Performance requirements of physically strenuous occupations: validating minimum standards for muscular strength and endurance.

Employment rights legislative mandates passed in the USA over the last three decades emphasize the importance of validating performance standards for physically strenuous occupations. This study validated minimally acceptable standards for the muscular strength and endurance necessary to perform fire suppression activities. Incumbent firefighters (n=153) selected for key demographic characteristics completed a simulated set of firefighting tasks (Fire Suppression Evolution) and then a Predictor Test Battery of physical abilities tests. Regression analysis revealed that three predictor test items (hose drag/high rise pack carry; arm lift; arm endurance) combined to significantly predict performance time of the Fire Suppression Evolution (p < or =0.01). Firefighters (n=41) rating videotaped performance times of the Fire Suppression Evolution determined that more than one-half a standard deviation slower than the mean time established by the incumbents reflected unacceptable performance. Approximately 80% of incumbent firefighters passed the minimally acceptable performance standard. Use of the 3-predictor test battery would correctly identify 89% of successful performers and 72% of unsuccessful performers. This study demonstrates that validation of minimal physical performance standards will identify a cohort of individuals with a high probability of not being able to perform critical fire suppression activities. This finding has important implications for examining the relationship between physical performance standards and medical and economic outcomes.

Brain norepinephrine changes with simulated weightlessness and relation to exercise training.

Maintenance of nervous system function during periods of a deconditioning syndrome is important to prevent diminished psychological/behavioral, and physiological function observed during periods of bed rest, physical inactivity, and weightlessness. A main neurotransmitter is norepinephrine (NE), and its regulation yields insight into nervous system function. This research tested the hypotheses that, 1) deconditioning syndrome induced by simulated weightlessness of 9 days via the head-down tilt (HDT) model results in a blunted noradrenergic turnover rate in selected brain tissue and, 2) that exercise training acts as a countermeasure for these changes in noradrenergic activity. Male Sprague-Dawley rats (3 months, n = 60) were divided into either a HDT (HDT, n = 20), cage control (CAGE-CN, n = 20) or an exercise trained HDT (HDT-EX, n = 20) group. Each group was further subdivided into a saline (n = 10) or alpha-methyl-tyrosine (AM, n = 10) (200 mg/kg) injected subgroup. Animals in the HDT groups were tail suspended in a 30 degrees head-down tilt position for 9 days. Norepinephrine turnover was determined 3 h following administration of saline or alpha-methyl-para-tyrosine. The NE turnover rate (ng gm(-1) x h(-1)) for the CN, HDT, and HDT-EX groups, respectively, were as follows: locus coeruleus, 63 +/- 33, *134 +/- 65, 85 +/- 61; hypothalamus, 195 +/- 50, *47 +/- 47; *93 +/- 34; cerebellum, 10 +/- 18, *65 +/- 15, *53 +/- 19; cerebral cortex, 6 +/- 20, *28 +/- 15, *68 +/- 22. (*Denotes significant difference from the control group at the p < or = 0.05 level of significance; +denotes significant difference from the HDT group at the p < or = 0.05 level of significance.) These findings suggest that: 1) norepinephrine turnover rate adapts in a tissue-specific manner following a 9-day tail suspension, 2) increased norepinephrine turnover rates and norepinephrine tissue content in the HDT group are consistent with neural adaptation to a chronic stress response.

Young and old subjects matched for aerobic capacity have similar noradrenergic responses to exercise.

