Table 2.
Simple linear regression between male participant characteristics (independent variables) and serum testosterone concentrations as the dependent variable
| Independent variables | Values | Dependent variable: serum testosterone (nmol/L) | |||
| All (n=27)* | β | SE | P value | 95% CI for β | |
| Age (years) | 24.2 (17.1–30.0) | −0.321 | 0.100 | 0.110 | −0.371; 0.040 |
| Body weight (kg) | 74.4±12.4 | 0.125 | 0.099 | 0.542 | −0.143; 0.265 |
| DXA FFM (kg) | 61.1±8.6 | 0.299 | 0.137 | 0.138 | −0.073; 0.491 |
| DXA FFM% (FFM/BW) | 82.6±4.3 | 0.340 | 0.268 | 0.089 | −0.078; 1.030 |
| DXA fat% | 13.5±4.2 | −0.342 | 0.273 | 0.087 | −1.052; 0.076 |
| Total body BMD Z-score | 1.0±1.2 | 0.052 | 1.077 | 0.803 | −1.950; 2.494 |
| RMR (kcal) | 2030±285 | 0.259 | 0.005 | 0.284 | −0.005; 0.015 |
| RMR/FFM (kcal/kg) | 33.6±4.9 | −0.073 | 0.287 | 0.765 | −0.694; 0.519 |
| Ferritin (μg/L) | 91 (52–146) | −0.085 | 0.015 | 0.679 | −0.036; 0.024 |
| Fe (μmol/L) | 19.2±8.0 | 0.421 | 0.137 | 0.032 | 0.029; 0.596 |
| TIBC (μmol/L) | 53.6±6.9 | −0.440 | 0.158 | 0.025 | −0.703; −0.053 |
| TSH (mU/L) | 2.3 (1.5–3.5) | 0.187 | 0.956 | 0.360 | −1.08; 2.864 |
| IgA (g/L) | 2.1 (1.3–2.6) | −0.193 | 1.513 | 0.345 | −4.582; 1.665 |
| Dizziness score† | 0.0 [0.0–1.0) | 0.125 | 0.738 | 0.542 | −1.067; 1.979 |
| GI score† | 1.0 (0.0–2.0) | 0.183 | 0.915 | 0.372 | −1.056; 2.722 |
| Thermoregulation score† | 0.0 (0.0–2.0) | 0.240 | 0.689 | 0.238 | −0.588; 2.256 |
| Fatigue score† | 3.0 (1.0–5.0) | 0.218 | 0.330 | 0.284 | −0.320; 1.044 |
| Fitness score† | 5.0 (3.0–7.0) | 0.224 | 0.360 | 0.270 | −0.337; 1.148 |
| Sleep score† | 3.0 (1.0–7.0) | 0.138 | 0.350 | 0.502 | −0.483; 0.960 |
| Recovery score† | 2.0 (1.0–4.0) | 0.010 | 0.563 | 0.962 | −1.135; 1.189 |
| Energy level* score† | 3.0 (1.0–4.0) | 0.309 | 0.518 | 0.125 | −0.246; 1.891 |
Characteristics are presented as medians with IQRs (25th and 75th percentiles) for non-parametric and means±SD for parametric data.
*Characteristics for all male participants (n=27), of which all but one had a valid measure of testosterone.
†Scores derived from the Low Energy Availability in Male Questionnaire.
BMD, bone mineral density; BW, body weight; DXA, dual-energy X-ray absorptiometry; Fe, iron; FFM, fat-free mass; GI, gastrointestinal; IgA, Immunoglobulin A; RMR, resting metabolic rate; TIBC, total iron-binding capacity; TSH, thyroid-stimulating hormone.