Sports medicine professionals – from those working with the general population through to elite sport practitioners are aware of the role of muscle weakness and poor neuromuscular control on injury risk. But the best practitioners are also aware that simply having poorly developed physical capacity is insufficient to cause injuries – these physical qualities interact with training load (and other variables) to either increase or decrease risk. For example, large spikes in training loads can increase fatigue, resulting in reduced eccentric strength and neuromuscular control, thereby increasing injury risk [13]. Conversely, gradually progressing to higher chronic training loads, can result in increased strength and aerobic capacity, which in turn, reduces injury risk [4].
An additional common theme with the majority of the load-injury research is that most have investigated these relationships in lower-body injuries. So, do the load-injury relationships hold true for sports involving upper-body actions (e.g. tennis, swimming, and throwing sports such as baseball, handball, and javelin)?
Spikes in Training Loads Increase Risk
Sharp increases in training load were associated with a 4.3-fold increased risk of shoulder injury in competitive swimmers [3], while spikes in competition, fitness training and/or training/competition workload increased the risk of shoulder injury in tennis players [7]. In the largest investigation on the influence of training load on shoulder injuries, Møller et al. [10] studied 679 handball players over a 31-week season. An increase in training load by >60% relative to the average of the previous 4 weeks was associated with a ~2-fold increase in injury risk (hazard ratio = 1.91). Similar findings have been observed in varsity-level baseball players – rapid increases in throwing loads (represented by an acute:chronic workload ratio >1.27) were associated with a ~15-fold greater injury risk than gradually progressed throwing loads [9] (Figure 1). These results are not a statistical artefact – consistent with findings from sports with a lower-body emphasis [4], spikes in upper-body training loads increase risk of upper-extremity injuries.
Why Do Some Athletes Tolerate Rapid Changes in Training Load, and Others Don’t?
It is well-documented that specific physical qualities moderate the relationship between training load and injury [13]. For example, in sports predominantly involving lower-body actions, lower-body strength has been shown to moderate the load-injury relationship – athletes with poorer lower-body strength have a higher risk of injury when exposed to a spike in training load [8] (Figure 2). Similar findings have been shown in throwing-based sports. In handball, players with poor shoulder external rotation strength (hazard ratio = 4.0) and scapular dyskinesis (hazard ratio = 4.8) were more likely to sustain a shoulder injury when exposed to rapid increases in training load [10] (Figure 3 & 4). Collectively, these findings demonstrate that well-developed upper-body strength and movement qualities may protect against injury when athletes are exposed to spikes in training load.
Does High Chronic Load Protect Against Upper-Extremity Injuries?
Gradually and progressively building to higher chronic loads is thought to promote resilience and reduce injury risk. However, studies describing the relationship between training load and lower-body injuries are equivocal – some have shown reduced injury risk with higher chronic training loads [6], while others have shown a “U”-shaped relationship whereby both low, and high chronic training loads increase risk [2].
Equally, similar findings have been observed for sports involving upper-body actions. For example, pitching >100 innings in a season is a risk factor for elbow injuries in youth baseball players [1]. Conversely, baseball players with high chronic training loads had better arm health (specifically shoulder mobility) than players with moderate or low chronic loads [11] (Figure 5).
How Can Sports Medicine Professionals Protect the Health and Performance of Athletes from Upper-Body Sports?
Although the majority of load-injury research has studied lower body injuries, the relationships between training load and injury largely hold true for sports with an upper-body emphasis (Figure 6).
So how can sports medicine professionals apply the research to protect the health of athletes from upper-body sports?
1. Monitor shoulder strength, scapular control and training load. Consider arm health when progressing upper-body loads and during periods of underloading.
2. Avoid spikes in training load, particularly in athletes with scapular dyskinesis and poor external rotational strength. Appropriately-dosed training load will provide the stimulus for the strength and neuromuscular control required to tolerate further training load.
3. Avoid excessive throwing volumes in-season and avoid shutting the arm down completely during off-season. Maintaining arm health through micro-dosed throwing loads and strength training in off-season, allows athletes to be better prepared to build to moderately-high chronic throwing loads in-season.
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References
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2. Cross MJ, Williams S, Trewartha G, Kemp SP, and Stokes KA. (2016). The influence of in-season training loads on injury risk in professional rugby union. International Journal of Sports Physiology and Performance, 11:350-355.
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11. Pexa B, Ryan ED, Blackburn T, Padua DA, Garrison JC, and Myers JB. (2020). Influence of baseball training load on clinical reach tests and grip strength in collegiate baseball players. Journal of Athletic Training, 55:984-993.
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