There are several problems with this kind of studies:

-Almost all kind of exercise will improve all markers in sedentary, not trained people.

-We all look for miracle solutions, but if you really want to improve it´ll take some time and long term commitment.

-Interval training works, but it´s currently sold as the solution for all the fitness problem. It has it´s own problems dough. Some of this problems are:

+Lack of proper warm up (Higher risk of injury)

+Lack of proper progression (just go and run), it's a dangerous way to stress an untrained cardiovascular system and muscular, esqueletical and connective tissues. They may not be able to manage the sudden stress and something may break.

+Lack of technique, running at slow speed is not that demanding, but an all-out sprint will increase the probability of an injury due to improper movement.

+Overtraing. Not even Olympic level athletes train all out all the time, the body needs recovery to improve. You give it some stress (not too much, just the least stress necessary) and then leave it to recover, It´s called overcompensation. If you are not training to obtain this overcompensation you are just wasting your time (or amusing yourself with a very high heart rate)

The biggest problem with all this fitness trends is that they oversimplify. Steady state low heart rate training has it´s place (creating an aerobic base level, improving technique, improving movement economy, recovery), as interval training does (pushing the anaerobic limit, increasing the VOmax, increasing the work capacity at max aerobic levels). Cardiovascular training is a continuum and isolating it´s parts leads to partial results.

To really be effective, they must be used inside a complete program, with volume and intensity progression, to allow the body to adapt progressively to the stress. With recovery periods (weekly monthly and yearly) to allow the body to recover and overcompensate (most interval training systems out there forget to tell people how to recover)

This may seem like loosing your time, after all people think that if you push yourself everyday you´ll end being the strongest, and the fastest. But this only leads fast to over training and injury.

The best a sedentary person can do is to look for a coach that´s able to create a long term plan adapted to her needs and goals. The plan needs to take care of aerobic-anaerobic progression (with the intervals at it's due time), muscular mass with proper care of balancing muscular groups (better muscular mass correlates to better long term health, balanced muscular groups greatly diminish the risk of injury), technique (if needed for the sport), mobility and stretching (if you are tight it´s easier to develop imbalances and to get an injury).

It´s complicated, and the knowledge needed to create a good training plan that adapts over time, takes much longer than a weekend certification course.

You don´t need a lot of time a week, 3 hours a week can take you very far. If you don´t have time for 3 hours/week to work out it´s better to start thinking in your priorities.

And for those who lack the resources for a coach (as it´s my case) there are out there very comprehensive and well thought standard training programs for different sports, put together by professional and national level Coaches in form of books, apps and web sites.

Edit: Paragraph arrangement.