Sympathetic nervous system activity as indicated by circulating norepinephrine has been demonstrated to increase with advancing chronological age both at rest and during submaximal exercise. Much of the earlier work investigating this aging phenomenon used a younger group that had a higher peak oxygen consumption (VO2) than did the older group, which made comparisons difficult. In the present study, young [n = 7, 36 +/- 1.0 (SE) yr] and old subjects (n = 8, 61 +/- 1.2 yr) were matched on peak VO2 and then exercised at approximately the same relative submaximal VO2 (75%) and power output on a cycle ergometer for 21 min. Blood samples were collected at rest and in the 7th, 14th, and last minute of a 21-min exercise bout via an indwelling catheter in an antecubital vein. The norepinephrine responses for the young and old groups, respectively, were as follows: rest, 486 +/- 111 vs. 673 +/- 108; 7 min, 1,258 +/- 255 vs. 1,185 +/- 172; 14 min, 1,639 +/- 316 vs. 1,528 +/- 288; and 21 min, 2,038 +/- 488 vs. 1,936 +/- 453 pg/ml. These responses were not significantly different between the groups at any time period. The epinephrine values for the age groups were not statistically different: rest, 115 +/- 60 vs 88 +/- 51; 7 min, 140 +/- 18 vs. 326 +/- 88; 14 min, 216 +/- 33 vs. 366 +/- 104; and 21 min, 324 +/- 100 vs. 447 +/- 113 pg/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle morphological and biochemical adaptations to training in obese Zucker rats.

The purposes of the present study were to characterize the histochemical and enzymatic profiles of various hindlimb skeletal muscles, as well as to determine maximal O2 consumption (VO2max) and respiratory exchange ratios (R) during steady-state exercise in the obese Zucker rat. The changes that occurred in these parameters in response to a 6-wk training program were then assessed. Obese rats were randomly assigned to a sedentary or training group. Lean littermates served as a second control. Training consisted of treadmill running at 18 m/min up an 8% grade, 1.5 h/day, 5 day/wk for 6 wk. During week 6, VO2max and R during a steady-state run (74% max) were determined. After 2 days of inactivity, hindlimb muscles were excised, stained for fiber type and capillaries, and assayed for hexokinase, citrate synthase, cytochrome oxidase, and beta-hydroxyacetyl-CoA dehydrogenase. The obese sedentary rats demonstrated greater oxidative enzyme activities per gram of muscle tissue than their lean littermates, greater R values during submaximal exercise of the same relative intensity, and greater absolute VO2max values. Training resulted in a 20-56% increase in oxidative enzymes, a 10% increase in VO2max, and an increase in capillary density in the soleus and plantaris. There was no alteration in R values during exercise at 74% VO2max or in fiber type composition in response to exercise training. Results suggest that the muscle of the obese Zucker rat manifests a greater oxidative capacity than the muscle of its lean littermates. The apparent inability of the obese rat to increase its use of fat during submaximal exercise of the same relative intensity in response to training remains to be elucidated.

Skeletal muscle glucose transport in obese Zucker rats after exercise training.

Exercise training has been found to reduce the muscle insulin resistance of the obese Zucker rat (fa/fa). The purpose of the present study was to determine whether this reduction in muscle insulin resistance was associated with an improvement in the glucose transport process and if it was fiber-type specific. Rats were randomly assigned to a sedentary or training group. Training consisted of treadmill running at 18 m/min up an 8% grade, 1.5 h/day, 5 days/wk, for 6-8 wk. The rate of muscle glucose transport was assessed in the absence of insulin and in the presence of a physiological (0.15 mU/ml), a submaximal (1.50 mU/ml), and a maximal (15.0 mU/ml) insulin concentration by determining the rate of 3-O-methyl-D-glucose (3-OMG) accumulation during hindlimb perfusion. The average 3-OMG transport rate of the red gastrocnemii (fast-twitch oxidative-glycolytic fibers) was significantly higher in the trained compared with the sedentary obese rats in the absence of insulin and in the presence of the three insulin concentrations. Significant improvements in 3-OMG transport were also observed in the plantarii (mixed fibers) of trained obese rats in the presence of 0, 0.15, and 15.0 mU/ml insulin. Training appeared to have little effect on the insulin-stimulated 3-OMG transport of the soleus (slow-twitch oxidative fibers) or white gastrocnemius (fast-twitch glycolytic fibers). The results suggest that the improvement in the muscle insulin resistance of the obese Zucker rat after moderate endurance training was associated with an improvement in the glucose transport process but that it was fiber-type specific.