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Hyperflexion in horses

Author Name: Gemma Humphrey; BSc (Hons) Equine Science



Training methods where the horse is expected to maintain a hyper-flexed position are currently under scrutiny due to potentially resulting in compromised equine welfare. Research has suggested that the neck plays a key role in equine biomechanics. For example, a high and elevated neck was found to increase hock action in the horse. Recent research has also suggested that there may be detrimental effects to the horse’s welfare due to the use of hyperflexion, such as the increased chance of strains and airway constriction. However, the methods used in this research possess limitations such as, for example, the use of cadavers to analyse the muscle structure in the neck. One study used a sample of cadavers aged 8-11 months with the findings being applied to a population of fully grown dressage horses, without taking into account the effect of training and exercise responses. Other research has however assessed the use of hyperflexion during training where the horses’ displayed a decrease in cortisol levels, potentially indicating reduced stress. Overall, the research is conflicting in terms of whether hyperflexion is compromising equine welfare however this work has a number of limitations which makes it difficult to determine if hyperflexion is detrimental to horses’ health. More research needs to be performed looking specifically at case studies on rider ability and to determine whether horses are experiencing pain and discomfort from this particular training method.


1.0  Introduction

Ewers (1995) was one of the first studies to suggest that the position of the head and neck (HNP) could potentially cause pathological locomotor disturbances. Further research supported this and suggested that the (peri-)neuritis in partnership with the myelopathy and facet joint could result in discomfort to the horse, similarly to as is seen in humans (Dunbar et al. 2008; Moore et al. 1992). Since then, more research has been encouraged to explore the effects of HNP’s used in various equestrian training methods, particularly, dressage (McGreevy et al, 2010).

The training method ‘Rollkur,’ also known as hyperflexion, has provoked much debate amongst equestrian people (Elgersma et al, 2010). Hyperflexion is a method where the rider requires the horse to provide a specific amount of longitudinal flexion of the neck (Zebisch et al, 2014a). Hyperflexion is controversial due to the unnatural position that the horse is expected to maintain during training. It has been suggested that hyperflexion may  be detrimental to the horse’s health (Zebisch et al, 2014b). Examples of welfare concerns include behavioural changes and airway obstruction (Kienapfel, 2015). As a result of the potential negative impacts of hyperflexion, the Code of Conduct approved by the Federation Equestrian International in 1990 may have been breached (FEI, 2016a). However in contrast, other research has potentially found benefits of hyperflexion which may improve specific musculature and psychological aspects in the equine athlete (Van Breda, 2006). In this critical review, the potential positive and negative effects of hyperflexion are discussed.


2.0  Critical Review

2.1 Physiological Impacts of Hyperflexion

High positioning of the HNP was believed for a long time to be an influencing factor for the range of motion of the forelimb (De Carpentry, 1972). Hind limb engagement was also a supposed effect of a high and flexed head and neck (Liart, 1951). More recent research, using a treadmill, suggests that exercise in the unridden horse, with a flexed HNP, increases the range of motion in the equine lumbar back. This allows the horse to be more balanced by acquiring a greater hock action  (Gomez-Alvarez et al, 2006). This study’s findings are beneficial for improving the dressage horses’ ‘way of going’ (McGreevy et al, 2010). However, Rhodin et al (2009) had contradictory findings as they found no increase in motion within the lumbar back with a flexed head and neck position in ridden horses. They also used a treadmill to assess the biomechanics of the horse.  By using a treadmill to analyse gait movement in horses with a flexed HNP these two studies were able to control speed and terrain which increased the reliability of their findings. However, a treadmill has been found to influence gait within the horse due to momentum and air resistance therefore the results could be invalid (Lane et al, 2006). In addition, the two  studies both used side reins to create HNP’s. This can be argued as a false representation of the correct outline, therefore more research is needed to support the above findings (Oedberg and Bouissou, 1999).

Recent research has focused on the different angles of HNP during exercise in order to attempt to objectively test a true representation of HNP’s currently used in dressage (Rhodin et al, 2009; Waldern et al, 2009; Weishaupt et al, 2006). Elgersma et al (2010) attempted to develop an objective method to determine loading on the cervical vertebrae using the six validated HNPs. Markers were glued onto specific areas of the horse’s head and neck and horses were videoed when walking in order to determine loading of the cervical vertebrae. Radiographs were also taken. The methods of this study could be criticized due to the potential displacement of markers which could render measurements of angles for the HNP’s unreliable. However, this study compared their findings with ex vivo analysis in order to validate their longitudinal angles between the vertebrae, improving the validity of their results. Elgersma et al (2010) found that throughout the nuchal ligament, loading was greatest at C2 in hyperflexion which may increase the likelihood of muscular pain (HNP4). In support of this, Nestadt et al (2015) found a 13% increase in funicular length within the nuchal ligament when five late-term foals were dissected and positioned in hyperflexion. The increase in funicular length during hyperflexion was suggested to increase the potential for strains in the nuchal ligament due to the excessive stretching. However, a limitation of the above study was the unknown age and breed of the foals which may be problematic when attempting to apply the findings to fully grown sport horses. Although, the late-term foals were all between 8-11 months of gestation, and therefore skeletal properties and mechanical processes would already have been fully developed, they would not have obtained the relevant training responses (Valera et al, 2006). Gellman and Bertram (2002) also found that the nuchal ligament becomes significantly stretched when the horse flexes their neck over 25 degrees which may increase the likelihood of strains. In this study, horses were analysed on a treadmill though so the validity of the results may be reduced due to the artificial environment. In addition, hyper flexed positions in the horse’s head and neck have been linked to injuries in the fetlock joints, due to a significant amount of hyperextension being found in the joint compared to other head and neck carriages (Kienapfel, 2015).

