Background Knee valgus is associated with non-contact anterior cruciate ligament rupture and this injury commonly occurs at the end of competition and/or training sessions. Probably, muscle fatigue is associated to this injury occurrence. Clinically, knee valgus is easily identified by the quantification of frontal plane knee projection angle (FPKPA).

Objective The purpose of this study was to compare FPKPA before and after a maximal, incremental shuttle-run testing protocol used to induce fatigue in elite male volleyball athletes.

Design Cross-sectional study.

Setting Sports Sciences Laboratory at the Universidade Federal de Minas Gerais.

Patients (or Participants) Thirteen elite male volleyball athletes with a mean age of 27.69 (+7.85) years, body mass of 92.00 (+8.97) kilograms and height of 1.94 (0.06) meters participated in a preseason assessment.

Interventions (or Assessment of Risk Factors) Fatigue was induced by performing a maximal-incremental shuttle-run test for the estimation of maximal aerobic power according to the protocol proposed by Ramsbotton et al. (1988).

Main Outcome Measurements FPKPA was measured during single-leg squat and involved a line connecting antero-superior iliac spine, a middle point between knee condyles and a middle point between the malleolus. The athletes performed 3 single-leg squats and a mean of the 3 FPKPA on the dominant lower limb was analyzed.

Results The dominant lower limb had a mean FPKPA of 3,18 o (±4.23) prior to and a mean FPKPA of 3.73 o (±4.03) after the fatigue protocol. A Studen's t-test analysis showed a statistical significant difference (p=0.019; mean difference=3.18; IC 95% of 0.62–5.74).

Conclusions Elite male volleyball athletes had higher values of FPKPA on the dominant lower limb after a maximal, progressive exercise leading to fatigue. Probably, elite volleyball players may be under a higher risk of muscle-skeletal injuries under muscle fatigue conditions.