Change in total hemoglobin (ΔTHb) at: (a) the right and (b) the left trapezius muscle. AUC: area under the curve. MAX 1~MAX 3: the trapezius muscles contract with maximum effort for 1 min. Relax 1~Relax 3: the trapezius muscles relax for 2 min. Values are presented as mean, SE. †, different from the ΔTHb first rest (p < 0.05). *, **, different from the ΔTHb of the control group (p < 0.05, p < 0.01).