Endurance sport is one of the greatest tests of mental and physical toughness. During a marathon an athlete, on average, will complete 160-200 steps per minute. Whilst running has numerous benefits for our health and wellbeing, it can be monotonous loading on the skeletal system. Bony stress injuries account for up to 20% of running related injuries per year. It is believed that one reason for this is the repetitive overloading on runners’ bones. In comparison, activities involving irregular movements seem to foster greater bone health. The ultimate goal should always be injury prevention, so, should runners incorporate directional movements into their training repertoire for bone health?

Bone is an alive, adaptable, and dynamic structure. Our bone density increases as we grow and by 30 our density is at its peak. After this age we can only maintain what we have. Bone health refers to our bones’ mineral density and quality and is the result of a plethora of factors. In otherwise healthy runners, energy availability, biomechanics, training load and recovery, all play important roles in creating good bone health. Poor bone health can increase the risk of fractures during one’s developmental years and later in life.

There are two main theories that address the way in which our bones are loaded during running. The muscle-bone unit theory refers to the pulling forces created by a muscular contraction. The other references the ground reaction forces through bone when the foot contacts the ground, producing torsional and compressive load. Both mechanisms create macro-trauma which stimulates tissue production and shapes bones geometric structure. However, like other tissues in the body, the activity needs to be progressive otherwise the bone may become accustom and stop adapting. These principles may be used to help runners who may otherwise be stunting adaptation through habitual running load.

In general runners’ bones are healthier than sedentary people. Unfortunately, runners consistently demonstrate lower bone mineral density (BMD) when compared to matched individuals who partake in high impact and irregular movement based sports. A summary of the research of athletes (aged 14-30) found soccer, basketball and volleyball players as well as gymnasts, all displayed greater BMD than those who only ran. A study of young soccer players demonstrated that female players had healthier tibiae than runners and both genders had better density at the spine, femur and calcaneus. In separate studies of track athletes and infantry recruits those who also regularly participated in basketball had up to an 82% reduction in stress fracture risk. Interestingly, in masters athletes those who participated in sprinting had greater BMD than their peers who competed in long distance running. The benefits of diverse loading in youth were also found to protect runners later in life with some up to 50% less likely to sustain a stress fracture.

What seems to be more unclear is the ideal dosage for bony loading. Bone regeneration cycles are suggested to take 3-8months. Studies of humans, mice and turkeys found significant changes after as little as 3 weeks of a jump program. Repetition amount also widely varied between studies from 30 - 350 cycles per week. A study of adolescent females found that a 9-month plyometric program improved only greater trochanter bone strength. Another found plyometric training only benefited those who participated in low osteogenic sports such as swimming. Studies on structure found that rate, magnitude and activity resulted in site specific changes, however, no optimal values for load were presented. No well-known study was found to investigate an irregular, directional and high impact, loading program for the reduction of fracture risk in endurance runners.

It is important to note there are many other factors which influence bone health that have not been explored here. The body needs a plentiful supply of vitamin D and Calcium to build strong bone. To create an optimal environment for this rest and good sleep are also essential. For distance runners who are constantly in a state of low energy availability, bone loading has been found to have little strengthening effects and can be somewhat detrimental if added in addition to their normal training.

Runners want to run. Convincing them to do otherwise continues to remain a great challenge for clinicians, however, it would seem that some variety may strengthen their bones. Youth runners should be encouraged to participate in a variety of sports. Once specialisation occurs, a runner may benefit from incorporating direction and plyometric loading into their training. Unfortunately, the optimal dosage for this is largely unknown.

References
Beck, B. R., Daly, R. M., Singh, M. A. F., & Taaffe, D. R. (2017). Exercise and Sports Science Australia (ESSA) position statement on exercise prescription for the prevention and management of osteoporosis. Journal of Science and Medicine in Sport, 20(5), 438-445.
Gómez Bruton, A., Matute-Llorente, Á., González-Agüero, A., Casajus, J., & Vicente-Rodríguez, G. (2017). Plyometric exercise and bone health in children and adolescents: a systematic review.
Gómez-Cabello, A., Ara, I., González-Agüero, A., Casajús, J. A., & Vicente-Rodríguez, G. (2012). Effects of training on bone mass in older adults: a systematic review. Sports Med, 42(4), 301-325.
Hart, N. H., Nimphius, S., Rantalainen, T., Ireland, A., Siafarikas, A., & Newton, R. U. (2017). Mechanical basis of bone strength: influence of bone material, bone structure and muscle action. Journal of musculoskeletal & neuronal interactions, 17(3), 114-139.
Hong, A. R., & Kim, S. W. (2018). Effects of Resistance Exercise on Bone Health. Endocrinology and metabolism (Seoul, Korea), 33(4), 435-444. doi:10.3803/EnM.2018.33.4.435
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Despite the large amount of knowledge we now have regarding injury prevention of athletes, the shear amount of non-contact injuries that occur each year can be alarming. The balancing act between allowing an athlete to perform at an elite level and keeping them in a rehabilitation program for an extra couple of days can be a decision that keeps the medical team up at night. There are many factors which can contribute to a decision such as this and being pain free is not always a necessity. It has been found that an athlete’s performance will increase with volume and intensity increases, however, with these factors also comes the increased risk of injury. It has been found that an athlete is seventy times more likely to suffer injury if they exceed their individual weekly training threshold. The following article looks to answer some questions in how the medical team may deal with the manipulation and interpretation of an athlete’s load during the during pre, inter and post season.

