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Abstract
Training loads contribute to sports injury risk but their mitigation has rarely been considered in a sports injury prevention framework. A key concept behind monitoring training loads for injury prevention is to screen for those at increased risk of injury so that workloads can be adjusted to minimise these risks. This review describes how advances in management of workload can be applied as a preventive measure. Primary prevention involves screening for preparticipation load risk factors, such as low training loads, prior to a training period or competition. Secondary prevention involves screening for workloads that are known to precede an injury developing so that modification can be undertaken to mitigate this risk. Tertiary prevention involves rehabilitation practices that include a graded return to training programme to reduce the risk of sustaining a subsequent injury. The association of training loads with injury incidence is now established. Prevention measures such as rule changes that affect the workload of an athlete are universal whereas those that address risk factors of an asymptomatic subgroup are more selective. Prevention measures, when implemented for asymptomatic individuals exhibiting possible injury risk factors, are indicated for an athlete at risk of developing a sports injury. Seven key indicated risks and associated prevention measures are proposed.
- Injury prevention
- Knowledge translation
- Sporting injuries
- Training
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Introduction
Injuries negatively affect the performance of athletes in sports teams1 and remaining injury-free has the potential to maximise athletic success.2 Therefore, injury prevention must feature in every high performance programme, to optimise performance. Recently, prevention in sports medicine has benefitted through learnings from broader prevention measures applied in population health. Chosen prevention can be based on targeting a specific pathology or injury (primary, secondary and tertiary prevention) or based on controlling injury risk factors (universal, selective and indicated prevention).3 This review is the first to place workload management within an injury prevention framework, and to demonstrate how load monitoring and management together should form a component of all prevention programmes for sports injuries in athletes.
Prevention based on a specific injury
Primary prevention
Primary prevention aims to prevent a specific injury through removal or reduction of its causal factors. Preseason screening, for example, aims to identify deficits in muscle flexibility, strength, balance or proprioception, joint range of motion and detailed history of previous injuries sustained. Preseason hamstring strength testing with the Nordic hamstring test4 followed by an eccentric strengthening programme for athletes with lower strength is one example of primary prevention.
Assessing prior training load history is critical. Conceptually, a lower ‘training base’ can result from a break in training or from chronically low workloads. Training bases can be assessed in simple or advanced ways. A study in junior elite football (soccer) players showed that athletes with a history of a low amount of training had higher rates of groin injuries after an intensive training programme.5 Training history was simply defined as the number of training sessions per week prior to start of the training programme. An increase from two to three sessions a week to daily or twice daily (as is common in these training programmes and club situations) poses a large risk of injury to the athlete. However, simple measures to control this risk are feasible.
High performance training camps also pose significant risks of injury. In judo, camp injury rates have been as high as 83%,6 and it has been suggested that these may be due to factors such as new techniques, higher intensity and scrutiny of coaching, or (micro) trauma from training. In this judo example, the average week-to-week increase in time (minutes of exposure) from the week prior to the camp was 469±246% (unpublished data). In this example, the risk of injury could be ameliorated by: (1) more training in the daily training environment prior to attending the camp; (2) less training at the camp; or (3) a combination of both such that prescription is individualised. Primary prevention may encompass all three of these methods.7
Secondary prevention
Secondary prevention aims to detect the injury of interest at a point early enough in its development where intervention can prevent its progression or worsening. Secondary prevention involves: (1) screening for early detection (ie, looking for subclinical forms of injury or known risk factors that may affect pathology); and (2) early intervention or treatment (adjusting the prescription of training loads to mitigate or reduce the effect). Screening of training loads does not screen for subclinical injury per se, but it is a surrogate of workloads known to initiate these (patho) biological responses to the load applied.
Secondary prevention is based on the principle of early intervention rather than removal of the risk factors. In elite cricket, prescribing the number of balls bowled in training is primary prevention. In contrast, where a cricket fast bowler has spiked in the amount of balls bowled due to a competition load (which is arguably uncontrollable), secondary prevention would involve adjustment of training loads during the subsequent 4 weeks to ensure that the effect of this ‘spike’ does not lead to injury. When prescribing training loads, biological timeframes and known mechanisms of injury must be considered. For example, in Australian football, high-speed running can be removed if an athlete is at risk of hamstring injury, as the majority of sprains occur during sprinting.8
Tertiary prevention
Tertiary prevention aims to reduce complications and any long-term burden of injury during treatment of the injury and rehabilitation, including subsequent injuries7 or prolonged absence from sport.9 ,10 As spikes in training loads can precede injury, rehabilitation should maintain training loads as much as possible to minimise loading spikes on return to play. This is important because failure to maintain sufficient training load is a risk factor for subsequent injury.11
Cross training that physiologically stresses the body without impacting on the injury's ability to heal may maintain some training loads.12 However, returning players to sport-specific sessions (typically achieved by increasing external loads such as running distance or number of pitches/overs bowled) still requires monitoring to avoid ill-advised spikes. Tertiary prevention could prescribe training loads that can be safely undertaken prior to returning to competition.11 Returning to either training or competition without graduated exposure to their physical demands may be responsible for recurrent and subsequent injuries.13
Typically, injured athletes have reduced training to 20%, 40% or 60% of normal in the first 3 weeks of rehabilitation. Assuming the training in the week prior to injury was at 100% of normal, their chronic training load (the average load over the past four weeks) for this period would be 55% of normal (chronic load=(100%+20%+40%+60%)/4). Should these athletes return to full training the next week (acute load=100%), then their acute:chronic workload ratio (ACWR) would be 1.8 and the week to week change in training load would be 30%. Recent papers set the approximate risks of (re)injury at 10% using the ACWR or 30% using the week-to-week change.13 ,14 Tertiary prevention therefore requires quantification of training and competition demands, and assurance that the athlete can achieve them before resuming full training and competition.
