The effects of strength and balance training on fatigue related injury risk
by Bsc. Sport Science, Martin Kvist for Partner Acrobatics

February 21, 2014


Fatigue is an inevitable part of exercising, and fundamental to create the necessary training stimulus for increases in performance and adaptations to occur, but with the presence of fatigue comes increased injury risk Woods et al. (2003); McLean & Samorezov (2009). In acrobatic sports the frequency of injury and the presence of pain is a major limiting factor to any long term training and performance goal Purnell et al. (2010). However the current consensus in the field of injury prevention is that most of the processes related to fatigue, that are suspected in leading to injury and pain, are trainable Schiftan et al. (2014); Woods et al. (2003); McLean & Samorezov (2009); Greig & Walker-Johnson (2007).
This article briefly introduces the concept of fatigue and how it is related to injury, it gives a quick look at the injury rates in acrobatics, and the specific adaptations of the nervous system with certain types of training, that seem to be key in promoting stability and preventing injury. Namely the effects of strength and balance training on the nervous system, and how these effects functionally can lead to improved injury prevention in training planning.



Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle (peripheral fatigue), but also because the central nervous system fails to drive the moto-neurons adequately (central fatigue) (McArdle et al., 2010, p. 393).
Several studies have provided evidence for correlations between the risk of specific sport injuries, and the effects of fatigue McLean & Samorezov (2009); Schiftan et al. (2014); Woods et al. (2003). For example muscular fatigue has been related to the incidence of injuries in soccer, as most injuries are observed during the last third of each half of matches Woods et al. (2003).
Fatigue is inherently a part of exercising and it's not that we want to avoid becoming fatigued, however it is worth taking into account in our training planning, and preparation that there are imbalanced patterns at the core of injury causality, and that these compensations can be identified, and prevented through targeted training. In acrobatic sports there is a prevalence of shoulder issues, carrying your bodyweight overhead in a handstand requires a high degree of overhead shoulder stability and a proper balance in the engagement of the shoulder muscles. In overhead athletes, like the volley ball player hitting a ball or the acrobat performing a handstand, the activation pattern of the shoulder muscles play a key role in how the different structures of the shoulder joints are loaded. If the athlete has imbalances in this activation pattern, like certain muscles being over activated and thus overpowering other muscles, there is a risk of placing high loads on the shoulder joint in a unstable or un-advantageous position, ultimately leading to pain and injury.
For example a recent study into how Glenohumeral external rotation muscle fatigue might contribute to shoulder injuries in overhead athletes, highlights the interdependence of scapular and glenohumeral force couples, in other words the importance of a proper balance between the muscles that act on the shoulder. Fatigue-induced alterations in the lower trapezius (Trap-3) might predispose the infraspinatus to injury through chronically increased activation Joshi et al. (2011). Targeted training of the lower trapezius and the external rotator muscles of the shoulder is thus a highly recommended injury prevention strategy for overhead athletes, and will help the acrobat a lot in stabilizing the shoulder joint when performing the handstand.

Fatigue & Injury

Injury causality and prevention is a very complex field, often conflicting evidence arises for the assumption, that fatigue induced alterations in activation pattern are causing instability of a joint. For example there is a specific recruitment sequence in the shoulder muscles in response to a sudden arm movement, and one study concluded that this muscle activation pattern is delayed but not altered with fatigue Cools et al. (2002) and another study by Joshi et al. concluded that fatigue-induced alterations in the lower trapezius might predispose the infraspinatus to injury through chronically increased activation. Despite the conflicting evidence in regards to the effect of fatigue on muscle activation pattern, most studies agree that there are correlations between fatigue of central control processes, and injury risk.
Looking at the effects of fatigue on stability, it seems that even though balance performance is maintained throughout the exercise, a change in balance strategy is evident during the latter stages, with a shift toward anterior displacement, such compensatory strategies might increase the risk of injury to both muscular and ligamentous structures, particularly in more dynamic movements Greig & Walker-Johnson (2007). Furthermore fatigue of one leg induces a fatigue crossover to the other leg during single-leg landings. Central fatigue thus seems to be a critical component of fatigue-induced sports landing strategies. Hence, targeted training of central control processes may be necessary to successfully counter the debilitative impact of fatigue on specific injury risk McLean & Samorezov (2009).

