Calcaneal Bone Quality and Physique in Elite Hungarian Male Athletes.

Abstract
Regular physical activity has favourable influence on the bone status. The purpose of this study was to analyze the relationships between the bone quality index (BQI) in the calcaneus and anthropometric variables in male elite athletes. Participants were Hungarian elite male athletes: kayak-canoe (KC, n=43); triathlon (T, n=16); track & field (TF, n=46); water-polo (WP, n=19). Their physique was characterised by Heath-Carter somatotype. Calcaneal Quantitative Ultrasound (QUS) parameters were registered by Sonost3000 densitometer. Differences in bone quality between the groups and correlation patterns between QUS and physique were analysed (p<0.05). There were significant differences in QUS parameters. T and TF had significantly higher SOS (speed of sound, m/s) values than WP. KC had lower SOS values than T athletes (TF: 1519.3±16.0; T: 1512.9±20.8; KC: 1505.6±12.4; W: 1495.1±10.8. BUA (broadband ultrasound attenuation, dB/MHz) was the largestest in TF but this only differed significantly from WP (TF: 106.5±14.8; T: 98.9±11.5; KC: 98.7±16.5; WP: 92.2±8.8). BQI (αSOS+βBUA) was higher in TF (92.0±16.7) than in KC (79.2±13.1), WP (69.3±10.0); it was higher in T (84.8±19.6) than WP. Muscle percentage correlated positively, while absolute bone measurements correlated inversely with bone parameters. Higher QUS values were associated with lower endomorphy and mesomorphy, while more linear physiques correlated with better bone parameters. Physique and type of exercise training appear to be associated with bone status. Both weight-bearing and non-weight bearing exercise improve calcaneus bone parameters such as BQI to different extents. It might be preferable to combine some weight-bearing exercise during the sessions, and it is also highly recommended after a competitive period and during recreational sport activities.


Introduction
Osteopenia and osteoporosis in males are becoming an increasingly important public health problem, and their prevalence in male patients is also high. Twenty percent of men over the age of 50 year will suffer an osteoporotic fracture during their lifetime [1,2].
Osteoporosis is about four times more common in women, but one in three patients with osteopenia (more frequent than osteoporosis) is a man [3].
Osteopenia associated with lower bone mass (new Volume 2(2): 2020 term of osteopenia is low bone mass) and lower bone density than in normal bone status. The treatment of osteopenia is complex, with an emphasis on developing a healthy lifestyle and most often medications are also recommended. Osteopenia is usually associated with no symptoms or pain, so it is often not diagnosed until after a fracture, that is why prevention is so important. Bone degeneration can be prevented, decreased or slowed down with regular physical activity. Cross-sectional studies have demonstrated greater bone mineral content and density in athletes [4,5,6,7,8]. Moreover, longitudinal studies confirm the beneficial effects of regular exercise on bone health [9,10]. In adults bone remodeling highly depends on the effective mechanical loading of stimuli. Weight-bearing activity has a beneficial effect on the skeleton through gravitational and muscular forces. Bones adapt to greater mechanical loading with adequate reconstruction in trabecular net and with higher density and thickness of the bone substance. Nonweight bearing activities have non-significant or little effect on bone density. Swimming and cycling are considered to be the types of physical activity that have low impact on bone density [11,12] however, they have a positive influence on other bone properties like elasticity and microstructure conforming by QUS [8]. Others reported divergent results in a study of male recreational athletes [13].
Cyclists, aged 20 to 59, were seven times more likely to have osteopenia in the spine than runners, controlled for age, body weight, and bone-loading history. According to a review it seems that cyclist's BMD correlates positively with the cumulative amount of bone loading forces experienced over their lifetime [14]. There is a negative correlation between bone mineral density and dermal calcium losses during exercise, also [14]. Bone density parameters increase in parallel with the level of mechanical loading and with the level of intensity of sport activities. It was found that athletes from different combat sports had higher BMD values than water polo athletes [15]. Running and ball games improve bone density [16]; and ultrasound bone parameters were higher in footballers than in swimmers, the latter group exceeded the values of the sedentary control group [17]. In several studies a positive osteogenic effect of different sports on bone density improvement has been detected with Dual-energy Xray Absorption (DXA) [4,7,15,18]. However, these DXA measurements give no suitable information as to other qualities of bone structure, such as elasticity, microarchitecture and fracture risk. Quantitative ultrasound measurement (QUS) provides information not only about bone mineral mass or density but also its quality parameters.
Some previous studies have analyzed somatotype differences in athletes. In a study was found that athletes in throwing events differed from other athletes [19] others found relationships between extreme ectomorphic constitution and performance in track and field athletes [20] and young Portuguese triathletes were considered mainly ectomorphic mesomorphs [21]. Carter and Heath analysed the somatotype differences between various Olympic and other sports participants [22]. In a study was found that elite water polo players belonged to the balanced mesomorph somatotype category [23].

Results
The basic statistics of anthropometric parameters of the subjects are shown in Table 1. Somatotype components differed significantly in the elite male athlete groups. Ectomorphy was the highest Volume 2(2): 2020     In terms of Bone Quality Index (Figure 4)
Because of the limited data regarding kayakers, we had to rely on the results of ten elite kayakers (six males, four females) [33]. A greater BMD was found in flatwater sprint kayakers than in controls in most upper body sites; total body' and lower body sites' BMD did not differ except for the pelvis. Strong correlations were found between BMD in upper body sites and lean body mass and body weight and fat percentage in controls. In contrast, we found a significant correlation between anthropometric and ultrasound bone parameters (SOS with mesomorphy; BUA with Bone%, Bone%/Muscle%; QUS with elbow, knee width) in the kayak-canoe subgroup.
Others investigated combat sport athletes and water polo players with DXA [15]. It was found that water polo players had significantly lower BMD, higher fat mass and did not differ from control individuals in these parameters, however, appendicular muscle mass was obviously higher in the athletes than in the controls. A similar trend was observed with the use of QUS in our comparison to other sports; even the mean of SOS and BQI in water polo players showed the lowest value, and the world leading water polo players could be characterized by a lower specific gravity.
In a Chinese study [17]  Correlations of somatotype and bone health should also be investigated in females. In addition, body proportions, primarily length and width dimensions of lower extremities, may also be associated with bone health.

Study limitations
The results of this study are limited due to its cross-

Conclusions
Our results suggest that the male elite athlete's type of sport activity with high mechanical loading on the skeleton may be an important factor in achieving a high peak bone mass and reducing the risk of ostepenia or osteoporosis later in life.
The training methods of non-weight bearing sports suggest that it might be preferable to include some weight-bearing exercise during the sessions, and it is also highly recommended after a competitive period and during recreational sport activities, as well.
Somatotype is a holistic approach of human body structure; so, its connection with local bone parameters requires further investigation either in athletes or in non-athletes.
Our results do provide relevance as to weight-and non-weight bearing exercise's impact on bone quality.
According to the authors, QUS is a sensitive enough method to reflect the difference in the effect of sportspecific loads (weight-bearing and non-weightbearing) on calcaneus bone. Both weight-bearing and non-weight bearing exercise improve calcaneus bone parameters such as BQI to different extents. It might be preferable to combine some weight-bearing exercise during the sessions, and it is also highly recommended after a competitive period and during recreational sport activities.
Funding: This research received no external funding.