Prevention based on risk factors for developing a sports injury
Universal prevention
Universal injury prevention considers injury risk factors common to all (or most) sports, such as nutrition, physical activity, mental health, sleep and protective equipment use.3 Training loads are highly correlated with injury across sports15 and therefore can be considered a universal risk factor. Universal prevention measures can be illustrated through the ‘Pitch Smart’ programme,16 enforced in junior baseball in the USA. Daily pitch limits for each age group are applied to protect against load-related injuries to the shoulder and elbow. Mandatory rest periods, proportionate to the number of pitches, are enforced for each age group, to account for workload spikes.
Selective prevention
Selective prevention considers asymptomatic individuals displaying characteristics associated with injury risk factors (known as risk modifiers).3 These factors include age, sex, sport and training age (time training in a particular sport). Selective prevention programmes include neuromuscular training programmes targeting adolescents.17 Younger athletes will be injured sooner than their experienced team members, indicating that their workload tolerance is less.18 Athletes with low chronic training load have exhibited higher risk of injury compared to their peers.5 ,19 Rugby union players who have a low training history (approximately <4000 arbitrary units (AU)/month) and high-training history (approximately >8500 AU/month) are at more risk than those with a moderate history (approximately 5000–8500 AU/month).20 Understanding and accounting for training history is an important selective prevention measure.
Indicated (targeted) prevention
An athlete at higher risk of injury should be targeted for injury prevention.3 Average risk is determined by a range of selective and universal sports injury risk factors, including previous injury history. Routine monitoring and subsequent load management by support staff in elite sport is a form of targeted injury prevention. Recreational athletes can use monitoring apps for this prevention strategy. Seven evidence-informed principles are suggested:
Establish a moderate chronic load
A moderate level of training is protective against injury. In cricket, the threshold is >150 overs in a 3 month period19 whereas in rugby union a monthly training load between approximately 5000–8500 arbitrary units reduces the injury risk.20 Coupling small increases in training loads with a moderate chronic training load has been shown to be the safest combination in elite rugby league players.21 Importantly, when an athlete has established a moderate chronic training load, their ability to tolerate large fluctuations in week-to-week loads is reduced.21 Indicated prevention measures would include increasing or decreasing the workload to a moderate level for that sport.
High and low monthly training loads have both been shown to be associated with the same likelihood of injury, indicating a ‘U-shaped’ relationship.20 An athlete may require load management if there is an apparent reduced workload through injury, illness or programmed rest (holiday, bye week, postseason break). Decreased training in rugby players will result in a reduction of training loads and move an athlete from the protected group (approximately 5000–8000 AU) to the lower training group (<5000 AU). This will result in a doubling of the risk of injury, which is compounded on returning to training. Assuming a scenario where no training was undertaken for 2 weeks, an athlete's chronic load would now be halved. The athlete now has an injury risk of approximately 15% compared to baseline risk of 4%,13 and should undertake a prevention programme, that is, a graduated return to play.
