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Oxygen consumption, muscle activation intensity, and fascicle strain rate were measured over a range of speeds while animals ran unloaded vs. when they carried a trunk load equal to 22% of their body mass. Our results showed that loading produced no significant ( P &gt; 0.05) changes in kinematic patterns at any speed. In vivo muscle contractile strain patterns in the iliotibialis lateralis pars postacetabularis and the medial head of the gastrocnemius showed a significant increase in active stretch early in stance ( P &lt; 0.01), but muscle fascicle shortening velocity was not significantly affected by load carrying. The rate of oxygen consumption increased by 17% ( P &lt; 0.01) during loaded conditions, equivalent to 77% of the relative increase in mass. Additionally, relative increases in EMG intensity (quantified as mean spike amplitude) indicated less than proportional recruitment, consistent with force enhancement via stretch activation, in the proximal iliotibialis lateralis pars postacetabularis; however, a greater than proportional increase in the medial gastrocnemius was observed. As a result, when averaged for the two muscles, EMG intensity increased in direct proportion to the fractional increase in load carried.<\/jats:p>","DOI":"10.1152\/japplphysiol.01538.2005","type":"journal-article","created":{"date-parts":[[2006,6,30]],"date-time":"2006-06-30T14:52:16Z","timestamp":1151679136000},"page":"1060-1069","source":"Crossref","is-referenced-by-count":30,"title":["Effects of load carrying on metabolic cost and hindlimb muscle dynamics in guinea fowl (<i>Numida meleagris<\/i>)"],"prefix":"10.1152","volume":"101","author":[{"given":"C. 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