http://hdl.handle.net/2173/564 Fri, 24 May 2013 22:59:53 GMT 2013-05-24T22:59:53Z http://hdl.handle.net/2173/110622 Title: A comparison of the moment arms of pelvic limb muscles in horses bred for acceleration (Quarter Horse) and endurance (Arab). Authors: Crook, Tracy; Cruickshank, S. E.; McGowan, C. M.; Stubbs, N.; Wilson, Alan M.; Hodson-Tole, Emma F.; Payne, R. C. Abstract: Selective breeding for performance has resulted in distinct breeds of horse, such as the Quarter Horse (bred for acceleration) and the Arab (bred for endurance). Rapid acceleration, seen during Quarter Horse racing, requires fast powerful muscular contraction and the generation of large joint torques, particularly by the hind limb muscles. This study compared hind limb moment arm lengths in the Quarter Horse and Arab. We hypothesized that Quarter Horse hind limb extensor muscles would have longer moment arms when compared to the Arab, conferring a greater potential for torque generation at the hip, stifle and tarsus during limb extension. Six Quarter Horse and six Arab hind limbs were dissected to determine muscle moment arm lengths for the following muscles: gluteus medius, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius (medialis and lateralis) and tibialis cranialis. The moment arms of biceps femoris (acting at the hip) and gastrocnemius lateralis (acting at the stifle) were significantly longer in the Quarter Horse, although the length of the remaining muscle moment arms were similar in both breeds of horse. All the Quarter Horse muscles were capable of generating greater muscle moments owing to their greater physiological cross-sectional area (PCSA) and therefore greater isometric force potential, which suggests that PCSA is a better determinant of muscle torque than moment arm length in these two breeds of horse. With the exception of gastrocnemius and tibialis cranialis, the observed muscle fascicle length to moment arm ratio (MFL : MA ratio) was greater for the Arab horse muscles. It appears that the Arab muscles have the potential to operate at slower velocities of contraction and hence generate greater force outputs when compared to the Quarter Horse muscles working over a similar range of joint motion; this would indicate that Arab hind limb muscles are optimized to function at maximum economy rather than maximum power output. Description: Full-text of this article is not available in this e-prints service. This article was originally published following peer-review in Journal of Anatomy, published by and copyright Wiley-Blackwell Publishing Ltd.. Thu, 01 Jul 2010 00:00:00 GMT http://hdl.handle.net/2173/110622 2010-07-01T00:00:00Z http://hdl.handle.net/2173/109561 Title: Muscle tissue oxygenation and VEGF in VO2-matched vibration and squatting exercise Authors: Rittweger, Jörn; Moss, Andrew D.; Colier, Willy; Stewart, Claire E.; Degens, Hans Abstract: Exposure to vibration has traditionally been associated with compromised perfusion. This study investigated whether blood supply during whole body vibration (WBV), as an exercise modality, is in proportion to the metabolic demand by the contracting musculature. As a secondary aim, serum levels of vascular endothelial growth factor (VEGF) were assessed. Ten young healthy males performed WBV and dynamic shallow squatting (Squat) exercise at comparable levels of oxygen uptake for 3 min. Changes in oxygenated, deoxygenated and total haemoglobin (O2Hb, HHb and tHb, respectively) along with tissue oxygenation index (TOI) were measured continuously before, during and after the exercise by near-infrared spectroscopy (NIRS, Portamon, Artinis Medical Systems, Zetten, The Netherlands). Vascular endothelial growth factor-A blood levels before and after exercise were assessed by ELISA. Oxygen uptake was comparable in Squat and WBV (11·4 and 10·7 ml kg−1 min−1), respectively, P = 0·49), as were all other cardiopulmonary variables. Near-infrared spectroscopy data were found to be non-stationary during and shortly after WBV, but stationary in Squat. There was an increase in O2Hb and TOI, and a decrease in HHb during the first 30 s of WBV, but no significant change was observed during Squat. No group difference was found in VEGF serum levels. These results suggest that oxygen supply during WBV is sufficient, and oxygenation is even enhanced during the first approximately 30 s. Most likely, the transient response is because of local vascular regulatory mechanisms and due to muscle contraction mechanics. This might become clinically relevant under pathological conditions, e.g. in vascular disorders. Description: Full-text of this article is not available in this e-prints service. This article was originally published following peer-review in Clinical Physiology and Functional Imaging, published by and copyright Wiley-Blackwell Publishing Ltd.. