Fig. 30.1
Cervical sub-region (a) chosen for DXA measurements (b)
With DXA, the least detectable mass is 250 g. The accuracy rate is 2 % for a reproducibility of ± 200 g for the members and of ± 450 g for the thorax.
Effective X-ray dose for a whole-body scan is only 8.4 μSv.
Dynamic calibration is integrated into the measurement procedure.
DXA cannot measure hydration status but is robust with respect to variations in lean mass hydration. Hologic Inc. takes into account a constant coefficient of hydration of the lean mass of 73.2 % which little influences the measurement of fat mass and lean mass.
30.2.3 Follow-Up of the Indices (Fig. 30.2)
For each player, the three compartmental trend was monitored by colored visual mapping and by diagrams of follow-up over time.
Fig. 30.2
Individual follow-up for body fat distribution (a) and fat mass/lean mass indices (b)
This type of monitoring can emphasize the variations of fat mass and lean mass in the trunk and the limbs (percent fat, fat mass ratio, lean mass ratio).
Polygonal diagrams are very attractive to show the individual profile of the player for separation of fat mass and lean mass with four indications of percent mass for legs, arms, trunk and abdomen.
30.3 Results
Table 30.1 describes the baseline characteristics of the cohort at the start of the study for all the players: age, weight, height, BMI.
Table 30.1
Baseline characteristics for the cohort at the beginning of the study
Table 1 (n = 38) | Forwards (n = 21) | Backs (n = 17) |
|---|---|---|
Characteristics | ||
Mean age (years) | 25 | 26.8 |
Mean height (cm) | 190.5 | 182.8 |
Mean weight (kg) | 116.5 | 93.8 |
Mean BMI (kg/m2) | 32.2 | 27.9 |
Table 30.2 describes the ratios for all the players at the start of the study: fat mass percent, fat mass/height2, lean mass/height2, appendicular lean mass/height2. SD for lean mass/height2 is also shown by player position, i.e. forwards and backs.
Table 30.2
Baseline ratios for the cohort at the beginning of the study
Table 2 (n = 38) | Forwards (n = 21) | Backs (n = 17) |
|---|---|---|
Characteristics | ||
Fat mass ratio (percent fat) | 20.1 | 15.3 |
Fat mass/height2 | 6.5 | 4.3 |
Lean mass/height2 | 24.9 | 23.5 |
Appendicular lean mass/height2 | 13.5 | 11.5 |
Figure 30.2 shows the indicial individual follow-up for players.
Figure 30.3 shows the case of a cervical sprain (hyperflexion) followed by MRI and DXA for 3 weeks. In that 3 weeks:
total body lean mass + bone mass decreased 2.79 %;
lean mass/height2 changed from 20.5 to 20, appendicular lean mass/height2 changed from 10.1 to 9.75;
total body percent fat increased from 12.6 to 12.8 (1.58 %);
analysis of cervical sub regions showed no significant variation for percent fat whereas the total cervical lean mass +bone mass increased 4.27 %.
Fig. 30.3
Cervical sprain between the spinous processes of the first and second thoracic vertebrae. Sagittal (a) and axial (b) STIR MRI shows interspinous ligament tear and edema seen as a hyperintensity signal. Detailed DXA measurements with cervical sub-region R1 and R2 (c)
30.4 Discussion
30.4.1 Specificity of the Rugby Player
For a man of medium corpulence, the fat-mass ratio (total body fat-mass ratio) is between 15 and 20, and the lean-mass ratio between 35 and 40.
According to the data of the World Health Organization [17], the normal BMI (body mass index) is between 18.5 and 25 kg/m2. In reality most of the rugby players have a BMI beyond 25 kg/m2 without being overweight or obese.
Thus, we shall insist on using fat mass/height2 and lean mass/height2 ratios, the only indices that are really adapted to the follow-up of rugby players.
Another dilemma is the antagonism between the protecting mass, fat and lean, and the performance/weight ratio. In many sports it is considered and proved that carrying excess body fat can reduce performance because of the weight overload and slower performance. On the other hand, higher subcutaneous fat is also considered protection against injury [18]. The “airbag” represented by fat and muscles protects the human body.
A comparative analysis of mass distribution by player post is also interesting [13]. According to the literature, height, weight, percent fat mass and BMI are higher in forwards than backs. Our Tables 30.1 and 30.2 confirm this fact, and also that the ratios for fat mass and lean mass are both higher in forwards.
30.4.2 Importance of the Follow-Up in the Change of Lean-Mass Composition [14, 19, 20]
The ideal times for DXA follow-up of rugby players for our purposes would include each of the three phases of the competitive season: pre-season (August or September), mid-season (January or February), and post-season (June or July).
In reality this ideal is quite impossible because of the busy schedules of the teams.
Georgeson et al [14] studied three-compartment body changes and tried to determine their relationship to injury.
Does body composition change across a 12-month period in response to pre-season training, seasonal game play and off-season rest? Is pre-season body composition (bone, muscle and fat) related to injury incidence throughout the season? Are changes in body composition during the playing season related to incidence of injuries?
We asked these questions and found that professional rugby league players tend to lose lean mass across a playing season but regain it with pre-season training. No gain for fat mass was found in this study.
BMD increased until mid-season and decreased thereafter.
No strong relationships were detected between anthropometric characteristics and incidence of injury. Georgeson et al however questioned whether reductions in lean mass might reduce muscle strength and endurance, speed, agility and power across the course of the season.
Harley et al [20] noticed that between the beginning and midpoint of the season, bone mass, fat mass, lean mass and per cent fat showed no significant change. BMC however increased significantly.
Between mid-season and post-season, bone mass and BMC showed no significant change, although significant changes were observed in lean mass (-1.54 %), fat mass (+4.09 %), and percent fat (+4.98 %).
The significant changes in body composition seen over the latter stages of the competitive season may have implications for performance capabilities at this important stage of competition. An increase in fat mass and decrease in lean mass may have a negative effect on the power/bone mass ratio, and therefore may be a cause for concern for playing, coaching, and medical staff. Coaching and strength and conditioning staff should prescribe appropriate training and nutritional practices with the aim of maintaining the players’ optimal body composition until the conclusion of the competitive season, so that performance capabilities are maximized over the entire competition period.
Because lean mass (muscular mass) is the real provider of strength for the athlete, we think that the lean mass/height2 ratio and the appendicular lean mass/height2 ratio seem to be the best indices for the study of skeletal muscular mass.
The frequency of lower limb injuries is high, so we want to insist on the importance of the assessment of lower-limb volumes [21], but the comparison with upper limbs and the search for any asymmetry should also be considered
We also believe that the age-related decrease in muscle mass and function, known as sarcopenia [6] is correlated with functional limitation and frailty.
Moreover we know that satellite promyoblastic cells [22] are naturally present in all the skeletal muscles, but that their density in muscles decreases with the age.
The wounded muscle can regenerate from the easily actionable satellite cells by creating new muscular fibers. The production of cytokines facilitates the repair.
Related posts:
Muscle Physiology in Athletes
Therapeutic Alternatives: Principles and Results
Abdominal Wall Injuries
Functional Anatomy of the Muscle
Gluteus Maximus and Surrounding Muscles Injuries
General Considerations on Muscle Denervation in Sports Activities: Shoulder Entrapment Syndromes and Compressive Neuropathies
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