European Journal of Cardiovascular Medicine

A game of football could be represented as an exercise protocol of running about 150 meters every minute for 90 minutes, with a 15-minute rest period after the first 45 minutes. A high demand is placed on the player’s aerobic capacity to achieve this(1). It is well documented that there is a significant relationship between aerobic capacity i.e. VO2max and the total distance covered, frequency of sprints made in a match, as well as the number of involvements with the ball by football players(2). Soccer includes high intensity, intermittent bouts of exercise, which stresses the anaerobic glycolysis metabolic pathway. The high intensity burst of football is fueled by anaerobic glycolytic system(3).

Aims & objective:

Primary: To determine VO2 max values and plasma lactate values in football players undergoing continuous training and HIIT (high intensity interval training).

Secondary: To assess the effect of continuous training and interval training on VO2max and the plasma lactate values of football players and statistically compare them.

The approval of the study protocol was obtained from the institutional Ethics committee. Sixty football players were included in the study as per selection criteria.

Inclusion criteria:

1. Professional football players who play regularly and have participated in club level football games for more than five years.
2. Male football players in the age group of 18 to 25 years were enrolled.
3. Written consent of the subjects was taken for the study.

Exclusion criteria:

1. Subjects having symptoms of cardiopulmonary disease, or history of any chronic disease.
2. History of smoking.
3. History of injury.

60 football players were randomly allocated into two groups i.e. 30 players in continuous training group and 30 players in interval training group for 6 weeks training.

Continuous training:

An effort of 60 minutes jogging daily for 5 days in a week.

Interval training: (Little method)(4).

A regimen based on a 2009 study uses 60 seconds of intense exercise followed by 75 seconds of rest, repeated for 10 cycles. Subjects using this method were trained 3 times per week.

Basic data collection: The subjects of the two groups were measured for weight, height and BMI were calculated.

Outcome measures: VO2max and plasma lactate values were taken one day prior to the beginning of training and two days after completion of 6 weeks of training.

Procedure:

Determination of VO2max:

Queen’s college step test was used to predict VO2max. Subjects were asked to come 3 hours after a meal without indulging in any vigorous exercise within the prior 24 hours. After doing prior warm up for 5-6 minutes, subjects were asked to step up and step down on a 16-inch wooden bench. The subjects were asked to do each stepping cycle to a 4-step cadence, up up and down down continuously for 3 minutes. The stepping cycle was monitored with the help of a metronome. After completion of the test a 15 second recovery heart rate was measured. It was converted to bpm by multiplying by 4.

Following equation was used to calculate the VO2max:(5)

VO2max (ml/kg/min) = 111.33 – (0.42 x step test pulse rate in beats per minute)

Estimation of plasma lactate:

Subjects were asked to come 3 hours after a meal without indulging in any vigorous exercise within the prior 24 hours. They were asked to perform an all-out effort of running for 60 seconds. Immediately after this, under aseptic precautions, 2 ml of venous blood sample was taken in a Gray Top sodium fluoride vacutainer. Plasma was separated from the cellular components within 15 minutes of collection. Samples were packed into plastic vials containing ice packs. These samples in the lab were analyzed by spectrophotometry. The results were expressed in (mg/dl). By this method the normal resting plasma lactate level is 4.8 – 19.8 mg/dl.

Statistical analysis:

The statistical analysis was done using GRAPHPAD PRISM 5 software.

The Mean, Standard Deviation of all the baseline characteristics and the parameters i.e. VO2 max and plasma lactate values were calculated. Unpaired and paired t test was used to compare baseline characteristics and parameters respectively. The p value less than 0.05 and less than 0.01 were considered significant and highly significant respectively

In the present study, VO2 max and plasma lactate values in continuous training group and HIIT group were estimated and compared.

