Lang geleden? Dat zeker! Het volgende stukje heeft dan ook veel tijd gekost. Maar nu kan ik het met de wereld delen. Ik heb deze keer gekozen voor een ‘argumentative essay’. Wat zeg je? Een wetenschappelijk betoog. De uitdaging is de volgende: schrijf en onderbouw een vernieuwende wetenschappelijke interventie, eentje die momenteel nog niet gebeurt en waarvan het nochtans duidelijk is dat het wél zou moeten gebeuren. Jahaa, dat vergt creativiteit! In 2004 flikte ik het al een keer. In BodyTalk nr.257 – een gezondheidsmagazine onder uitgave van VUB – introduceerde ik peperkoek als energiebron voor tijdens lange fietstochten. De wetenschappelijk wereld pikte het idee op en vandaag adviseert elke sportdiëtist de kruidige koek als ideale mengeling van snelle en trage koolhydraten. Baanbrekend werk, daar heb ik het dus over. Dit is weer zo’n poging. Deze keer wil ik jonge renners – voor wie mij kent is jeugdwielrennen een van mijn dada’s – behoeden voor een verzwakte botsterkte met alle gevolgen vandien op latere leeftijd. Zullen binnenkort alle renners dansen als onderdeel van hun dagelijkse training? Laat het me weten als je er eentje spot 😉

Adolescent road cyclists should incorporate daily spontaneous dancing to improve bone strength.

Introduction
Road cycling is a popular sport, also amongst the youngest. After the broadcast of a Tour de France stage, toddlers grab their small bikes to reenact the race they have just witnessed. It is cute to see them dream of becoming the future yellow jersey. As they reach the age of six, it is allowed to join a real cycling team and to compete in real road races. While maturing, the hours on the bike become gradually longer. Seventeen- to eighteen-year-old cyclists compete the junior category. Racing distance is about 140 km and therefore bike rides add up to a weekly total of about 600 km. At an average speed of 30 km/h that means they spend weekly twenty hours on their bike. Adding up the required resting and schoolwork, there is little to no room for other activities. Multiple health questions can arise on that lifestyle. One of those questions concerns the impact on bone strength.

At a first glance, bone strength seems to be an issue for the elderly. Bone fragility is a major cause of morbidity and economic burden (1, 2). However, the disease that surfaces in the elder years seems to develop in the first twenty years of life (3). Therefore, maintaining bone strength or even increasing it is critical in adolescence (1, 3). Aspects like bone mineral content, bone mineral density, bone mass, bone size, structure and microarchitecture account for bone strength and resistance against fracture (4). An increase of only three to five percent in bone mineral density is estimated to result in as much as twenty to thirty percent reduction in fracture risk (5). A ten percent increase of peak bone mass in childhood is estimated to reduce the risk of an osteoporotic fracture during adult life by fifty percent (5). Road cycling however seems to negatively impact bone strength and increases the risk of stress and fragility fractures, both while an athlete is actively competing and later in life (6). Key points in that negative impact are mainly the sports-specific biomechanics and the fact that cycling is a non-weight-bearing sports (2, 6, 16).

On top of the knowledge that hormones and dietary intake influences bone strength, it seems that bones adapt dynamically to mechanical demands (7). The ability of bone to adapt to mechanical loading is much greater during adolescence than after maturity (8). Specifically, interventions that involve jumps and direct turns improve bone mineral content, bone mineral density, and structural properties without side effects (5). Although resulting in minimal bone mass gains, these gains translate into disproportionate increases in bone strength tailored to the sites of the highest mechanical stress (2). To the best of our knowledge, jumps and direct turns are not incorporated in standard cycling training. Dancing to a fun song involves spontaneously the requested jumping and turning. In this essay, we contend that adolescent road cyclists should incorporate daily spontaneous dancing to improve bone strength in the hip, pelvis and femoral neck (9).

Bone strength
Bone structure serves four main physiological function: bones provide locomotion, protect the organs, form a reservoir for mineral storage and provide an environment for the development of hematopoietic cells (2, 7). Bone strength is dependent on several factors including the microarchitecture of its matrix components and its bone mineral content, its bone mineral density, but also its size, shape, and bone mass (7, 10, 11). Approximately forty to sixty percent of adult bone mass is achieved during adolescence. Peak bone mass – determining our fracture risk for the rest of our lives – is usually reached by the end of the second decade of life (1, 9, 12). After that age, bone loss is inevitable (7) and fraction risk increases (5).