Minimise the week-to-week changes
Spikes in training loads precede injury20 ,22 and an athlete is ‘at risk’ for up to 1 month after a spike.23 Modification to training loads prior to injury mitigates this increased risk and is a secondary prevention measure. Spikes in absolute load of approximately >1000–1250 AU over 1 week to the next have been shown to present increased injury risk in Australian football24 and rugby union.20 Week-to-week fluctuations greater than 1069 AU in rugby union resulted in a 60% increased risk of injury the following week.20 Weekly load changes of ≥15% also significantly increase injury risk, with a doubling of the previous week's workload resulting in an approximately 50% likelihood of injury in rugby league.14
Do not exceed the workload ceiling of safety for the sport
A ceiling effect is observed where accumulated training across a week or month is greater than a threshold that is associated with increased injury risk.8 ,20 ,24 Weekly internal loads >1750 AU or fortnightly internal loads >4000 AU have been associated with increased injury risk (weekly, OR=2.44; fortnightly, OR=4.74).24 External loads also have a ceiling of safety with 3-weekly total distance and sprint distance in Australian football.8
Ensure a minimum training load is maintained
Training at moderate workloads is protective.19 ,20 In football, some athletes have a relative under-loading of external loads prior to injury,25 as can be observed in fringe and non-selected players accumulating lower training volumes across a season.26 Equally, in cricket, fast bowlers who have an ACWR <0.50 display increased risk of injury compared to those with a higher ratio (ACWR, 0.5–0.99).22 In one study, low monthly training loads (<3684 AU) posed higher risks than did moderate training loads in rugby union.20 Increasing an athlete's monthly training load from a low to moderate zone would theoretically reduce their risk of injury in the following week by approximately 45%.20 Importantly, periodisation of training programmes may be associated with lighter weeks that move an athlete from the moderate (protected zone) to a low monthly training load.20 Careful load management needs to be taken after these lighter weeks to ensure that athletes do not increase their risk of injury when returning to higher loads.24
Avoid inconsistent ‘boom-bust’ workload patterns
Inconsistent loading patterns are more likely to result in injury such as tendinopathy.27 High-intensity training is a risk factor for overuse wrist injuries in young athletes,28 however, this may represent low chronic training loads coupled with bouts of high-intensity training.29 Indicated prevention would require consistent training loads be maintained until a moderate chronic load is established. The temptation for patient groups such as those with chronic tendinopathy is to avoid aggravating activities. However, on resumption of these activities, symptoms will generally return. So the advice should be to maintain physical capacity where possible so that the athlete can develop capacity to tolerate the ongoing demands of the sport.
Ensure training loads are proportionate to the workload demands of the sport
Congested fixtures increase both match injury incidence and severity,30 ,31 as well as the risk of injury in the subsequent match31 and month of training.23 Intensive, camp-based training has been associated with very high-injury incidence.6 In both situations, careful planning of the preceding training loads should occur to ensure that the shift in training loads is within the indicated risk prevention strategies.
Monitor the athlete throughout the latent period
The latent period of injury is the time between its biological onset and the time of first symptoms. In sports injury, a latent period has been reported up to 28 days.23 Where the athlete has spiked their training load,23 early intervention is required. These interventions may be a smaller week-to-week change20 ,24 or reducing the magnitude of the ACWR21 to minimise the risk in this period.
Conclusion
Measuring and managing training loads should be part of all primary, secondary and tertiary prevention programmes. Ideally, training load monitoring should be included in all primary and secondary prevention programmes to avoid the first injury or its clinical manifestation. Once an athlete is injured, load management is required as a part of the tertiary prevention programme. Load management has the potential to form a component of universal, selective and indicated prevention measures, with seven evidence-informed indicated prevention measures presented. Future studies describing injury prevention measures should report the prevention stage (primary, secondary or tertiary), and also encompass universal, selective and indicated approaches. Clinicians designing prevention programmes must undertake high-quality monitoring of injuries as well as training loads, to identify key selective and universal risk factors to inform the design individual level programmes of common pathologies in the sport.
Measuring exposure-adjusted risk factors for sports injuries is complex, as metrics of absolute exposure can over-estimate or under-estimate injury risk. Relative training loads22 may be more important to measure, as moderate training loads have been shown to be protective.19 Reporting of absolute risk is recommended to inform decision-making processes. In an injured athlete, the ability to increase training loads greatly is likely to be reduced. Future studies should evaluate the ability to change training loads in both injured and un-injured athletes.
What are the findings?
Load management is critical to primary, secondary and tertiary injury prevention.
Load management must also be a component of universal, selective and indicated prevention measures based on controlling and reducing the risk factors for the development of a sports injury.
Load monitoring, without concurrent management of training loads, is not sports injury prevention.
How might it impact on clinical practice in the future?
Training load management needs to be an important component of all programmes for the prevention and treatment of all sports injuries.
Seven evidence informed indicated sports injury prevention programmes can be applied in the field for anyone working with athletes.
References
Footnotes
Twitter Follow Michael Drew at @_mickdrew and Caroline Finch at @CarolineFinch
Funding MKD was supported by the Australian Institute of Sport. CFF was supported by a National Health and Medical Research Council (of Australia) Principal Research Fellowship (ID: 1058737). JC was supported by an National Health and Medical Research Council (of Australia) Practitioner Fellowship (ID:1048593). The Australian Collaboration for Research into Injury in Sport and its Prevention (ACRISP) is one of the International Research Centres for Prevention of Injury and Protection of Athlete Health supported by the IOC.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.