Cardio-respiratory and neuromuscular responses to motocross race

Abstract

Tomi Konttinen. 2005. Cardio-respiratory and neuromuscular responses to motocrossrace. Department of Biology of Physical Activity. University of Jyväskylä. 37p.Objectives - The primary aim of the present study was to examine physiological andneuromuscular responses during motocross racing. Furthermore, maximal isometricforce levels of the upper and lower body were studied.Methods - Seven Finnish A-level (group A) and five hobby-class (group H)motocross-riders performed a 30 minute riding test at a motocross track and muscleforce and maximal oxygen uptake (VO2max) tests in a laboratory. Variablesdescribing cardio-respiratory strain were measured continuously during the riding andin the VO2max tests. Muscle activity using surface EMG recording was recordedduring the riding test and during the maximal isometric contractions.Results – During the race the mean VO2 reduced significantly in group A from 86 ± 10% to 69 ± 6 % of the maximum. In group H the reduction occurred from 94 ± 25 % to82 ± 20 %. The relative VO2 between the maximum and the riding test correlatedsignificantly with riding speed (r = 0.70, p < 0.01). Heart rate (HR) was maintainedcontinuously at the level of 97 ± 7 % of its maximum in group A and at 98 ± 3 % ingroup H. During the ride, the mean blood lactate concentration was 4.0 ± 1.0 mmol·l-1in group A but in group H it reduced from 5.7 ± 1.0 mmol·l-1 to 4.6 ± 0.7 mmol·l-1.Mean muscle activation of the lower body during riding varied between 24 – 38 % ofits maximum in group A and between 40 – 45 % in group H. The activation of theupper body muscles varied between 62 – 116 % in group A and 68 – 178 % in groupH of its maximum. The post-riding force measurements showed more significant(p<0,05) reductions in maximal voluntary contraction (MVC) of group H than MVCof group A. The absolute MVC measured before and after the riding experimentshowed greatest reductions in hand grip forces.Conclusions – Motocross causes great physical stress demanding on both skill andphysical capacity of the rider. Physical stress occurs due to handling of the bike whilereceiving continuous impacts, while muscle actions are both dynamic and isometricplacing demands in both aerobic and anaerobic metabolism. The data suggests thatboth the maximal capacity and the strain during the ride should be measured toanalyze the true physiological demands of motocross ride including the recording offorce levels before and after the ride to evaluate the neuromuscular fatigue due to therace.