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Santtila, M, Kyröläinen, H, and Häkkinen, K. Changes in maximal and explosive strength, electromyography, and muscle thickness of lower and upper extremities induced by combined strength and endurance training in soldiers. J Strength Cond Res 23(4): 1300-1308, 2009-The purpose of present study was to examine to what extent an 8-week endurance-based military training period interferes with muscle strength development in the conscripts (n = 72) compared with that caused by sport-related military training with added strength training (ST) or endurance training (ET). More specifically, we examined the effects of these 3 training modes on maximal isometric force, maximal rate of force development (RFD), electromyography (EMG), and muscle thickness of the lower and upper extremities. The measurements included isometric force-time parameters of leg and arm extensors and EMG activity from the vastus lateralis, vastus medialis, rectus femoris, and triceps brachii muscles. The 8-week basic training period combined with added ST and ET significantly improved maximal bilateral isometric force of the arm extensors in ST by 11.8% (p < 0.001), ET by 13.9% (p < 0.001), and normal training (NT) by 7.8% (p < 0.05). Strength training and ET showed significant increases in maximal EMG activity of the trained arm muscles. A significant increase was observed in maximal RFD of the upper extremities only in ST by 28.1% (p < 0.05). Both ST and ET increased their maximal leg extension strength by 12.9% (p < 0.01) and 9.1% (p < 0.05), respectively, whereas no significant change occurred in NT (5.2%, p = 0.45). No significant changes were observed in the shape of the force-time curves of leg extensors. No increases occurred in muscle thickness either in the lower or upper extremities. The present BT training with a large amount of endurance-based military training interfered with strength development, and especially, explosive power development of the lower extremities in the ST group. The optimal improvements in neuromuscular characteristics may not be possible without some decreases in the amount of the endurance-based military training and/or some increases in the amount of the maximal/explosive strength training during the BT.