Besides shoulder injuries and ankle sprains, low back pain is a prevalent issue for many acrobats Purnell et al. (2010), and a direct relationship between low back pain and neuromuscular imbalance has been documented, in athletes with low back pain Renkawitz et al. (2006). In patients with chronic low back pain, muscle recruitment was also altered with the presence of muscle fatigue Abboud et al. (2014). Interesting to note here is, that even though strength training has shown to be an effective treatment modality for low back pain, Maximum isometric trunk extension strength had no relationship to the presence of Low Back Pain or the occurrence of neuromuscular imbalance of erector spinae Renkawitz et al. (2006). A study by Hashemirad et al. (2009) indicates that flexibility plays an important role in trunk muscular recruitment pattern and the strategy of the central nervous system to provide stability. What to take from this is that even though we do not fully understand the processes of fatigue that result in injury, one evident principle is that effective injury prevention involves proper neuromuscular balance, targeted training of central control processes and range of motion.

Injury rates

If we look at the stats, not that many studies have focused on partner acrobatics, but it won't come as a surprise that the floor can be dangerous, the floor has been identified as the most hazardous of all the apparatus on which gymnasts perform. Acrobatic routines involve similar skills to gymnastic floor routines, with the additional physical stresses of partner balances and throws, and we see injury rates of 2.94 per 1000 h of participation, or 1.21 injuries per acrobat per year, which is slightly lower than artistic gymnastics but higher than cheerleading. The higher injury rate in acrobatics compared with cheerleading is expected as the ratio of bases to tops is often greater in cheerleading group skills, hence the load of the top is spread amongst more bases. Purnell et al. (2010).

Training specific reflex adaptations

When an injury results in acute pain, the nervous system undergoes an adaptive neuroplastic response resulting in an increase in sensitivity. After some time, the pain neuroplasticity is normalized as the injury heals. In some cases, such neuroplastic processes fail to normalize, and acute pain develops into chronic pain with hypersensitivity. The continuing pain after injury resolution may be due to maladaptive pain neuroplasticity. In contrast, advantageous neuroplasticity permits the nervous system to cope with challenges such as maladaptive pain neuroplasticity to help returning to a pain-free state Navarro (2009).
Spinal reflexes where previously viewed as stereotyped motor patterns with limitid scope for modification. However, evidence suggests that even short-latency, largely monosynaptic reflexes show a high degree of modulation during simple human motor activities such as walking and standing, and that the pattern of modulation can be specifically altered for the different functional requirements of each activity Stein & Capaday (1988). This is further supported by the evidence for adaptations in reflex excitability that are specific with respect to the type of training. For example Trimble & Koceja (1994) provided evidence for reflex down-training in man during balance training. This Reduced reflex excitability have been demonstrated for both power- and balance-trained athletes Gruber et al. (2007).

The effects of strength and balance training

Some controversy remain but several studies have provided evidence, that balance and strength training induce changes in short latency reflexes and that these reflex adaptation forms part of the neuroplasticity induced by specific training Komi (2003); Gruber et al. (2007). A reduction in reflexes could be associated with either neural adaptations or a shift in muscle fiber distribution after a sustained Strength training over several months Gruber et al. (2007). Functionally this reduction in reflex excitability could enable more cocontractions of muscles associated with postural controle, thus creating better stability. Neuromuscular control and Proprioception the sensory feedback from muscles and joints about position, length, etc are fundamental factors in preventing injury. It is therefore recommended that athletes perform proprioception (balance) and neuromuscular balance (strength) training in the rested and exercised state to further develop neuromuscular control Schiftan et al. (2014); Greig & Walker-Johnson (2007).

While we are learning and as we progress in our practice, we intuitively know that the more hours we rack up in training the higher our probability of sustaining an injury becomes. Statistics dictate that with increased training load comes increased injury risk, either from a fall (sudden onset injury) or from inadvertently overloading soft tissues and joints during practice (overload /specialization injury). Risk is part of what makes acrobatics fun, we embrace the risk of getting hurt that is inherent to playing, but just as we use spotters to minimize the risk of falling, we want to condition ourselves in a way that minimizes the risk of overload or specialization injuries.
The causality patterns of most sport injuries are multi factorial in nature, but freak occurrences and shear bad luck a side, fatigue related mechanism like alterations in muscle activation pattern, or reinforced compensations due to neuromuscular imbalances, are suspected in leading to adverse loads being placed on different structures of the body ultimately leading to pain or injury McLean & Samorezov (2009); Meeuwisse et al. (2007). With these patterns being trainable through strength and balance training, it is evident that a little effort in targeted training can lead to improved injury prevention in acrobatic training.