Pre-season training for elite clubs, is the strength and conditioning programs designed to prepare athletes for an entire competitive season and not just an individual event. For amateur clubs the pre-season may be used for maintenance of fitness in the post season. The development of a well-planned pre-season training program can lead to a decrease in injury risk, increase in mental strength and condition the body for the cues and contacts of a game. The old adage of “train smarter not harder” has changed with the recent evidence produced by Tim Gabbett and Peter Blanch, with the new spin stating: “Train Smarter, Train Hard”.

The premise being that completing short hard training sessions is more beneficial to athletes than those of a longer duration which has the potential to increase injury risk. Training hard with a vehicle like High Speed Running helps to protect physical qualities of an athlete. However, a well-planned pre-season can only be as well planned as the measurement of the athletes load during that pre-season.

Measuring Loads

There are a number of different ways that load can be measured both subjectively and objectively and all with their own pros and cons.

One such way of measuring an athletes training load is through the use of the Acute: Chronic Workload Ratio. The chronic workload is measured over a four week rolling average, while an acute workload can be anything from one training session to one week, depending on the fatigue level of the athlete. The ratio known as the “sweet spot” is between 0.8 and 1.3, this is further supported by the rule of “10% volume increase” which would produce a 1.1. The “Danger Zone” in the Acute: Chronic Ratio is any workload exceeding 1.5, however, there is increased risk for any ratio above a 1.

Another way of measuring athlete load is through Rate of Perceived Exhaustion (RPE) times the duration of the session (minutes). Using this measurement tool allows for not only physical load to be recognized but the mental load being placed on an athlete. If a programmed session is expected to rate a 7 on the RPE scale but the athlete scores the session as 12 then there may be something else worth exploring within the athletes life.
It is suggested that you have 7 days to manage an injury risk for a non-contact presentation. If an athlete is seen to be in the danger zone for too long a period the use of more recovery sessions or complete rest may be required to decrease the physical and mental stressors affecting the athlete. The load variables that have potential to affect the load felt by the athlete are sport specific and can be both intrinsic and extrinsic in nature.

Contributors to Load

There are a large number of factors which can contribute to load accumulation in an athlete and how that load accumulation is attenuated by the tissues of the body. Past injuries are one of the biggest contributors to future injury whether within the same region of tissues or in a separate region as a result of detraining. What was originally an ankle injury which saw an athlete reduce training load for two weeks, can easily lead a vortex of injury in other regions due to deconditioning associated with the reduced game readiness.

Additionally, the bio-mechanics of an athlete cannot be directly correlated to an injury which has not occurred yet – in other words, you cannot predict a specific injury based on bio-mechanical factors that you may visualize. Yes, those bio-mechanical factors can be seen as risk factor for injury but not specifically tied to an individual athlete and the injury they may incur.

Moment in time injuries (ankle sprains/ACLs) and contact injuries of varying degrees will lead to weakness within those tissues and an increase of further injury in the future. This may be a result of “overloaded” tissues relative to their current ability to handle loads – therefore the question is posed again, is it an Overuse Injury, Overload Injury or Training Error which should be the primary umbrella term used to describe these conditions.

The rehabilitation process which has been used to see the athlete return to sport is also important in the contribution to athlete load.

Did the athlete stop all physical activity over the time of injury?
Did the athlete return to training before returning to sport?
Was the athlete returned to their pre-injury chronic load before returning to game play?
Was the athlete 100% ready to return?
If not is the club, player and practitioner willing to take that risk?

There are many more questions that need to be asked and many more which we have not covered here. These decisions are commonly made under pressure to get the player back to field as soon as possible.

Managing Load

So far we have seen what may contribute to an athlete’s load as well as how we can best measure that load in both a subjective and objective format. But how good is that information if we do not have an effective way of managing those risk factors, acute physical load spikes and psychological stressors?

Load should be considered a vehicle, an objective and subjective matter that can drive an athlete towards injury or away from injury. At the end of the day your main destination is “game day performance” or “season performance”, how you reach that destination can be done via a number of routes and selecting the best one is what must be decided upon by the medical staff, athlete and the organization.

When looking to manage load, an athlete’s activity levels should be modified but never ceased. This is to limit detraining, maintain aerobic and anaerobic fitness and continue a base level of their chronic work load. The use of increased aerobic fitness and lower limb strength has been found to reduce an athletes risk of injury. For a long term injury which requires an extensive rehabilitation program it is suggested that workload is increased by 10% per week until the patient reaches their pre-injury chronic workload and are suitable to return to full training.

In conclusion, the monitoring of an athletes load with both subjective and objective measures is essential in the preparation for the competitive season. The development of a well-structured pre-season training plan can bullet proof an athlete not only for a single event but an entire season if completed successfully. A detailed medical history, injury history and lifestyle awareness is important for understanding of how an athlete should prepare for the sporting tasks required of them; from an easy recovery run to a worst case scenario within a single game. It is important to note that an athlete should not stop activity altogether but modify their activities in a way which is most appropriate for their injury.

References

Blanch, P., & Gabbett, T. (2016). Has The Athlete Trained Enough to Return to Play Safely? The Acute: Chronic Workload Ratio Permits Clinicians to Quantify a Players Risk of Subsequent Injury. British Journal of Sports Medicine.

Gabett, T., Hulin, B., Blanch, P., & Whiteley. (2016). High Training Workloads Alone Do Not Cause Sports Injuries: How You Get There Is The Real Issue. British Journal of Sports Medicine.

Halson, S. (2014). Monitoring Training Load To Understand Fatigue In Athletes. SPorts Medicine, 139 - 147.

Saw, A., Main, L., & Gastin, P. (2015). Monitoring The Athlete Training Response: Subjective Self-Reported Measures Trump Commonly Used Objective Measures: A Systematic Review. British Journal Of Sports Medicine, 281 -291.