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2173/109561 2010-01-01T00:00:00Z http://hdl.handle.net/2173/109485 Title: Locomotor changes in length and EMG activity of feline medial gastrocnemius muscle following paralysis of two synergists. Authors: Maas, Huub; Gregor, Robert J.; Hodson-Tole, Emma F.; Farrell, Brad J.; English, Arthur W.; Prilutsky, Boris I. Abstract: The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle extensor during walking shortly after paralysis of its synergists is not fully understood. It is possible that due to greater ankle flexion in stance in this situation, muscle spindles are stretched to a greater extent and, thus, contribute to the EMG enhancement. However, also changes in force feedback and central drive may play a role. The aim of the present study was to investigate the short-term (1- to 2-week post-op) effects of lateral gastrocnemius (LG) and soleus (SO) denervation on muscle fascicle and muscle-tendon unit (MTU) length changes, as well as EMG activity of the intact medial gastrocnemius (MG) muscle in stance during overground walking on level (0%), downslope (-50%, presumably enhancing stretch of ankle extensors in stance) and upslope (+50%, enhancing load on ankle extensors) surfaces. Fascicle length was measured directly using sonomicrometry, and MTU length was calculated from joint kinematics. For each slope condition, LG-SO denervation resulted in an increase in MTU stretch and peak stretch velocity of the intact MG in early stance. MG muscle fascicle stretch and peak stretch velocity were also higher than before denervation in downslope walking. Denervation significantly decreased the magnitude of MG fascicle shortening and peak shortening velocity during early stance in level and upslope walking. MG EMG magnitude in the swing and stance phases was substantially greater after denervation, with a relatively greater increase during stance of level and upslope walking. These results suggest that the fascicle length patterns of MG muscle are significantly altered when two of its synergists are in a state of paralysis. Further, the compensatory increase in MG EMG is likely mediated by enhanced MG length feedback during downslope walking, enhanced feedback from load-sensitive receptors during upslope walking and enhanced central drive in all walking conditions. Description: The original publication is available at www.springerlink.com Tue, 01 Jun 2010 00:00:00 GMT http://hdl.handle.net/2173/109485 2010-06-01T00:00:00Z http://hdl.handle.net/2173/109466 Title: Preservation of eccentric strength in older adults: evidence, mechanisms and implications for training and rehabilitation. Authors: Roig, Marc; Macintyre, Donna L.; Eng, Janice J; Narici, Marco V.; Maganaris, Constantinos N.; Reid, W. Darlene Abstract: Overall reductions in muscle strength typically accompany the aging process. However, older adults show a relatively preserved capacity of producing eccentric strength. The preservation of eccentric strength in older adults is a well-established phenomenon, occurring indiscriminately across different muscle groups, independent of age-related architectural changes in muscle structure and velocity of movement. The mechanisms for the preservation of eccentric strength appear to be mechanical and cellular in origin and include both passive and active elements regulating muscle stiffness. The age-related accumulation of non-contractile material in the muscle-tendon unit increases passive stiffness, which might offer mechanical advantage during eccentric contractions. In addition, the preserved muscle tension and increased instantaneous stiffness of old muscle fibers during stretch increase active stiffness, which might enhance eccentric strength. The fact that the preservation of eccentric strength is present in people with chronic conditions when compared to age-matched healthy controls indicates that the aging process per se does not exclusively mediate the preservation of eccentric strength. Physical inactivity, which is common in elderly and people with chronic conditions, is a potential factor regulating the preservation of eccentric strength. When compared to concentric strength, the magnitude of preservation of eccentric strength in older adults ranges from 2% to 48% with a mean value of 21.6% from all studies. This functional reserve of eccentric strength might be clinically relevant, especially to initiate resistance training and rehabilitation programs in individuals with low levels of strength. Description: Full-text of this article is not available in this e-prints service. This article was originally published following peer-review in Experimental Gerontology, published by and copyright Elsevier. Tue, 01 Jun 2010 00:00:00 GMT http://hdl.handle.net/2173/109466 2010-06-01T00:00:00Z