Conclusion & Application in training planning

In this article we have looked at some of the correlations between fatigue and sports injury, one evident principle is that neuromuscular balance and control, are fundamental factors in preventing injury. Stability and neuromuscular control involves reflex adaptations, specifically reduced reflex excitability, that functionally allows for more co-contraction of muscles associated with postural control. With reduced reflex excitability having been demonstrated for both power- and balance-trained athletes Gruber et al. (2007), strength and balance training are key elements of promoting stability and neuromuscular control. The recommendation for acrobats to train for injury prevention is targeted training of the lower trapezius and the external rotator muscles of the shoulder, plus targeted training of proper neuromuscular balance of the low back/ hip area. Because of the similar reflex adaptations with balance and strength training, a fundamental element in preventing injury and improving performance in acrobatics, is thus strength training focused on proper neuromuscular balance.


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August 15, 2015


From a sports scientific point of view, a Sport-specific strength training program is fundamental to an athlete’s development and success. Long gone are the days when coaches shunned weight lifting for fear that it might hinder the performance of fine skill and correct technique. It’s now accepted that high levels of strength are a prerequisite to superior speed, power, strength endurance and overall sporting performance [ (2014); National Strength and Conditioning Association (2008)]. From this point of view one of the best ways to train for acrobatics would be using a periodized training plan, and spending more than 2/3 of the time on specific conditioning like sports specific strength training [Demey and Wellington (2010); Eubanks and Gonza- lez (2009)]. For increasing performance it is widely agreed in the field of sport science, that resistance training with compound exercises, done at exercise in- tensities between 60 - 80 % or even higher, if the athletes condition allow it, is a highly effective way to increase performance [Andersen and Aagaard (2010); Kraemer et al. (2002)]. For example, if you are doing weightlifting this means exercising with weights that are close to or above 80% of your one repetition max ((1 RM) the weight you can lift once and only once). There are many simi- larities between the movement patterns and metabolic demands of weightlifting and acrobatics, this makes weightlifting a great way to condition yourself for ac- robatics, both in the sense of increasing performance and in terms of preventing injury by creating a proper balance of strength and neuromuscular activation.

However most of the athletes practicing partner acrobatics and acro yoga are not competing athletes, and are not training using a periodized training plan. As the European federation of professional circus schools (FEDEC) writes in their manual ”Theory, guidance & good practice for training”, by Demey and Wellington

In acrobatics and circus training there is a huge variety of approaches that trainers and students can take to prepare themselves physically. Frequently an ad hoc approach is taken when implementing physical conditioning, which is often unplanned and with no sound justification. Physical preparation should not rely so heavily on guesswork and luck (Demey and Wellington, 2010, p. 8).

What can we do in our practice to use some of the principles of proper training planning in our favor, when we don’t train for competitions and just want to learn the handstand and play?


Principles of training

One of the main principles of periodization is variation in the training stimulus. In order for adaptations to occur, the training load or stress needs to be suffi- cient. The neuromuscular system will adapt to these stressors, so the training stimulus must constantly be varied in order to create further adaptations [De- mey and Wellington (2010); McArdle et al. (2010)]. The principle of specificity states that training should mirror the demands of the sport as closely as possible [Kraemer et al. (2002)]. This applies not only to way the body’s energy systems and neuromuscular system is taxed (through ma- nipulation of intensity and rest intervals etc) but also to the movement patterns of each exercise [McArdle et al. (2010); National Strength and Conditioning Association (2008)]. Several studies have shown that strength and balance training promotes adaptations of the nerveous system, in the form of a decrease in the stretch re- flex excitability [Stein and Capaday (1988); Trimble and Koceja (1994); Gruber et al. (2007)]. The importance of this from an acrobatic training perspective, is that with similar adaptations of the nervous system from strength and bal- ance oriented training, like acrobatics, we can achieve skills faster and increase our performance through strength training. Furthermore this adaptation is considered to promote stability around a joint by increasing the capacity for co- contracting the muscles [Gruber et al. (2007)]. However the stability achieved by co-contraction of opposing muscles are highly dependent upon a proper bal- ance of strength and neuromuscular activation. Specific strength training have been shown to be an effective tool to promote balance in neuromuscular activa- tion, strength ratios of opposing muscles and in increasing overall performance. The recommendation based on this is thus that for acrobatic training, doing resistance training with this focus is indeed a sensible approach to conditioning and general preparation for doing acrobatics.


