Stick balancing at the fingertip is a powerful paradigm for the study of the control of human balance. Here we show that the mean stick balancing time is increased by about two-fold when a subject stands on a vibrating platform that produces vertical vibrations at the fingertip (0.001 m, 15–50 Hz). High speed motion capture measurements in three dimensions demonstrate that vibration does not shorten the neural latency for stick balancing or change the distribution of the changes in speed made by the fingertip during stick balancing, but does decrease the amplitude of the fluctuations in the relative positions of the fingertip and the tip of the stick in the horizontal plane, A(x,y). The findings are interpreted in terms of a time-delayed “drift and act” control mechanism in which controlling movements are made only when controlled variables exceed a threshold, i.e. the stick survival time measures the time to cross a threshold. The amplitude of the oscillations produced by this mechanism can be decreased by parametric excitation. It is shown that a plot of the logarithm of the vibration-induced increase in stick balancing skill, a measure of the mean first passage time, versus the standard deviation of the A(x,y) fluctuations, a measure of the distance to the threshold, is linear as expected for the times to cross a threshold in a stochastic dynamical system. These observations suggest that the balanced state represents a complex time–dependent state which is situated in a basin of attraction that is of the same order of size. The fact that vibration amplitude can benefit balance control raises the possibility of minimizing risk of falling through appropriate changes in the design of footwear and roughness of the walking surfaces.

The purpose of this study was to examine blood pressure (BP), heart rate (HR), and cardiac vagal reactivation (VR) after an aerobic training session (ATS), a strength training session (STS), and a combined aerobic and strength training session (ASTS) in normotensive men. Eleven healthy men (age 26.8 ± 2.9 years, body mass index 24.3 ± 1.6 kg·m) with at least 6 months of strength and aerobic training experience performed an STS, an ATS, and an ASTS in a counterbalanced crossover design. Blood pressure and HR were measured at rest and at 15-minute intervals post-training for 1 hour. Vagal reactivation was measured during the first minute immediately post-exercise. After STS and ASTS, systolic BP (SBP) and mean arterial BP (MAP) remained significantly lower than at rest at all time intervals (p < 0.05). After ATS, SBP was significantly lower than at rest at 30 minutes and beyond (p < 0.01); however, no significant differences were observed for MAP. Post-training HR remained high after STS and ASTS at all intervals (p < 0.01). However, after ATS, the HR remained high only at the 15-minute post-exercise interval (p < 0.01). Vagal reactivation was significantly less pronounced after the first 30 seconds post-exercise (p < 0.01) in ASTS (531.3 ± 329.6 seconds) than in ATS (220.7 ± 88.5 seconds) and in STS (317.6 ± 158.5 seconds). The delta of the HR decrease at 60 seconds post-exercise was greater (p < 0.00) in ATS (33.4 ± 12.7 b·min) than in STS (14.1 ± 7.2 b·min) and in ASTS (11.4 ± 7.1 b·min). In conclusion, post-exercise BP reduction was independent of the type of exercise; however, HR remained significantly greater after combination of strength and aerobic exercise, implying a reduction in cardiac VR after this type of training. Therefore, strength and conditioning professionals may prescribe aerobic, strength, or a combination of aerobic and strength exercise to assist individuals concerned with BP control, thus allowing for variety in training while similarly impacting post-exercise SBP regardless of desired exercise modality.

The purpose of this study was to develop a submaximal, 1.5-mile endurance test for college-aged students using walking, jogging, or running exercise. College students (N = 101: 52 men, 47 women), ages 18-26years, successfully completed the 1.5-mile test twice, and a maximal graded exercise test. Participants were instructed to achieve a "somewhat hard" exercise intensity (rating of perceived exertion = 13) and maintain a steady pace throughout each 1.5-mile test. Multiple linear regression generated the following prediction equation: VO2 max = 65.404 + 7.707 x gender (1 = male; 0 =female) - 0.159 x body mass (kg) - 0.843 x elapsed exercise time (min; walking, jogging orrunning). This equation shows acceptable validity (R = .86, SEE = 3.37 ml x kg(-1) min(-1)) similar to the accuracy of comparable field tests, and reliability (ICC = .93) is also comparable to similar models. The statistical shrinkage is minimal (R(press) = 0.85, SEE(press) = 3.51 ml x kg(-) x min(-1)); hence, it should provide comparable results when applied to other similar samples. A regression model (R =.90, and SEE = 2.87 ml x kg(-1) min(-1)) including exercise heart rate was also developed: VO2 max = 100.162 +/- 7.301 x gender(1 = male; 0 =female) - 0.164 x body mass (kg) - 1.273 x elapsed exercise time -0.156 x exercise heart rate, for those who have access to electronic heart rate monitors. This submaximal 1.5-mile test accurately predicts maximal oxygen uptake (VO2max) without measuring heart rate and is similar to the 1.5-mile run in that it allowsfor mass testing and requires only a flat, measured distance and a stopwatch. Further, it can accommodate a wide range of fitness levels (from walkers to runners).

Stress fractures are a common overuse problem among military trainees resulting in preventable morbidity, prolonged training, and long-term disability following military service. Femoral neck stress fractures (FNSFs) account for 2% of all stress fractures but result in disproportionate burden in terms of cost and convalescence. The purpose of this study was to describe and investigate FNSF in U.S. Air Force basic trainees and to present new data on risks factors for developing FNSF. We examined 47 cases of FNSF occurring in Air Force basic trainees between 2008 and 2011 and 94 controls using a matched case-control model. Analysis with t tests and conditional logistic regression found the risk of FNSF was not associated with body mass index or abdominal circumference. Female gender (p < 0.001) and slower run time significantly increased risk of FNSF (1.49 OR, p < 0.001; 95% CI 1.19-1.86). A greater number of push-up and sit-up repetitions significantly reduced risk of FNSF (0.55 OR, p = 0.03; 95% CI 0.32-0.93; 0.62 OR, p = 0.04; 95% CI 0.4-0.98) for females. In this study body mass index was not correlated with FNSF risk; however, physical fitness level on arrival to training and female gender were significantly associated with risk of FNSF.

Only the Arm Curl and Chair Stand tests were valid surrogates. Although multiple field tests to measure strength in a clinical setting may be desirable, these data support limiting functional testing to the Arm Curl for upper-body and the Chair Stand for lower-body strength assessment.