In our study, we analyzed the condition of forearm bone tissue in men after SCI. The analysis concerned the impact on bone parameters in forearm: physical activity- wheelchair rugby training, body tissue components (fat mass and fat free mass), active smoking, age when the injury occurred, the period of injury. In our study, the frequency of low BMD among wheelchair rugby players was smaller than inactive men. In both groups of men after SCI, low BMD was particularly active in the proximal part of the forearm. Among wheelchair rugby players, smoking were the strongest factor reducing mean BMD. Condition of forearm bone tissue in men after SCI was has been studied before . The research focuses on the evaluation of BMD after SCI depending on the lifestyle, physical activity [10, 40], diet and supplementation . Studies have evaluated body composition in relation to BMD and BMC men after SCI [15, 42]. Often in study analyzed the determinants of fracture risk among individuals with spinal cord injury .
According to research bone loss after SCI occurs especially in the lower extremities. No significant changes in BMD after SCI were found in the proximal and distal forearm , radius , forearm . However at the same time higher values BMD was active men after SCI with performing upper extremity activities (e.g. wheelchair basketball) that men after SCI inactive . Goktepe et all.  compared the bone mineral density of elite paraplegic basketball players with the values obtained from their paraplegic sedentary counterparts. Wheelchair basketball in spinal cord-injured patients was associated with greater bone density in distal radius compared with sedentary paraplegics. Our research of wheelchair rugby players also showed better BMD compared to non-active men after SCI. A higher percentage with low BMD were among inactive men at both bone points by 36%.
Eloumi et al.  examined the effects of long-term rugby participation on bone mineral content (BMC) and density (BMD) of male rugby players and to determine if the diverse stimuli elicited by the actions of forwards and backs affect their skeleton differently. They showed that long-term rugby participation, starting at pubertal age, is associated with markedly increased BMC, BMD and bone size at all skeletal sites, except at the head. Similarly, in our study, men performed rugby training 5 years or longer and as analyses show had an effect on significantly better BMD than inactive men.
The musculo-skeletal adaptations, greater in forwards than in backs, could mimic training responses and therefore explain the bone features, localized in specific stressed regions. Sports training for people after spinal cord injuries is often the main factor to prevent the loss of BMD that occurs with age and due to immobilisation. Physical activity based on the intensive involvement of forearms significantly affected the better condition of bone tissue in this location. According to the theory of mechanostat, the effect of pressure forces generated by working muscles is local in nature, which explains the beneficial effect of the upper limbs driving a wheelchair on BMD in wheelchair rugby players. Rugby training also includes resistance exercises, which are an important element of beneficial bone loading .
Regular exercises, which load the skeleton with impact forces, are positively correlated with the mechanical bone strength. Athletes of sports characterized by high impact forces, such as rugby, have higher BMD than non-athletes . Participation in regular impact exercises is commonly suggested as a way to reduce the risk of osteoporosis at a later age . Most studies to date have suggested that resuming sports activities at a right time after treatment and rehabilitation is useful in preventing the loss of BMD in wheelchair athletes and can also affect their quality of life .
We know from general population studies about the negative impact of smoking on BMD. However, there are very few such studies involving men after SCI. In our study 40% of rugby players were smokers, which translated into the frequency of low BMD. A significant relationship (F = 8,7140; p = 0049) were found between mean BMD and smoking in active and inactive men after SCI. Smokers men had the lowest BMD values.
A meta-analysis conducted by Ward et al  showed that smokers had significantly reduced bone mass compared to non-smokers who had never smoked and those who had smoked in the past. BMD deficits were particularly evident in the hip, where the bone mass of smokers was one-third SD lower than in non-smokers. The adverse effects of smoking on the health of athletes are therefore wider than just the risk of lung cancer or poorer physical capacity. This topic requires more detailed research and analysis.
Studies have shown that BMD also depends on body composition . In the case of athletes, the fraction of tissue components in the body mass is closely related to the type of sport practiced, training routines, and training experience. In our study, most of the rugby players had a normal BMI or were overweight, which may have been caused by higher muscle mass. There were no cases of obesity among wheelchair players, which, as studies show, is a common occurrence in people after spinal cord injuries  and related to insufficient physical activity. In our study, there was no significant relationship of FFM with bone parameters. Previous studies have demonstrated the effect of body composition on BMD and BMC. Elite rugby players are characterized by body mass index (BMI) similar to that in obese people , but they differ significantly by their low fat content, high fat-free mass and frequent exposure of the skeleton to stress due to training. Studies suggest the key role of lean body mass in maintaining bone strength and resistance to fractures .
Despite the high number of injuries, rugby can be considered a sport that has a beneficial effect on BMD. Athletic training is associated with increased muscle strength. In our study, active men after SCI had a significantly better HGS score than inactive men. In addition, HGS had a significant effect on BMD dis. Previous studies have also shown that long-term practicing of rugby, from adolescence onwards, is associated with significant increases in BMC, BMD and bone size in numerous skeletal locations [42, 48]. Musculoskeletal adaptations represent a response to training loads. However, it is worth noting that smoking can limit the beneficial effect of sports training on bone health. Furthermore, studies have demonstrated that significant changes in body composition are observed at later stages of sports training. Increased fat mass and lower fat-free mass can have a negative effect on the power-to-weight ratio, and can therefore generate lower forces on the skeletal system .
This study makes an important contribution to this area of research. In men after SCI especially in physically active people who train regularly, early detection of the risk of low BMD allows to take effective prophylactic measures and reduce the risk of osteopenia, osteoporosis and consequent fractures. The major strength of the study is that a reliable and accurate research methodology was used. The research was conducted by a highly-qualified team with many years of research experience in the field. All data were collected using well selected and internationally recommended research tools. One of the study limitations is the relatively small yet sufficient size of the study group. It cannot provide a full representation of the population of men after SCI at this age. The body tissue composition was evaluated only by the anthropometric method, as it was impossible to perform bioelectrical impedance testing.