For this journal club we are going to be looking at the following paper:
The research focuses on reduced preseason training loads and whether they are associated with reduced injury incidence. It has been chosen by Tim Lathlean who is studying a PhD in Accredited Exercise Physiology at Monash University in Australia.
What was the aim of the paper?
Preseason training has been demonstrated as of great importance for both improving player performance as well as player resilience to injury. Preseason training loads that are excessive may lead to prolonged fatigue and overtraining syndrome, with athletes at greater risk of illness and injury. Previous studies have reported the pre-season incidence of injury of 116.1 per 1000 training hours as 2.6-fold higher than the seasonal average injury rate (45.3 per 1000) (Gabbett 2001). Moreover, increases in training loads are significantly correlated (r = 0.86) with increases in training injury rates (Gabbett 2004).
The purpose of the present study was to investigate if reductions in pre-season training loads reduced the incidence of training injuries in rugby league players. In addition, a secondary purpose of this study was to determine if the reductions in training loads compromised the improvements in physical fitness obtained during the pre-season preparation period.
What did the study involve?
Two hundred and twenty sub-elite Australian rugby league players registered with the same club participated in the 3-year prospective cohort study (2001 to 2003). Seventy nine players participated in the 2001 season, sixty five in the 2002 season and 76 in the 2003 season. Eleven players participated in two or more seasons.
In order to assess fitness adaptations from preseason training players completed testing for muscular power (vertical jump), speed (10m, 20m and 40m sprint), maximal aerobic power (multi-stage fitness test). Players participated in 30 pre-season training sessions each year with training loads decreased by training duration in 2002 and training intensity in 2003.
Training intensity was measured by using a modified rating of perceived exertion (RPE) scale, which was multiplied by training duration to calculate overall training load. Injury was defined as ‘any pain or disability suffered by a player during a training session’ and severity was classified as transient (no training missed), minor (one training week missed), moderate (two to four training sessions missed), or major (five or more training weeks missed).
Injury exposure was calculated by multiplying the number of players that participated by the session duration. Injury rates were calculated by dividing the total number of new injuries by the overall training injury exposure.
What were the main results?
The training intensity in the 2003 pre-season was significantly lower (p<0.01) than the 2001 pre-season. There were no significant differences between the 2001 pre-season (4.20 units, 95% CI: 4.09 to 4.32) and the 2002 pre-season (4.05 units, 95% CI: 3.89 to 4.22) or the 2002 pre-season and the 2003 pre-season (3.90 units, 95% CI: 3.75 to 4.05) for training intensity. Training duration was significantly higher (p<0.001) in the 2001 pre-season (78.1 min, 95% CI: 77.1 to 79.1) than the 2002 pre-season (67.9 min, 95% CI: 66.8 to 68.9) and 2003 pre-season (74.5 min, 95% CI: 73.7 to 75.3) period. The 2002 and 2003 pre-season training loads were significantly lower (p<0.001) than the 2001 pre-season training loads. There were no significant differences (p>0.05) between the 2002 and 2003 pre-season training loads.
The overall injury exposure for the three pre-season periods was 1442.4 (2001), 1165.9 (2002), and 1478.9 (2003) training hours at risk. The incidence of injury was significantly higher (χ2 = 44.3, df 2, p<0.001) in the 2001 pre-season period (156.7 per 1000 training hours, 95% CI: 136.3 to 177.1) than the 2002 (94.4 per 1000 training hours, 95% CI: 76.7 to 112.0) and 2003 (78.4 per 1000 training hours, 95% CI: 64.2 to 92.7) pre-season periods.
The majority of injuries sustained over the three seasons were to the lower limb, with the incidence of thigh and calf (χ2 = 14.6, df 2, p<0.001) as well as ankle and foot injuries (χ2 = 26.9, df 2, p<0.001) being significantly higher in 2001 than 2002 and 2003 preseason periods. The incidence of muscular strains (χ2 = 44.6, df 2, p<0.001), joint sprains (χ2 = 17.0, df 2, p<0.001), and haematomas (χ2 = 7.1, df 2, p<0.05) was significantly higher in the 2001 pre-season period than the 2002 and 2003 pre-season periods. Overexertion (χ2 = 38.2, df 2, p<0.001) and overuse (χ2 = 11.1, df 2, p<0.01) injuries were more common in the 2001 pre-season period than the 2002 and 2003 pre-season periods.
In terms of physical fitness capabilities, whilst aerobic power was similar across the three years, speed measurements were significantly faster (p<0.05) in the 2003 pre-season. Further, there were greater improvements in muscular power in the 2003 preseason period, with a 76% probability that the improvements were of physiological significance.
What can we take from this research paper?
This paper identified the issue of managing training loads effectively as an evidence based injury prevention program over the preseason period. Whilst it is important to have sufficient load for fitness adaptations, excessive load may lead to increased risk of injury. The present paper demonstrated that reducing training loads by duration (2002) and intensity (2003), reduced injury rates without compromising physiological capabilities. A 10.6–15.7% reduction in training loads reduced the incidence of injury by 39.8–50.0%, without compromising the pre-season improvements in physical fitness. Indeed, there was a greater relative change in V˙o2max with reduced training loads (2001, 7.7%; 2002, 11.8%; 2003, 15.6%).Further, there were greater improvements in speed and power over the 2003 season.
Subsequent sporting injuries can be explained by several risk factors including age, previous injury and playing experience. These may have contributed to the increased injury incidence of the older playing group in the 2001 season; however, these athletes also appeared in be in a state of overtraining. In their case, the training loads applied, in conjunction with inadequate recovery, were greater than was tolerable for their musculoskeletal systems.
The present paper demonstrates injury prevention to be of great importance in optimising physiological and fitness capabilities for performance in sub-elite sport. Further, a sub-elite athlete undertaking a progressively overloaded training program, performing two sessions per week, may expect a 7.5 to 15.9% increase in aerobic fitness, and stable 10m, 20m and 40 m speed. In addition, the 2003 season 5.7% improvement in vertical jump provides evidence for physiologically significant improvements in muscular power.
Practical applications from this study?
The physiological improvements made by reducing training loads in this study do not equate with recorded win-loss records. As such, further research incorporating training load monitoring, physical fitness assessment and the injury surveillance needs to be linked with individual player and team performance. This work provides great potential for investigating appropriate preseason training loads in sub-elite sport. Further investigations are required in team sports other than rugby league as well as the elite junior and senior competition levels.
Gabbett TJ. Severity and cost of injuries in amateur rugby league: a case study. J Sports Sci2001;19:341–7.
Gabbett TJ. Influence of training and match intensity on injuries in rugby league. J Sports Sci2004;22:409–17.