1. Total n=60 subjects, 30 in continuous training group and 30 in HIIT group were included.
2. The mean value for age, body weight, height, and body mass index in continuous and HIIT group were 20.36 ± 2.23 years, 61.7 ± 4.54 kg, 170.9 ± 4.69 cm, 21.15 ± 1.33 kg/m² and 20.96 ± 2 years, 61.86 ± 4.56 kg, 171.96 ± 4.49 cm, 20.79 ± 1.70 kg/m² (Table 1)
3. The mean value of VO2 max before and after training in continuous training group was 46.43 ± 3.70 ml/kg/min and 50.79 ± 3 ml/kg/min respectively. This was statistically highly significant p value < 0.0001.(Table 2, graph 1)
4. The mean value of VO2 max before and after training in HIIT group was 47.03 ± 3.45 ml/kg/min and 60.31 ± 2.80 ml/kg/min respectively. This was statistically highly significant p value < 0.0001.(Table 3, graph 1)
5. The increase in mean values of VO2 max in continuous training group i.e. 4.34 ± 2.39 ml/kg/min and in HIIT group i.e. 13.27 ± 2.49 ml/kg/min respectively when compared was found to be statistically highly significant p value < 0.001.(Table 4, graph 2)
6. The mean plasma lactate values before and after training in continuous training group were 32.01 ± 6.99 mg/dl and 64.68 ± 7.28 mg/dl respectively. This was statistically highly significant p value < 0.0001.(Table 5)
7. The mean plasma lactate values before and after training in HIIT group were 34.32 ± 7.47 mg/dl and 100.20 ± 8.66 mg/dl respectively. This was statistically highly significant p value < 0.0001.(Table 6, graph 3)

The increase in mean values of plasma lactate in mg/dl in continuous training group i.e. 33.32 ± 8.43 mg/dl and in HIIT group i.e. 65.87 ± 7.11 mg/dl respectively when compared was found to be statistically highly significant p value < 0.001.(Table 7, graph 4)

Table 1 Baseline characteristics of the study group

Table 2 Mean VO2 max values before and after training in continuous training group.

Table 3 Mean VO2 max values before and after training in HIIT group.

Table 4 Comparison of increase in mean VO2 max values between study groups  

Table 5 Mean plasma lactate values before and after training in continuous training group.

Table 6 Mean plasma lactate values before and after training in HIIT group.

Table 7 Comparison of increase in mean plasma lactate values between study groups

** statistically highly significant, CT continuous training, HIIT high intensity interval training, SD standard deviation.

Multiple mechanisms can explain these changes due to training interventions like continuous training and HIIT on cellular and central level(6).

Training significantly increases capillary density and mitochondrial size. The concentration of enzymes and transfer agents involved in aerobic metabolism also increases two to three-fold, enhancing the capacity to generate ATP aerobically, particularly via fatty acid breakdown(3).

One potential mechanism of increase in aerobic power is an increase in the oxidative capacity of muscle fibers(7). HIIT results in increased levels of muscle Na+/H+ exchanger isoform 1 (NHE1) and Na+K+ pump alpha 1 subunit. This causes lower K+ accumulation preserving excitability and lowering fatigue(8). Increased left ventricular ejection fraction as well as increased contractile efficiency of heart muscle fibers also explain improvement surrounding HIIT training. Increased expression of PGC -1 α gene in muscle fibers after HIIT training for 6 weeks that causes increased activity of mitogen activate protein kinase and calcium signaling mechanisms also explains the results obtained. Lactate accumulates when anaerobic energy transfer predominates. Lacmax (maximum lactate) increases significantly after HIIT and on the other hand has been shown to decrease after continuous training(9). Lower catecholamine levels during submaximal exercise decrease the lactate production due to decreased glycogenolysis(10). Also lactate clearance is more in submaximal exercise(11).

Gormley et al. (2008)(12). showed that when volume of exercise is controlled, higher intensity improves VO2 max more than lower intensities.

G Sporis, L Ruzic, G Leko (2008)(13). studied and found that anaerobic endurance of elite soccer players improved after a high intensity training intervention in an 8-week conditioning program.

There was marked improvement in VO2 max and plasma lactate in both continuous training and HIIT group and it was comparatively more in HIIT group. Thus, HIIT group showed superior aerobic and anaerobic capacity. HIIT is indeed a time efficient strategy to induce rapid muscle and performance adaptations compared to traditional continuous training. A comprehensive evaluation of physiological adaptations induced by different interval training strategies in a wide range of diseased and healthy populations will ultimately permit evidence-based recommendations that may provide an alternative to current exercise prescriptions for time challenged individuals.

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