Acrobatic practice has many benefits, and it may seem to be a very diverse form of movement, but if you look at the individual joint movements like flexion and extension of the hips and shoulders, or pushing and pulling movements of the arms and legs. It can actually be broken down into a few specific movement patterns, not only in practicing the handstand but in both basing og flying there is a lot of pushing through the shoulder movements and only very few pulling movements. This seem to create a pattern of similar shoulder impingement issues as those seen in overhead athletes like volleyball players, and indeed there is a prevalence of shoulder injuries in acrobatic sports Purnell et al. (2010).
Figure 1: Flexion and extension movements of the hip and shoulder
Another specialized pattern of movement done repeatedly in acrobatics is the closing of the hip joint, especially in L-basing, this shortening pattern of the hip flexors are being reinforced repeatedly during practice. Figure 2: Pushing through shoulder movements
The point being that as any sport if you practice regularly, even diverse forms of movement like acrobatics, becomes a highly specialized form of training with some movement patterns being done repeatedly. With specialization comes certain pitfalls, and doing the same movements re- peatedly will strengthen only certain muscles and movement patterns, over time this can lead to patterns where certain muscles becomes too active and/or tight, thus overpowering others, and mis-advantageous compensations may arise.


In athletic training one of the tools used to avoid this negative effect of spe- cialization, and improve the performance of the athlete is Periodization wich is the systematic cycling and variation of the training stimulus [Garrett and Kirk- endall (2000)], It involves progressive cycling of various aspects of a training program during a specific period. Periodization divides the year round condi- tion program into phases of training which focus on different goals. A good example of a periodized training plan for acrobatic gymnastics can be found in Eubanks and Gonzalez (2009).
Figure 3: Usually the year is divided into three phases: preparation, competitive, and tran-
sition. The aim is to reach the best possible performance in the most important competition
of the year.
A significant challenge is how to design a training programme that facili- tates muscular and neurological adaptations whilst respecting the healing rate of the body’s tissues and maintaining safety of the individual. It must be re- membered that there are many different elements that contribute to successful performance, not just the physical conditioning program Demey and Wellington (2010), Proper sleep and nutrition are also fundamental to successful perfor- mance and recovery McArdle et al. (2010).
Now we may not be competing athletes but we can still benefit from applying the principles of periodization in our approach to conditioning. It involves pro-gressive cycling of various aspects of a training program during a specific period. We know that there is no one ”cure all” exercise and using periodization enables us to choose from many different exercises and progressions, implementing them at different times in our training. Planning your training will help avoid injury and increase your performance

Variation and Balance in training.

So how do we use these principles when we don’t plan our training? For example, Let’s say you really want to be able to do a handstand, so you practice for 4 hours a day doing handstands, and after a while your shoulders hurt. Maybe you should think of varying your training stimulus! Doing hand- stands is like repeatedly pressing your body weight overhead in the gym, if you only press, the muscles that do the pulling get compromised. So instead of re- peatedly doing handstands 4 hours a day, vary your training. You could maybe spend one hour or more, climbing or doing pulling movements in the gym. This will not only help to keep you injury free, but there is also significant neuro- scientific evidence to back that a more varied approach in practice will actually make you learn faster and retain more of what you learn Zetou et al. (2014); Breslin et al. (2012); Magill and Hall (1990); Proteau et al. (1994).

  • Vary your training stimulus and movement patterns! like doing climbing to balance out your handstand training..
  • Think about balance in your training and movement patterns! Like doing pulling to balance out the pushing of the handstand training..
  • Hip opening to balance out and vary the closing of L-basing etc..


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Contact me to get started on your program now!

Master of Science in Sports, Martin Kvist.

Partner Acrobatics teacher trainer and CEO of Flying High Acrobatics 

Highly educated in the field of sport science, neuroscience, and motor learning. Martin’s ability to provide injury prevention support, inspire healthy movement, and passion for acrobatics is essential for students who want to delve deep into their bodies for maximum strength and healing.