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The aim of the present study was to establish the behavior of human medial gastrocnemius (GM) muscle fascicles during stair negotiation. Ten healthy male subjects performed normal stair ascent and descent at their own comfortable speed on a standard-dimension four-step staircase with embedded force platforms in each step. Kinematic, kinetic, and electromyographic data of the lower limbs were collected. Real-time ultrasound scanning was used to determine GM muscle fascicle length changes. Musculotendon complex (MTC) length changes were estimated from ankle and knee joint kinematics. The GM muscle was mainly active during the push-off phase in stair ascent, and the muscle fascicles contracted nearly isometrically. The GM muscle was mainly active during the touch-down phase of stair descent where the MTC was lengthened; however, the GM muscle fascicles shortened by approximately 7 mm. These findings show that the behavior and function of GM muscle fascicles in stair negotiation is different from that expected on the basis of length changes of the MTC as derived from joint kinematics.

Ruiter, C. J. de, M. D. de Boer, M. Spanjaard, and A. de Haan. Knee angle-dependent oxygen consumption during isometric contractions of the knee extensors determined with near-infrared spectroscopy. J Appl Physiol 99: 579 -586, 2005. First published March 17, 2005; doi:10.1152/japplphysiol.01420.2004.-Fatigue resistance of knee extensor muscles is higher during voluntary isometric contractions at short compared with longer muscle lengths. In the present study we hypothesized that this would be due to lower energy consumption at short muscle lengths. Ten healthy male subjects performed isometric contractions with the knee extensor muscles at a 30, 60, and 90°knee angle (full extension ϭ 0°). At each angle, muscle oxygen consumption (mV O2) of the rectus femoris, vastus lateralis, and vastus medialis muscle was obtained with near-infrared spectroscopy. mV O2 was measured during maximal isometric contractions and during contractions at 10, 30, and 50% of maximal torque capacity. During all contractions, blood flow to the muscle was occluded with a pressure cuff (450 mmHg). mV O2 significantly (P Ͻ 0.05) increased with torque and at all torque levels, and for each of the three muscles mV O2 was significantly lower at 30°compared with 60°a nd 90°and mV O2 was similar (P Ͼ 0.05) at 60°and 90°. Across all torque levels, average (Ϯ SD) mV O2 at the 30°angle for vastus medialis, rectus femoris, and vastus lateralis, respectively, was 70.0 Ϯ 10.4, 72.2 Ϯ 12.7, and 75.9 Ϯ 8.0% of the average mV O2 obtained for each torque at 60 and 90°. In conclusion, oxygen consumption of the knee extensors was significantly lower during isometric contractions at the 30°than at the 60°and 90°knee angle, which probably contributes to the previously reported longer duration of sustained isometric contractions at relatively short muscle lengths. energy utilization; submaximal isometric contractions; voluntary activation; fatigue TIME TO FORCE FAILURE DURING a single voluntary submaximal isometric muscle contraction is inversely related to knee extensor muscle length (16,21,26,31). Apparently, submaximal isometric contractions are less fatiguing at short muscle lengths compared with isometric contractions made at the same relative torque level but at longer muscle lengths. For tibialis anterior muscle it has been suggested (13) that the cause for the lower fatigability at short muscle lengths would be the lower energetic cost due to fewer cross-bridge interactions at short length compared with lengths that are closer to optimal overlap between actin and myosin filaments. However, two studies that explicitly investigated the idea of a length-dependent energy utilization in tibialis anterior muscle using 31 P-magnetic resonance spectroscopy ( 31 P-MRS) failed to show length-dependent energy consumption (2, 34).Recently, Place et al. (31) related the lower fatigability at short muscle lengths to a greater twitch potentiation at short compared with a longer length after a voluntary sustained contraction of the knee extensors at 20% maximal volun...

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