Physiological and electromyographic responses during 40-km cycling time trial: relationship to muscle coordination and performance.

The purpose of this study was to compare the oxygen uptake (VO(2)), respiratory exchange ratio (RER), cadence and muscle activity during cycling a 40-km time trial (TT), and to analyse the relationship between muscle activity and power output (PO). Eight triathletes cycled a 40-km TT on their own bicycles, which were mounted on a stationary cycle simulator. The VO(2), RER and muscle activity (electromyography, EMG) from tibialis anterior (TA), gastrocnemius medialis (GA), biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL) of the lower limb were collected. The PO was recorded from the cycle simulator. The data were collected at the 3rd, 10th, 20th, 30th and 38th km. The root mean square envelope (RMS) of EMG was calculated. The VO(2) and PO presented a significant increase at the 38th km (45.23+/-8.35 ml kg min(-1) and 107+/-7.11% of mean PO of 40-km, respectively) compared to the 3rd km (38.12+/-5.98 ml kg min(-1) and 92+/-8.30% of mean PO of 40-km, respectively). There were no significant changes in cadence and RER throughout the TT. The VL was the only muscle that presented significant increases in the RMS at the 10th km (22.56+/-3.05% max), 20th km (23.64+/-2.52% max), 30th km (25.27+/-3.00% max), and 38th km (26.28+/-3.57%max) when compared to the 3rd km (21.03+/-1.88%max). The RMS of VL and RF presented a strong relationship to PO (r=0.89 and 0.86, respectively, p<0.05). The muscular steady state reported for cycling a 30-min TT seems to occur in the 40-km TT, for almost all assessed muscles, probably in attempt to avoid premature muscle fatigue.

Effective force and economy of triathletes and cyclists.

The effective force applied on the crank, the index of pedalling effectiveness, and the economy of movement at 60, 75, 90, and 105 rev/min cadences were examined in nine cyclists and eight triathletes. Tests were performed on two days. Maximal oxygen uptake was measured and the second ventilatory threshold was estimated on day 1 using a stationary bicycle. On day 2, the four different cadences were tested at about 5% below the second ventilatory threshold. A strain gauge instrumented clip-less pedal mounted on the bicycle enabled us to measure the normal and tangential forces exerted on the pedal, while the pedal and crank angles were monitored with the aid of a video system. Based on this information, the effective force and the index of pedalling effectiveness were calculated. Cyclists produced significantly more effective force and a higher index of pedalling effectiveness at 60 and 75 rev/min and were significantly more economic at all cadences than triathletes. The significant and positive correlation between effective force and economy at all cadences suggests that improvement of the effective force would reflect on economy.

Análise de exercícios abdominais: um estudo biomecânico e eletromiográfico / Analysis of abdominal exercises: a biomechanical and electromyographic study

Na primeira parte deste trabalho foram determinados os potenciais de açäo muscular (PAM) do reto femoral (N=10) e das regiöes supre-umbilical (N=16) e infra-umbilical (N=13) do reto abdominal de estudantes de educaçäo física, durante a execuçäo de doze exercícios selecionados. Foram utilizados eletrodos de superfície conectados a um fisiógrafo. Analíses de variância com seus respectivos testes de significancia levaram às seguintes conclusöes: (1) que flexionar ou estender os joelhos, bem como fixar ou näo os pés näo alterou significativamente os PAM obtidos para as regiöes supra e infra-abdominal; (2) que a dificuldade verificada nos exercícios realizados em prancha inclinada era devida, em grande parte, à intensa atividade dos flexores do quadril e näo propriamente dos abdominais; (3) oito exercícios obtiveram PAM equivalentes àqueles obtidos pelos exercícios na prancha inclinada para as regiöes supra e infra-abdominal; (4) que os exercícios "canivete" e elevaçäo dos membros (com o executante suspenso em um espaldar sueco) exigiram simultaneamente grande intensidade das duas porçöes do reto abdominal e do reto femoral. Na segunda parte, o trabalho discute, inicialmente, fundamentos da biomecânica de alguns exercícios abdominais para, a seguir, ilustrar, através de traçados eletromiográficos, aspectos como: (a) a contribuiçäo das regiöes supra e infra-umbilical durante a execuçäo de determinados exercícios; (b) a repercussäo do encaixe de quadril no PAM do reto abdominal; (c) a realizaçäo de movimentos do tronco partindo da posiçäo em pé e (d) os PAM registrados nas fases concêntrica e excêntrica lenta de um exercício