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.
Your arguments are the conventional wisdom, but do the statistics support this? Stretching was once thought to be a good way to reduce risk of injury. It was a big part of the conventional wisdom. It isn't that simple, however, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1250267/.
I think a good study would be to track people through something like their first 60 cumulative minutes of exercise after no exercise for, say, 6 months. If that 60 minutes happens in one hour or spread out over a week, is there any significant change in risk? If it is aggressive or gentle, is there any change in risk? This should be studied and verified. If it has, let me know.
I think we should treat all risks like the lottery or keno. Every time you play, your odds reset. This should be the conventional wisdom in all things.
This arguments are the ones used and shared by Olympic coaches. There is nothing new in what I say. It´s well known in sport circles that science goes between 10 and 20 years behind the Olympic training methods. They don´t have time to wait for studies to happen, they need to go for what it works now.
As I said HIIT is very very useful, possibly more effective than beginning as I said (depending of your objectives): developing slowly your capability over some months. But recommending it to people out of the blue, with out proper training time under their belt (doesn't have a minimum adaptation to physical activity) that don´t know how their own body reacts. It's just an injury waiting to happen. Not only that, Hiit training is so exhausting that a lot of people give up before they can see results. So one thing is to say that it´s effective, and other to say that it´s really useful or safe as it´s recommended, after all we are talking of finding a training system that it´s useful to the average guy who wants to start training.
IMHO it's much better to make a plan that makes you start slowly, with low volume and low intensity. And from there over the months (you don´t need a lot of them, 2-3 months is more than enough to develop a training base), start adding HIIT, etc.. But that's more difficult to sell, as we all want results this week.
What stretching does, is to allow a complete range of movement, for example people that perform bench press as their main exercise usually develop a strong forward tightness at their shoulder girdle (besides not stretching they usually don't balance the strength between pulling and pushing).
They are terribly strong in one movement (pushing), but this tightness and lack of balance helps develop a lot of shoulder problems overtime, and even it can stop the body from further developing the bench press strength. It´s more complex than only stretching. But stretching has it´s place, you only need to look at Gymnasts and Weight lifters, that are the most powerful athletes gram per gram (of relative strength, not absolute like power lifting). Both of them are very very flexible compared to the average sport practitioner. They develop that stretching capability because they need it to perform well. At that level you don't train a property that you don't need.
Of course circus levels of flexibility are way too much and could lead to problems.
But they are certainly specially dangerous with certain kinds of HIIT as you are performing very close to your maximum capability. At this point the body is under maximum stress and it´s necessary to warmup for a minimum of 10-20 min to perform it with some safety.
-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.