Table 3. Subjective feelings of endurance and exertion (1–10 point scales) after a graded exercise test, and perceived muscle power after a 15-s Wingate test with the administration of 3 mg/kg/day of caffeine or a placebo for 20 consecutive days.
| Perceived endurance | Perceived exertion | Perceived muscle power | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Day | Placebo | Caffeine | Effect size (±90% CI) |
Qualitative inference |
Placebo | Caffeine | Effect size (±90% CI) |
Qualitative inference |
Placebo | Caffeine | Effect size (±90% CI) |
Qualitative inference |
| 0 | 5.6±1.2 | 5.4±0.9 | -0.1(-0.6–0.4) | Unclear | 9.2±1.0 | 9.5±0.6 | 0.3(0–0.6) | Likely positive | 5.4±1.0 | 5.8±0.7 | 0.4(-0.1–0.9) | Possibly positive |
| 1 | 5.3±1.5 | 6.1±0.9*† | 0.5(0.1–1.0) | Likely positive | 9.4±1.1 | 9.4±0.8 | -0.1(-0.4–0.3) | Unclear | 5.7±1.6 | 6.4±0.7† | 0.3(-0.2–0.8) | Possibly positive |
| 4 | 5.7±1.1 | 5.9±1.0 | 0.2(-0.3–0.8) | Unclear | 9.4±0.8 | 9.5±0.7 | 0.1(-0.5–0.7) | Unclear | 6.0±0.7 | 6.2±1.1 | 0.0(-0.8–0.9) | Unclear |
| 6 | 5.9±0.9 | 5.8±0.9 | -0.1(-0.4–0.3) | Unclear | 9.5±0.7 | 9.6±0.7 | 0.1(-0.1–0.3) | Unlikely positive | 6.3±0.6 | 5.7±1.3 | -1.0(-2.2–0.2) | Unclear |
| 8 | 5.3±1.5 | 5.5±1.8 | 0.1(-0.5–0.7) | Unclear | 9.5±0.8 | 9.6±0.5 | 0.1(-0.3–0.5) | Possibly negative | 5.0±1.5 | 5.1±1.7 | 0.1(-0.5–0.7) | Unclear |
| 11 | 6.1±1.0 | 5.0±1.8 | -1.3(-3.0–0.3) | Unclear | 9.5±1.0 | 9.3±1.0 | -0.2(-1-0.6) | Unclear | 6.3±1.3 | 5.0±1.7 | -1.0(-2.3–0.2) | Unclear |
| 13 | 5.5±1.4 | 6.3±0.8†* | 0.5(0.1–0.9) | Likely positive | 9.7±0.5 | 9.6±0.7 | -0.2(-1.0–0.6) | Unclear | 6.2±1.2 | 6.2±1.5 | -0.1(-0.9–0.7) | Unclear |
| 15 | 5.8±1.5 | 6.2±0.9† | 0.2(0.3–0.8) | Unclear | 9.6±0.7 | 9.7±0.5 | 0.0(-0.6–0.6) | Unclear | 5.8±1.2 | 5.8±1.4 | 0.0(-0.8–0.8) | Unclear |
| 18 | 5.8±1.0 | 6.1±0.9† | 0.3(-0.2–0.8) | Possibly positive | 9.8±0.4 | 9.6±0.9 | 0.0(-0.4–0.3) | Unclear | 5.9±1.2 | 6.1±1.1 | 0.2(-0.4–0.7) | Unclear |
| 20 | 5.8±1.2 | 5.6±1.6 | -0.1(-0.7–0.4) | Unclear | 9.8±0.4 | 9.6±0.9 | -0.2(1.5–1.0) | Unclear | 5.7±0.0 | 6.3±0.9 | 0.6(-0.0–1.2) | Likely positive |
Note: All variables were assessed with 1–10 point scales where 1 point meant minimal amount of the variable and 10 points meant maximal amount of that variable (5 points was the value used to indicate not feeling any difference from a regular day). CI = confidence interval;
(*) Caffeine different from placebo for the same day, P < 0.05.
(†) Different from day “0” within the same treatment, P < 0.05.
Note: On days “0” and “11”, both the placebo and caffeine trials were performed without the administration of any capsule.