In humans it is known that extension of the cervical spine causes a decrease in intervertebral foramina dimensions whilst flexion encourages an increase. It was unknown whether flexion and extension influenced nerve and muscle functioning in the equid. However, Sleutjens et al (2010) used tomography on six cervical spines from adult horse cadavers. In this study measurements of the intervertebral foramina were obtained in different degrees of flexion and extension. The result for equids, regarding the effects of  flexion and extension on intervertebral foramina dimensions, were very similar to that seen in humans (Ebraheim et al, 2006; Humphreys et al, 1998). More research needs to be carried out to understand the effects of hyperflexion on nerve and muscle function in a sample of live dressage horses using a validated method. It has been suggested that pressure algometry may be a beneficial method to analyse muscle function, particularly sensitivity (De Heus et al, 2010). Pressure algometry is a procedure that determines the minimum pressure to cause a pain response. This is known as a mechanical nociceptive threshold (MNT), with higher values being associated with little pain and low values indicating pain or sensitivity. De Heus et al (2010) analysed factors such as muscle tone, pain and mobility using algometry. They found that the findings from the algometer concurred well with the opinion of physiotherapists. Menke et al (2016) studied the effectiveness of algometry in Icelandic horses by comparing the values of two participants. Values differed slightly between the participants indicating that there is a skill to the use of the algometer. Results of algometry studies may therefore be affected by the experience of the experimenter in using the algometer. This method could however be an efficient way to determine if hyperflexion compromises equine welfare or impacts on muscle function.


2.2 Airway Obstruction

It is suggested that hyperflexion in the ridden horse may restrict the diameter of the airways. Desmaizieres et al (2008) determined that the final dynamic respiratory scope (DRS) is a beneficial tool for obtaining endoscopic images of the upper respiratory tract in ridden horses. The DRS is an easy and applicable method with no habituation period being necessary for participants (Franklin et al, 2008). The DRS is much more reliable compared to endoscopy used on a treadmill in exercised horses, due to the different structure of the insertion tube which produces clearer images (Franklin et al, 2008). As a result of this approach, Zebisch et al (2014a), were able to take video recordings of the larynges of 14 horses in order to investigate the effects of different HNP’s on the upper respiratory tract in ridden horses. This study found that the height of the larynx hardly changed in relation to the HNP’s, however there was a reduction in the opening area whilst the horse carried out the hyperflexed position. One advantage of this approach is that the study carried out a preliminary test to determine the parameters used in the study, such as the height and maximum width of the laryngeal opening area. However, one limitation to the method was that only a percentage of size comparison was used for the measurements as it was not physically possible to use a measuring tool for the upper respiratory tract during ridden exercise. The reliability of the results are therefore reduced as the measurements may have lacked precision or been affected by the subjective opinion of the researcher.

In support of the above study, Cehak et al (2010) found that the pharynx will narrow when the horse flexes their head and alternatively that the pharynx will widen when the horse extends their head. This study suggests that when the horse is in any flexed HNP the airway in the upper respiratory tract will constrict in comparison to the normal head carriage. Moreover, further research has linked airway obstruction to rider interactions which has been suggested to cause complicated upper respiratory airway obstruction (Van Erck, 2011). Therefore, it could be argued that hyperflexed positions may not be restricting in themselves but that instead rider ability and interactions may influence the effects of the particular training method.


2.3 Psychological impacts of Hyperflexion

The FEI (2016a) state that the horse’s welfare should be paramount at all times within equine sport, however research has suggested that hyperflexion may cause stress in the horse. Zebisch et al (2014b) investigated the influence of two different HNP’s on stress parameters of 18 ridden horses. They concluded that hyperflexion led to an increase in cortisol levels which can indicate stress. The HNP’s used were scientifically validated (Rhodin et al, 2005). However, the HNP’s in Zebisch et al (2014b) study were obtained without the use of draw reins with the aim to create a more realistic situation. By not using draw reins this could potentially improve the validity of the results, in comparison to other studies that have used draw reins which could create a false outline of hyperflexion (Oedberg and Bouissou, 1999). A limitation of this study however, may be the lack of standardised HNP positions, as rider ability may reduce the reliability of the results by not keeping the horse in the hyper flexed position. Six of the horses were ridden by a professional rider and 12  were ridden by a successful amateur. Becker-Birck et al (2013) found that when lunging horses in the hyper flexed position, no acute stress was apparent. Therefore, it could be argued that rider ability may be a factor for inducing stress to the horse.

