A sensitive, reliable, field-expedient test may be valuable for monitoring interventions during periods of anticipated physical performance decline. The purpose of this study was to determine the capabilities of unloaded jumping tests for detecting decrements in physical performance following eight days of military sustained operations. Twenty-nine U. S. Marines (24 +/- 1 y; 180 +/- 6 cm; 82.5 +/- 8.2 kg) performed 1, 5 and 30 repetition(s) of unloaded countermovement jumps (UJ) before and after eight days of sustained operations (SUSOPS). Jump performance data was collected simultaneously using a switch mat (SM) and a linear position transducer (LPT). Jump height (m) and power (W) were highest using 1 UJ and declined 4.9 and 8.9%, respectively after SUSOPS. Jump power (JP) declined progressively over 30 UJ (20%). Five UJ offered no advantages over 1 UJ and was inadequate to examine changes in muscle fatigability (pre: 1294 +/- 138 W; post: 1250 +/- 165 W). The SM and a LPT were in agreement and had a high correlation (r = 0.92). One UJ was a sensitive, easy to implement test for monitoring the collective impact of high physical, nutritional, cognitive, and environmental stress on an individuals' physical performance before and after 8 days of SUSOPS, suggesting decrements in physical performance associated with overreaching can be detected by simply administered field-expedient jumping tests.

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The pulsatile release of growth hormone (GH) and luteinizing hormone (LH) from the anterior pituitary gland is integral for signaling secretion of insulin-like growth factor (IGF)-I and testosterone, respectively. This study examined the hypothesis that 84 h of sustained physical exertion with caloric and sleep restriction alters the secretion of GH and LH. Ten male soldiers [22 yr (SD 3), 183 cm (SD 7), 87 kg (SD 8)] had blood drawn overnight from 1800 to 0600 every 20 min for GH, LH, and leptin and every 2 h for IGF-I (total and free), IGF binding proteins-1 and -3, testosterone (total and free), glucose, and free fatty acids during a control week and after 84 h of military operational stress. Time-series cluster and deconvolution analyses assessed the secretion parameters of GH and LH. Significant results (P < or = 0.05) were as follows: body mass (-3%), fat-free mass (-2.3%), and fat mass (-7.3%) declined after military operational stress. GH and LH secretion burst amplitude (approximately 50%) and overnight pulsatile secretion (approximately 50%), IGF binding protein-1 (+67%), and free fatty acids (+33%) increased, whereas leptin (-47%), total (-27%) and free IGF-I (-32%), total (-24%) and free testosterone (-30%), and IGF binding protein-3 (-6%) decreased. GH and LH pulse number were unaffected. Because GH and LH positively regulate IGF-I and testosterone, these data imply that the physiological strain induced a certain degree of peripheral resistance. During periods of energy deficiency, amplitude modulation of GH and LH pulses may precede alterations in pulse numbers.

Participation in resistance training increased total IGF-I and reduced IGFBP-1 concentrations during acute RE, indicating exercise mode-specific adaptations in the circulating IGF-I system.