Acute molecular responses to lengthening vs shortening muscle contractions

To help elucidate mechanistic differences between lengthening and shortening muscle contractions we compared changes in gene expression within 24 h of an acute bout of each type of contraction in the quadriceps. Three healthy young men performed shortening contractions with one leg while the contralateral leg performed lengthening contractions. Biopsies were taken from both legs before exercise, 3, 6, and 24 h afterwards. Expression profiling was performed using a custom-made Affymetrix MuscleChip containing probesets of approximately 3,300 known genes and ESTs expressed in skeletal muscle. We identified 49 genes differentially regulated between the lengthening and shortening contractions. Using unsupervised hierarchical clustering, we identified four distinct clusters, three of which corresponded to unique functional categories (protein synthesis, stress response/early growth, and sarcolemmal structure). The results suggest distinct molecular pathways as early as 3 h post exercise. The molecular differences might contribute to mechanisms underlying the physiological adaptations seen with training using the two modes of exercise. Keywords: Time Series Design The hypothesis of the current study was that genes involved in hypertrophy will be differentially regulated between the two types of contractions.