Influence of physical activity
Peak bone mass is dependent on five main factors: sex, race, hormones, nutrition, and physical activity. While the first two factors are nonmodifiable and hormones are barely, nutrition and physical activity are manageable (3, 7). Within the domain of physical activity, especially weight-bearing (1) and impact loading of the skeleton seem to adapt bone strength (3). This adaptation prevents fracturing under peak loads (3). The key element of this so called mechanostat is the sensing of the loading (7, 11). Bone cells respond specifically to the magnitude and the direction of the strain when a bone is under load. Also, the rate of strain development, the duration and the repetition of the loading are of influence (13, 14). Bones are much more adaptable to mechanical loading during adolescence (8). To put it concisely, bone strength is adaptable in adolescence and weight-bearing plus impact loading are key.

Road cycling and bone strength
Road cyclists often have a lower bone mineral density than athletes participating in other sports, sometimes even lower than their inactive peers (6, 9). Over a twelve-month training period, road cyclists lose approximately 1.5% of bone mass at the hip (15). More specifically, cycling performed throughout adolescence may compromise the acquisition of peak bone mass (9). Adolescent cyclists have lower bone mineral content and bone mineral density compared with healthy age-matched controls in regions of clinical interest like the hip, pelvis and femoral neck (9). The reasoning for this is thought to be multiple. For starters, cycling is a non-weight-bearing sport. On the bike, body weight is supported by the saddle and the handlebar. Participants in non-weight-bearing sports have been shown to have lower bone mineral density (6). Furthermore, cyclists lay down a lot in recovery. Disuse of the skeleton and prolonged bed rest promote bone mass reduction (2, 16). Secondly, while road cycling, ground reaction forces are absent (6). Looking deeper into the biomechanics, the cycling movement is regular, uniplanar and high-frequency thus with fast load-relax cycles. Extrapolating what is known about the effect of load characteristics on bone formation in animal studies, it seems that the cycling movements are less effective in building bone mass than the high-impact, irregular, multiplanar loads with a slower load-relax cycle (6). Thirdly, as the cycling movement is inherently repetitious, there are no brief periods of rest in between. Recovery periods of as little as 14 seconds between load cycles have been shown to improve bone formation compared with more frequent load cycles (6). In summary, road cycling performed throughout adolescence impacts negatively on bone strength, which increases the risk of fractures (5).

Bone strength training
Interventions during adolescence that involve jumps and direct turns improve bone mineral content, bone mineral density, and structural properties without side effects (5). Bone strength at the loaded skeletal sites will thereby be improved  by one to eight percent (17). Workouts where ground impact forces are transmitted through the bones in multiple planes and at varying intervals with brief periods of rest in between (6) lead to increased bone parameters over six months (7). Moreover, these effects are maintained in time after the intervention has ended (5). The intended movements can be found in plyometric jumps, two-footed drop jumps or multidirectional hops, but more intuitively in ball games, rope skipping, step aerobics or dancing (2, 5, 18). Either ten-minute interventions twice a week or three-minute interventions three times a day and five days a week seem enough to improve bone strength (5).Because both protocols result equally, the three times three minutes a day is favorable (5). Furthermore, because similar results were found independently of the type of jumping intervention, it is encouraged to search for the most enjoyable exercise (5). Freestyle dancing over a fun song seems to have all the ingredients to increase bone strength: the song thus the exercise lasts approximately three minutes and contains spontaneously multiplanar high-impact jumping and turning with slow load-relax moments in between. On top of that, the areas where cyclists tend to have a lower bone strength are involved (9).

Feasibility
Implementing the advised scheme is not time-consuming. The length of a song and therefore a training session being no more than three minutes, it is a feasible addition to the training days. Moreover, the fun factor of the intervention will ensure that it will not feel as an extra duty on top of the already large weekly training load. Dance moments can be incorporated to start the morning with a happy feeling, anywhere and anytime during daytime, as a warm-up for the bike training and as a welcome interlude during studying.

Conclusion
Road cycling performed throughout adolescence impacts negatively on bone strength. This drawback increases the risk of fractures, both while an athlete is actively competing and later in life. However, bone strength is adaptable in the adolescent age range. Especially weight-bearing and impact loading of the skeleton seem to positively influence that adaptation. A regime of three times a day doing three minutes of jumping and turning in multiple planes, at varying intervals and with brief periods of rest in between seems ideal. Adolescent road cyclists should therefore incorporate three moments of spontaneous dancing in their daily training schedule to improve bone strength.

References

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