Hamidreza Barzegarpoor, Hamid Rajabi, Saied Mohammadi, Rana Fayazmilani,
Volume 0, Issue 0 (11-2019)
Abstract
Performing a mental exertion during an exercise increase fatigue indices and the amount of fatigue seems to depend on the type of mental exertion. So, the purpose of the present study is comparing the effects of performing types of mental exertion during cycling exercise on fatigue indicators. Methods: 10 cyclist men with average peak power output 236 ± 36 W invited for 5 different sessions. In the first session, anthropometric characteristics and of cycling peak power output (PPO) have determined. In the next four sessions, cycling for 45-min at 65% PPO on the cycle ergometer with (Stroop, AX-CPT and PVT) or without mental exertion. Rate of perceived exertion (RPE) and heart rate were recorded while cycling every 10 min and cortisol concentration was measured before and 30 min after exercise finished. Two-way repeated-measures ANOVAs were used to analyzing data. Results: Performing 45 minutes of Stroop mental exertion during cycling exercise increased RPE and cortisol concentration compared to cycling exercise alone (P˂0/05) but there is no differences between AX-CPT and PVT to cycling exercise alone. Conclusion: The results of the present study showed that performing Stroop mental exertion during the cycling exercise than cycling exercise alone increase more the fatigue indices.
Dr. Leila Ghazaleh, Mis Fahimeh Bakhshizadeh, Dr. Rana Fayazmilani,
Volume 19, Issue 21 (9-2021)
Abstract
It is necessary to examine the changes of muscle co-contraction in different percent of fatigue-induced force reduction. The present study aims to investigate the effect of fatigue-induced force reduction of knee extension on muscle co-contraction. Ten healthy and active women aged 26.10±2.99 years performed fatigue protocol including 5 seconds of maximal voluntary isometric contraction (MVIC) of the knee extension and a 5-second rest. Muscle co-contraction was calculated for each subject in the repetitions in which the MVIC force was reduced by 10, 20, 30, 40 and 50% as compared to the pre-fatigue MVIC force. Knee extension force and muscle activity measured by Isokinetic and electromyography apparatus, respectively. The difference between co-contraction of vastus lateralis and medialis in different percentages of force reduction was not statistically significant. The co-contraction of rectus femoris and biceps femoris increased by 40 and 50% of force reduction compared to pre-fatigue co-contraction (P<0.01). Co-contraction of biceps femoris and vastus lateralis increased by 20, 30, and 40%, as well as co-contraction of biceps femoris and vastus medialis increased 40% of the force reduction, compared to pre-fatigue co-contraction (P <0.05). The results, overall, showed that the change of co-contraction during fatigue is influenced by the selected muscle and the rate of force reduction. This finding can help researchers decide how neuromuscular fatigue effects on muscle co-contraction
