The physiological and biomechanical limitations imposed on athletes with achondroplasia.
The Little People of America organisation defines dwarfism as a condition that, when a person is fully grown, usually results in a height of no more than 1.2 metres; however a range between 0.8 and 1.4 metres has been recorded (Guse & Harvey, 2010). Dwarfism itself is a blanket term that refers to a person of short stature as a result of a medical or genetic disorder and encompasses over 200 underlying medical conditions (Adelson, 2005). Of these 200 types of dwarfism a separation can be made between proportionate and disproportionate dwarfism, with the former being due to a pituitary deficiency (hormonal) and the latter due to bone growth disorder (genetic) (Porretta, 2011). Types of dwarfism disorders include, amongst others, achondroplasia, pituitary dwarfism, hypochondroplasia and primordial dwarfism; with achondroplasia being most common (Scott, 1976).
Persons with dwarfism are able to participate in sporting activities within the limits of their individual medical condition. There are several organisations that solely promote and run dwarf sport events, such as the Dwarf Athletic Association of America (DAAA) and the Dwarf Sports Association UK; in addition dwarfs are able to compete in the Paralympic games. The DAAA specifically state that events including swimming, track, soccer, and powerlifting are suitable for dwarf athletes.
As with all able-bodied and disabled athletes, to compete at the highest levels in sports dwarfs should be encouraged to participate in a structured strength and conditioning (S&C) programme (Young, 2006). However it is essential that S&C coaches are aware of the limitations imposed by the dwarf athletes’ condition and are cautious of contraindicated exercises and training modalities. Therefore this paper aims to provide guidance as to which training modalities and exercises may be contraindicated in this population, specifically in dwarf athletes with achondroplasia.
Achondroplasia (ACH) is the most common form of dwarfism, affecting 80% of dwarfs, and is characterised by disproportionate (rhizomelic) limbs (Bellus et al., 1995; Guse & Harvey, 2010). ACH is a genetic disorder; it is caused by a disturbance in the conversion of cartilage to bone (endochondral ossification) during fetal development (Laederich & Horton, 2010). The gene responsible for this skeletal dysplasia is the fibroblast growth factor receptor 3 gene (FGFR3), which is found on the distal short arm of chromosome 4 (Bellus et al., 1995). ACH is mostly commonly a sporadic mutation and has been associated with an increased age of one or both of the parents (Rousseau et al., 1994). It can, however, also be inherited as an autosomal dominant trait, meaning that even if only one parent passes on the FGFR3 gene, it will be inherited by the child (Bellus et al., 1995).
Athletes with ACH display a multitude of noticeable physical characteristics of which the majority result in clear physical implications to consider during exercise. Particularly obvious characteristics include relative macrocephaly (large skull) and frontal bossing, rhizomelic limbs (shortened humerus and femur), genu varum, lumbar lordosis and small, broad hands and feet (Bellus et al., 1995; Kitoh et al., 2002; Wagner & Sandt, 2012).
As expected from a skeletal dysplasia, athletes with ACH typically have a rhizomelic shortening of the, normally long, proximal extremities: the humerus and femur (Bellus et al., 1995; Kitoh et al., 2002; Wagner & Sandt, 2012). Although the skeleton is affected, the other tissues of these limbs are not; therefore they continue to grow normally resulting in bulky arms and legs (Guse & Harvey, 2010). Although this abnormality is most obvious in the proximal segments, the distal segments are still characteristically short, with research showing a normal tibia/femur ratio (Haga, 2004). The proximal portion of the fibula, however, is prone to overgrowth and contributes to the genu varum/bow leg deformity noticed in athletes with ACH (Bellus et al., 1995; Kopits, 1976; Ogden, 1979). Genu varum in ACH is also due to laxity of the lateral collateral ligament (Haga, 2004); this laxity is also present in all ligaments meaning that these athletes are often classed as ‘double-jointed’, which presents obvious implications for training (Ireland et al., 2011; Wagner & Sandt, 2012).
Ligamentous laxity, along with deformities to the athlete’s joints, can cause serious issues with achievable ranges of motion, contributing to an increased likelihood of them sustaining an injury (Wagner & Sandt, 2012). Joints of adult athletes with ACH are generally very small in circumference, similar to that of a child, which is a factor that clearly must be considered when exposing one of these athletes to high loads due to the degree of force going through the smaller joint (Bailey, 1971).
