Aerobic capacity, cardiorespiratory endurance, is directly related to the ability to produce physical work and is important for the health and quality of life of every human being. Maximum oxygen uptake (VO2 max) is the most reliable indicator of cardiorespiratory endurance. Many factors influence maximal oxygen uptake, including training approach, age , gender, heredity, and body composition.

Interval training alternates efforts of intense physical work with recovery intervals.   Active or passive. The shorter time required to achieve the desired physiological adaptations makes it particularly attractive as a training option.

In the continuous training method, as its name suggests, we have continuous effort without the interference of a break. This occurs at a moderate intensity of effort, which can still produce the desired physiological adaptations.

It has been to date, and remains an important training option, as it is to some extent associated with increased training volume, which, when increased in a controlled manner, increases the desired physiological adaptations and performance. It plays a particularly important role in sports in which cardiorespiratory endurance and peripheral adaptations are crucial.

Various training methods have been proposed and used to improve VO2max, which bring about the desired results. In this review we will try to demonstrate whether continuous moderate intensity training and intense, predominantly interval training are effective and identify any differences in effectiveness between them. Both training approaches appear to be effective in improving VO2max peak oxygen uptake. Intense, interval training, is definitely more effective if training time is equated and seems to be probably also more effective when anticipatory work is equated. In this case, training mileage. However, because the two different workouts induce partly different physiological adaptations, it is appropriate to use both in training in order to achieve the maximum possible improvement in VO2max

Many scientific papers have shown that adaptations to high intensity training are similar to the continuous method and in some cases superior to it.  Research has shown that four 4-minute running repetitions at 90-95% of maximum heart rate  (HRmax) followed by 3 minutes of active recovery at  70% HRmax when performed 3 times per week for 8 weeks  produced a 10% greater improvement in stroke volume when compared to long slow running. In addition other research demonstrated that high-intensity aerobic exercise at  90-95% of maximal oxygen uptake (VO2max) caused a 12% increase in left ventricular mass and a 13% increase in cardiac contractility. This event is directly comparable to cardiovascular changes observed in continuous aerobic training. Some researchers suggest that improvements in VO2max induced by high-intensity interval training (HIIT) are superior to those induced by the continuous method. In addition, improvement in cardiovascular function, and an increase in VO2max are the main goals for patients suffering from cardiovascular diseases. For this reason, some cardiovascular rehabilitation centers are beginning to include interval training for their patients… The results show similar improvement to low-intensity, long-duration training, but in a shorter period of time and with a shorter training frequency. 

Following is a review article

Chronic responses to peak oxygen uptake VO₂max  in continuous moderate-intensity and high-intensity training.

                                                                         TZANETAKIS IOANNIS  Msc Exercise Physiology and Training Science

                                                                                                       INDIVIDUAL LITERATURE REVIEW

Chronic responses to peak oxygen uptake VO₂max  in continuous moderate-intensity and high-intensity training.

1.Introduction

Aerobic capacity, cardiorespiratory endurance, is directly related to the ability to produce physical work and is important for the health and quality of life of every human being (9,10). Maximum oxygen uptake VO2 max is the most reliable indicator of cardiorespiratory endurance (11). Many factors influence maximal oxygen uptake, such as training approach, age , gender, heredity, and body composition.

Interval training alternates efforts of intense physical work with recovery intervals.   Active or passive. The shorter time required to achieve the desired physiological adaptations makes it particularly attractive as a training option.

In the continuous training method, as its name suggests, we have a continuous effort without the interference of a break in a moderate intensity effort, which can still produce the desired physiological adaptations. It has been, and remains, an important training option as it is to some extent associated with increased training volume, which when increased in a controlled manner, increases the desired physiological adaptations and performance, particularly in sports in which cardiorespiratory endurance and peripheral adaptations play the most important role.

Various training methods have been proposed and used to improve VO2max, which bring about the desired results. In this review we will try to demonstrate whether continuous moderate intensity training and intense, predominantly interval training are effective and identify any differences in effectiveness between them.

In the research by Yunus M , Wahjuni E , Supriatna  2018 there appear to be many significant deficiencies. First, the training units are not described. Nor the running intensity , either as a percentage of VO2max, Vvo2max, heart rate or some other benchmarking- comparison measure. Also in the intervals no recovery duration is mentioned. Only the weekly frequency and the total duration of the training intervention are reported. Not even the duration of the training sessions The equipment used to carry out the tests is not mentioned and the method is vague and it is not made clear whether it was evaluated by spirometry

In the study by Lars Nybo et al. 2010 while specifying the total daily training time (20min for the interval training group (IDT), the warm-up time (5min) , as well as the intensities (5min X2) is not mentioned whether the remaining time of 5 min was distributed between the running intensities and in what way. Regarding the IND group, although 2 of the 3 workouts were performed each week, nevertheless the increase in VO₂max was almost double that of the other groups.

In the study by Frédéric N. Daussin  et al. 2008  a clear difference in VO2max improvement in favour of the interval method was shown, although the duration during which the exercisers cycled at high intensity was minimal and the ratio of intervals not the most suitable.

In the study by Catia Martins et al. 2016 while there were no statistically significant differences in VO2 max between groups , it is interesting that intense interval training with only half the effort task produced a similar improvement in VO2max.

In Efrain James Sanchez’s 2013 postgraduate thesis the HIIT group was coached , supervised, motivated, while the CET was trained individually. This may be a major limitation of the research. Estimating VO2 max with the 12 min Cooper Run test although it has a correlation (.90) with respect to ergospirometry measurements, it is certainly not the most effective way of estimating VO2max. It also did not equate training sessions in terms of training volume (total weekly kilometers, or effort time) either

In the study by Kuno Hottenrott , Sebastian Ludyga  and Stephan Schulze 2012 the change – improvement in body composition might not be due to the training interventions, but to the dietary choices of the trainees, as these were not monitored. Aerobic power was only measured in a test of increasing intensity increments on the floor ergometer. The results cannot be generalised to other types of running tests, as demonstrated by the fact that there was no difference in half-marathon performance. The effect of the training variables (intensity and frequency) cannot be evaluated independently as the study compares equalized total time of training intervention.

In the study by  Saba Khan, Razia Nagarwala, Ashok Shyam, Parag Sancheti 2019 the determination of VO2max using the adapted  Bruce protocol falls short of gas exchange spirometry in accuracy.

In the study by  Gordon Fisher et al. 2015 the total high-intensity time for exercisers in the HIIT protocol was minimal to cause significant changes in VO2max. Also the weekly frequency and total training volume were significantly greater in the MIT group. So it would be unlikely from the outset that the HITT group would show greater adjustments in VO2max