Exercise
11 Mar 2023
High-Intensity Training: benefits and potential injury risk — Part II
The literature describes several types of high-intensity training, the most prevalent being HIIT (High Intensity Interval Training). This is characterised by short blocks of vigorous, intense activity at around 90% of maximum aerobic power, followed by short periods of rest or low-intensity activity intended to allow recovery.
Another form of high-intensity training found in the literature is HIFT (High Intensity Functional Training), defined as a varied set of functional movements performed at high intensity (adjusted to the individual's capacities) with the aim of improving general physical capacities such as strength and cardiorespiratory capacity. CrossFit is a representative example of this type of training.
There are also references to HIRT (High Intensity Resistance Training), although we found no clear distinction in the literature between this and traditional low-volume, high-intensity strength training focused on the rate of force production. We did find one study with a high level of evidence and wide-ranging implications for the case in favour of high-intensity training, which used a HIRIT (High Intensity Resistance and Impact Training) protocol. We will cover that study in a future article on this site.
All these forms of training share one characteristic: high intensity. Is that characteristic associated with a greater incidence and prevalence of injury when high-intensity training is compared with other types of training?
It is worth noting that not all studies define what constitutes an injury in the same way, which can mean some injuries go uncounted and are therefore not associated with high-intensity training. If a given study counts an injury only as an acute musculoskeletal symptom that prevents the person from training for more than 24 hours, for instance, it will leave out chronic injuries which, although they may be associated with the type of training studied, do not stop the person training.
Given that CrossFit as a form of high-intensity training has been identified by some authors as one of the drivers of HIIT's popularity from 2013 onwards, and one of the reasons it has remained in the top five of the ACSM fitness trends list ever since, its injury potential is worth examining. In a 2021 systematic review, Rodríguez and colleagues identified an injury prevalence of 35.3%, with an incidence ratio of between 0.2 and 18.9 per 1,000 training hours. The shoulders, spine and knees were the areas most affected, and an average of 8.7% of injuries required surgery.
The authors note that the incidence ratio was similar to that found in football and rugby, and in weightlifting and powerlifting. As for the latter two, the result does not surprise us, since CrossFit makes use of many of the techniques of those disciplines. Of the 25 studies analysed in this review (two of which analysed the same data), only six reported the type of injury, identifying tendinopathies, joint injuries and muscle injuries as the most frequent. In all the other studies it is not clear what the authors considered to be an injury. It is worth noting that most injuries were associated with weightlifting movements, chiefly the squat, deadlift, snatch, clean and jerk and overhead press.
The level of evidence in this systematic review was not the highest, since of the 25 studies, 20 were cross-sectional and four were cohort studies, with no randomised controlled trials (RCTs) at all. It is also important to note that most of the studies analysed (20) collected information through self-completed questionnaires, which does not allow for a high level of evidence. The remaining studies collected injury-related information in hospitals or sports clinics.
References:
Rodríguez, M., García-Calleja, P., Terrados, N., Crespo, I., Del Valle, M., & Olmedillas, H. (2021). Injury in CrossFit®: A Systematic Review of Epidemiology and Risk Factors. Phys Sportsmed, 1-8. https://doi.org/10.1080/00913847.2020.1864675
…continued in Part III