exercises but increases during high intensity exercises. The increased NADH consistent with the accelerated lactate production during exercise is due to the limited availability of O2 in the contracting muscle. It has been demonstrated  that blood lactate accumulation and ventilation during graded exercise are dissociated.
The research documented a decrease in NADH with low intensity exercise at 40% VO2max and an increase in NADH with high intensity exercise at 75% and 100% VO2max. It suggests that the availability of O2 relative to the demand is decreased at high exercise intensities . It has been proposed  that the accelerated lactate production during submaximal exercise is due to limited availability of O2 in the contracting muscle.
Conclusions and practical application
The findings of this study can be summarized as follows: amongst three protocols: static stretching (PI), dynamic exercise protocol (PII), and dynamic stretching protocol (PIII), dynamic exercise protocol is the most effective in increasing aerobic power (VO2max), increasing endurance performance and decreasing blood lactate concentration. Thus, considering the above findings dynamic exercise protocol should be used in order to enhance endurance indices and possibly competition results in endurance sports activities.
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