One of the most common joint abnormalities in athletes with ACH is the lack of ability to achieve a full extension of the elbow joint (Bailey, 1971; Bellus et al., 1995; Kitoh et al., 2002). This range of motion deficit is thought to be due to a deformity of the distal part of the humerus whereby the metaphyseal area ‘flares’ outwards (Haga, 2004). Another mechanism behind this abnormality is the subluxation of the radial head, something common in this population, also known as a ‘pulled elbow’ (Kitoh et al., 2002). Other notable issues related to the limbs include a shortness of the fingers, hands and feet (Wagner & Sandt, 2012) and a limitation in hip extension which is linked to the hyperlordotic curvature of the spine (Haga, 2004).
Spinal deformities, particularly an increase in the degree of spinal curvature, are typical in athletes with ACH (Jarvis, Cook, & Davis, 2011). Excessive lordosis of the lumbar spine and kyphosis at the thoracolumbar junction has been observed and, according to Haga (2004) this exaggerated curvature can lead to neurological deficits. Spinal stenosis, a compression of the nerve roots due to narrower than normal vertebral foramen, can occur causing physical disablement due to spinal claudication (Haga, 2004). This can be caused by the aforementioned lordosis and kyphosis, and additionally but shortened distances between the pedicles of vertebrae (Haga, 2004; Vanlandewijck & Thompson, 2011).
Although possessing smaller lungs than able-bodied athletes, the lungs of athletes with ACH are appropriately sized for their body size and function normally (Wagner & Sandt, 2012). Research has demonstrated that athletes with ACH have a lower stroke volume and vital capacity when compared to athletes without ACH; however this can again be explained by their reduced thoracic volume (Takken et al., 2007). These condensed capacities are, however, made up for by these athletes with higher respiratory rates and pulse rates during exercise (Wagner & Sandt, 2012).
Other marked characteristics include, firstly, a predisposition to gaining excessive bodyweight due to have less body area to distribute extra mass on (Wagner & Sandt, 2012). This may exacerbate several of the previously mentioned issues including joint problems, lordosis, spinal stenosis and genu varum (Hoover-Fong et al., 2008). And secondly a certain degree of hypotonia may also be present, noticeable as a decrease in tension and stiffness of the musculature, which may contribute to the unusually high degree of laxity in the athletes joints (Jarvis, Cook, & Davis, 2011; Wagner & Sandt, 2012).
For the S&C coach working with an athlete/s with ACH, it is essential that the limitations and conditions above be taken into consideration. The following content covers some key training recommendations and contraindications to bear in mind when training one of these athletes.
As with all athletes a throughout assessment should be undertaken before beginning a training programme; for athletes with ACH some specific tests should be employed. Initially a postural assessment to determine spinal curvature should be used (Vanlandewijck & Thompson, 2011); this establishes degrees of kyphosis, lordosis and scoliosis in the spine. With this information it is possible to decide to what extent an athlete should be loading axially whilst preventing compressive injuries to the vertebrae. The nine-point Beighton laxity scale can be utilised to measure joint/ligament laxity (Beighton & Horan, 1969), indicating whether it is safe to perform exercises requiring a wide range of motion. Finally a simple functional-movement screen (Cook, Burton, & Hoogenboom, 2006) will show any movement restrictions.
During training session’s proper body positioning and biomechanics must be ensured in order to prevent injury to the spine and limbs. It is good practice to maintain a neutral spine during lifting exercises (Burnett et al., 2008), however in exercises such as the powerlifting style bench press it is common to promote an extreme ‘arch’ in the thoracic spine. This is contraindicated in this population due to their narrower vertebral foramina (potential for stenosis) and it is therefore pertinent that a more gradual arch be used, with thoracic extension from all spinal segments (Richens, 2014). Exercises for the anterior musculature of the trunk may be beneficial in resisting extension and maintaining neutral spine (Katz & Harris, 2008).
When planning a session, particularly for conditioning, it should be accounted for that these athletes have smaller limbs and thus may fatigue faster (requiring rest periods more often) and will find distances harder to cover; as roughly three steps of theirs compares to one step of a normal statured person. In addition, it may be beneficial to use smaller training implements. An example of this is to use a ‘female’ barbell as opposed to a thicker men’s barbell as, due to smaller hands, the athletes fingers cannot close around the bar fully (giving the feeling of a ‘fat bar’) which can lead to excessive wrist extension and injury (Richens, 2014). Other intra-session/planning considerations are presented in Figure 1.
In summary, an S&C coach must consider and assess the individual limitations imposed on athletes with ACH and be prepared to make alterations when planning and coaching sessions in order to allow these athletes full participation. Protection of the spine through the maintenance of correct posture and technique is paramount, thought should be given to exercises that may cause trauma to joints and there should be consideration of the athlete’s ability to complete certain exercises and ability to cover distances.
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