BIOMECHANICAL AND METABOLIC RESPONSES TO SEAT-TUBE ANGLE VARIATION DURING CYCLING IN TRI-ATHLETES

INTRODUCTION Triathlon is a recent, physically demanding sport and is divided in three different disciplines: swimming, cycling and running. Each of these disciplines is completely different from the other two and consequently muscle recruitment during these tasks is different. One of the most physically demanding part of this sport is the transition from one discipline to another, in particular from cycling to running [1]. Many tri-athletes believe that increasing seat-tube angle (STA) can bring advantages in the following running part [2]. The aim of the present study was to evaluate the effects of changing the STA from 73.5° to 78° on the metabolic response and on the muscle activation pattern, maintaining a controlled kinematic in order not to have changes due to a unusual cycling position. MATERIALS & METHODS Five healthy male volunteers (age 34±x years, height 1.74±x m and weight 70± kg) participated in this study. They all have experienced outdoor cycling at competitive level in the past and were well trained at the time of the tests. They were asked to cycle for 5 minutes in order to get an initial warming up. Subsequently, a sequence of maximal voluntary contraction (MVC) exercises were performed. All participants cycled at two different power levels, 230Watts and 300Watts (respectively with a gear ratio of 56/16 and 53/13) and with two different seat tube angles (73.5° and 78°) on a bike (RP3, Fondriest, Italy). Each combination of power level and STA was maintained for 3 minutes, during which the subject was asked not to stand up on the pedals and not to change position of hands. 3 minutes of rest were imposed between each trials. The test order was randomized in order to exclude fatiguing effects. Gas exchange data (Quark b2, Cosmed, Rome, Italy), kinematics (SmartD, BTS, Italy) and surface electromyography (EMG) (PocketEMG, BTS, Italy) were acquired during the tests. Surface EMG was measured from the following muscles of the right side of the body: soleus, medial gastrocnemius, vastus medialis, rectus femoris, gluteus, biceps femoris, tibialis anterioris and paravertebral muscles. EMG was rectified, filtered and normalized to MVC [3]. RESULTS No significant differences were found in Oxygen consumption and in respiratory exchange ratio (RER) between the two bike configuration used by the participants (STA 73.5° and 78°). Kinematic results showed no significant differences in hip, knee and ankle angles between the two different bike configuration (STA 73.5° and 78°) at both power level. Trunk-pelvis flexion extension angle was significantly constantly lower (-5°) with the steeper STA angle than with the shallow one. EMG results showed different activation amplitudes in muscles with the two STA configurations. The results showed the same trend in all the participants. Summarized EMG results are shown in Table 1. Table 1. Increment or decrement (mean ± standard deviation) in the muscle activation changing the STA from 73.5° to 78°. DISCUSSION Kinematic results showed no significant differences, confirming that the position maintained by the athletes in the two configurations were consistent with normal cycling. EMG results showed that biceps femoris, medial gastrocnemius and vastus medialis are less activated with the steeper STA than with the shallow one. With an increased STA, the athletes cycled with the seat over the crank centre, permitting to decrease the activation of some muscles, maintaining the same power output [4]. These results can bring advantages in the following running phase thanks to a minor muscle fatigue because a minor activation of the biceps femoris during the cycling phase in triathlon permits a better efficiency in the following running phase [1]: inferior muscle fatigue could let the athlete to have a longer and more efficient stride.