• Mark Turnbull

How much is too much HIIT?


Previously I reviewed a recent study looking at the different muscle fibre typology of world-class cyclists in different disciplines. Now we need to understand how different muscle typology can affect recovery from high-intensity interval training to avoid over training.

It goes without saying, BMX and track sprinters were at one end of the spectrum with high proportions of fast-twitch muscles. Road climbers were at the opposite end with high slow-twitch composition.


There are some exceptions to the rule, every generation has a handful of athletes that seem to excel at multiple disciplines. However, world-level performance seems to select for a very race-specific type of athlete. You’ve have noticed this with your training partners, there's the sprinter, climber and ride all day endurance specialist. But beyond academic interest, how might our individual typology affect our training response?


Recovery From HIIT In the first of two companion studies from the same collaboration, the impact of muscle fibre typology on recovery from high-intensity interval training was explored (Lievens et al. 2020b - link at bottom of post). If a cyclist has higher proportion of fast-twitch fibres, which are capable of high force but fatigue rapidly, might it also mean that their recovery from a hard training session take longer than a cyclist with more slow-twitch fibres?

  • From a larger group of 32 initial participants, 10 trained cyclists with high FT typing and 10 with high ST typing were recruited.

  • Each group performed 3×30 s Wingate sprints. A single 30 s Wingate is tough. Rather than winding up to peak power, you start spun out at max power, then hang on for dear life. So 3 of these, done with 4 min rest, are just nasty.

  • Over the 5 h following this workout, each athlete performed repeated muscle testing. This included maximal isometric (leg stays in same position) knee extension. Isometric maximal force is also higher than when the joint moves. Also, muscle force from maximal electric stimulation was tested.

The expected results were seen from the Wingates themselves. The FT group had higher peak power during the first sprint. However, the rate of fatigue was faster in this group over both an individual Wingate sprint, and over the course of the three Wingates. Overall mean power output over the three Wingates were similar for both groups.


Importantly, the ST and FT groups were dramatically different in how they recovered over the course of 5 hours following this workout. In the ST group, there was a slight decrease in maximal knee extension torque at 10 min into recovery (~95% of baseline), but this recovered to pre-workout levels by 20 min.


In contrast, the FT group had a much greater torque reduction at 10 min (~75% of baseline), and torque was still significantly lower than pre-workout levels even 5 h into recovery.

Dosing Your Efforts I know from first hand experience that one of the biggest challenges for veteran athletes is the difficulty in recovering from hard efforts. While we can still smash out hard training, with age it takes us more days in between before we’re really ready for another hard effort.


The caveat with this study is that it only looked at the 5 h following a single workout, and testing wasn’t done in the days following. However, a study like this really highlights the importance, regardless of age, of individualising your recovery within your training. Besides age, it may be that sprinter types of athletes may also require more recovery between breakthrough workouts.


These types of athletes would also likely really benefit from a highly polarized training program, with the low-intensity training really giving the body the best chance of recovering in between breakthrough efforts. In contrast, ST athletes may be the ones who respond better to sustained threshold or sweetspot-type training due to their relatively faster recovery between efforts.


Determining Athlete Type Barring access to indirect or direct muscle fibre typing, how do you determine your athlete type? One way is using INSCYD performance testing, which determines the following data:

Maximum aerobic performance (VO2max)

Maximum glycolytic performance (VLamax)

Accumulation and recovery of lactate

Fat and Carbohydrate combustion rates

Aerobic v anaerobic energy contribution ratios

Anaerobic Threshold

Summary The main takeaway from this study is that the exact same workout can have drastically different impact on two riders because of their athlete types. Where this becomes especially important is that the same workout can cause much greater depth of acute and long-term fatigue in fast-twitch dominant riders, and this requirement for longer recovery must be accommodated within training.


Derived and based only on fundamental, peer reviewed basic science, INSCYD’s PPD is used by the highest ranked cyclists and triathletes around the world. Over the last few months, PPD has been beta tested by pro teams CCC Team, JUMBO-VISMA, Alpecin-Fenix, SEG Racing as well as by many World Tour coaches and coaching businesses. Testing and benchmarking has been done in direct comparison to lactate-and lab testing, ensuring top-level accuracy is guaranteed, AND validated.

Lievensetal.JAP2020
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