Moreover, Van Breda (2006) found that elite trained dressage horses tended to have less acute stress, based on heart rate variability post exercise, compared to ‘recreational trained’ horses. This suggests that elite dressage horses have significantly lower heart rates after undertaking hyperflexion post exercise because they practise the technique daily compared to recreational horses that do not. In contrast, Sloet van Oldruitenborgh-Oosterbaan (2006) found no signs of stress from a sample of eight recreational horses who had experienced hyperflexion during the experiment. They examined cortisol, packed cell volume and glucose levels. However, cortisol levels can easily be disrupted by physiological and physical stress which may reduce the validity of the results (Zebisch et al, 2014b). In addition, Sloet van Oldruitenborgh-Oosterbaan (2006) used side reins in the study to create the hyper flexed position, which is argued to be a false representation of hyperflexion as the horse is fixed in the position. This could also reduce reliability of the results (Oedberg and Bouissou, 1999). That said, both of the above studies used the same breed of horses in their sample. This is beneficial when investigating hyperflexion as conformation can affect how well a horse can perform it (McGreevy et al, 2010).


2.4 Impact of Hyperflexion on Behaviour

For most riders, obtaining the correct head and neck position for a horse during training is a vital element in order to excel in the discipline of dressage (McGreevy, 2007). The FEI states that any HNP acquired in the horse during any exercise should not be obtained by aggressive force as this is unacceptable (FEI, 2016b). However, McGreevy et al (2010) found that 68% of 828 horses pictured in photographs had their nasal plane behind the vertical with a significant arching of the neck. This was a desirable position for advertisers from magazines. The FEI (2016b) believe that horses in the above study were ridden more incorrectly than correctly. Incorrect training of neck flexion consists of constant rein pressure along with sustained cervical flexion with no release of pressure (McGreevy, 2007). Acquiring a HNP with an aggressive force may significantly compromise welfare and learning  (McGreevy et al, 2010). If the horse learns that there is no way to escape the pressure this may lead to conflict behaviour such as rearing, kicking or bolting (Van Breda, 2006).

Borstel et al (2009) found significant behavioural changes during hyperflexion compared to other HNP’s such as tail swishing, bucking and head tossing. Furthermore, horses were more compliant to moving forwards in an unrestricted HNP compared to hyperflexion, suggesting that this position may cause discomfort for the horse (Borstel et al, 2009). This study used observation along with an ethogram to assess behaviour which may have associated issues with researcher subjectivity which could reduce the reliability of the findings. It could also be argued that horses were less compliant to going forward due to the increase in workload during hyperflexion compared to other HNP’s (Sleutjens et al, 2013). Alternatively, a horse may be less compliant to go forward in hyperflexion due to a lack of training and they may become confused with the rider’s aids; rein pressure asking for flexion and leg aids for going forwards (McGreevy, 2007).

In addition, constant rein pressure on the bit may not only deaden the breaks and encourage dangerous behaviour but also the horse may experience learned helplessness as they have no escape from the pressure (Goodwin et al, 2009). This research along with other supporting studies encourages more training for riders, as well as for trainers to be skilled and aware when learning is being compromised, in order to ensure welfare of the horse is paramount (McGreevy, 2007). Furthermore, a number of equestrian organisations have explained that increasing the amount of neck flexion may become counterproductive and the horse will go on the forehand (Warren-Smith and McGreevy, 2008). More research is needed to assess rider ability relative to the horse’s ‘way of going’ and case studies may be potential methods to assess this. Although, case studies can be time consuming, they will provide in depth information about the factors that influence hyperflexion in the horse (McGreevy, 2007).


3.0 Conclusion

Overall, there is much research that suggests that hyperflexion causes detrimental effects to equine welfare. However, this research possesses limitations such as invalid HNP’s  being used compared to that of the dressage horse in training, as well as concerns about the reliability of the stress measures used, such as cortisol.  Therefore, even though there is a large amount of research suggesting that hyperflexion is affecting the horse’s health, there are still concerns with applying these findings to the equine dressage population. Other research has found beneficial effects of hyperflexion such as improving balance and motivation in the ridden horse. Research in this field is relatively limited and more studies need to be carried out, such as looking at case studies of riders who believe that their horses benefit from hyperflexion. One factor that could impact on whether hyperflexion is damaging to the horse is rider ability or lack of training from the individual. Further in-depth research into this should be carried out.



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