Sport Sciences Research Institute Studies in Sport Medicine 2322-1658 14 33 2022 11 22 Comparison of co-contraction and peak contraction of selected lower limb muscles during landing on different surfaces in Block defense skills Comparison of co-contraction and peak contraction of selected lower limb muscles during landing on different surfaces in Block defense skills 81 96 3247 10.22089/smj.2022.12460.1590 FA Saba Abrifam PhD student from Islamic Azad University, Central Tehran Branch Ali Fatahi Assistant Professor, Sports Biomechanics Department, Physical Education and Sports Sciences Faculty, Islamic Azad University of Central Tehran Branch, Tehran, Iran 0000-0002-8863-4061 Hasan Matin Homaei Department of sport Physiology Journal Article 2022 04 17 Surface stiffness is a factor affecting the injuries since any change in in the amount of this parameter leads to the increased applied forces. This is a quasi-experimental, causal-comparative, and applied study. The statistical population included 14 volleyball players aged between 18 and 20. The muscles’ electrical activity was recorded by an 8-channel electromyograph based on the SENIAM protocol (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles) on four selected muscles of the lower limb. Mean and standard deviation (SD) were employed for data description, Shapiro-Wilk test for the assessment of data distribution normality, analysis of variance with repeated measures for the effect of surface type on the research variables, and Bonferroni post hoc test was used for the assessment of differences. Furthermore, the repeated measurement test’s results revealed no significant difference between groups in terms of the peak muscle activities in Vastus lateralis muscle and Biceps femoris muscle when jumping and landing on tatami, grass, and sand (p≤0.05); however, the surfaces were significantly different in the tibialis anterior muscle and gastrocnemius muscle (p = 0.00). Besides, there was no significant difference between co-contractions in knee and ankle joint (p≤0.05); the difference was that in the knee joint, the highest average co-contraction was seen on the grass and its lowest rate on the sand, while in the ankle joint, the lowest rate was seen on the sand and the highest rate on tatami. Surface stiffness is a factor affecting the injuries since any change in in the amount of this parameter leads to the increased applied forces. This is a quasi-experimental, causal-comparative, and applied study. The statistical population included 14 volleyball players aged between 18 and 20. The muscles’ electrical activity was recorded by an 8-channel electromyograph based on the SENIAM protocol (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles) on four selected muscles of the lower limb. Mean and standard deviation (SD) were employed for data description, Shapiro-Wilk test for the assessment of data distribution normality, analysis of variance with repeated measures for the effect of surface type on the research variables, and Bonferroni post hoc test was used for the assessment of differences. Furthermore, the repeated measurement test’s results revealed no significant difference between groups in terms of the peak muscle activities in Vastus lateralis muscle and Biceps femoris muscle when jumping and landing on tatami, grass, and sand (p≤0.05); however, the surfaces were significantly different in the tibialis anterior muscle and gastrocnemius muscle (p = 0.00). Besides, there was no significant difference between co-contractions in knee and ankle joint (p≤0.05); the difference was that in the knee joint, the highest average co-contraction was seen on the grass and its lowest rate on the sand, while in the ankle joint, the lowest rate was seen on the sand and the highest rate on tatami. https://smj.ssrc.ac.ir/article_3247_ac45088df2e8d3cd2d8fbafceb920878.pdf