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Biomedical subjects

J J Knapik

Publications and source records attributed to J J Knapik.

At least 37 records · Page 2Linked to original sources
PubMed1999

Physiological factors in stretcher carriage performance.

In this study we examined the anthropometric and physiological factors that may account for the ability to carry a casualty on a stretcher. Eleven young soldiers were pretested to obtain their anthropometry, body composition, physical fitness, and muscle cross-sectional areas. They then performed a two-person manual carry of a stretcher containing an 82-kg manikin while walking on a treadmill at a speed of 4.8 km/h. Subjects walked until volitional fatigue, as indicated by slippage of the stretcher from their hands. Average (SD) carriage time was 2.7(1.4) min with a range of 1.4-6.4 min. A stepwise multiple linear regression revealed that forearm bone-plus-muscle cross-sectional area, thigh muscle cross-sectional area, and push-up performance accounted for most of the variance in hand carriage time (r2 = 0.99, P < 0.001). These data suggest that muscle cross-sectional area and upper-body muscular endurance are important physiological factors in the ability to carry a loaded stretcher by hand.

Adult↗
PubMed1999

Physical training and exercise-related injuries. Surveillance, research and injury prevention in military populations.

Athletes and soldiers must both develop and maintain high levels of physical fitness for the physically demanding tasks they perform; however, the routine physical activity necessary to achieve and sustain fitness can result in training-related injuries. This article reviews data from a systematic injury control programme developed by the US Army. Injury control requires 5 major steps: (i) surveillance to determine the size of the injury problem; (ii) studies to determine causes and risk factors for these injuries; (iii) studies to ascertain whether proposed interventions actually reduce injuries; (iv) implementation of effective interventions; and (v) monitoring to see whether interventions retain their effectiveness. Medical surveillance data from the US Army indicate that unintentional (accidental) injuries cause about 50% of deaths, 50% of disabilities, 30% of hospitalisations and 40 to 60% of outpatient visits. Epidemiological surveys show that the cumulative incidence of injuries (requiring an outpatient visit) in the 8 weeks of US Army basic training is about 25% for men and 55% for women; incidence rates for operational infantry, special forces and ranger units are about 10 to 12 injuries/100 soldier-months. Of the limited-duty days accrued by trainees and infantry soldiers who were treated in outpatient clinics, 80 to 90% were the result of training-related injuries. US Army studies document a number of potentially modifiable risk factors for these injuries, which include high amounts of running, low levels of physical fitness, high and low levels of flexibility, sedentary lifestyle and tobacco use, amongst others. Studies directed at interventions showed that limiting running distance can reduce the risk for stress fractures, that the use of ankle braces can reduce the likelihood of ankle sprains during airborne operations and that the use of shock-absorbing insoles does not reduce stress fractures during training. The US Army continues to develop a comprehensive injury prevention programme encompassing surveillance, research, programme implementation and monitoring. The findings from this programme, and the general principles of injury control therein, have a wide application in civilian sports and exercise programmes.

Accidents↗
PubMed1999

Risk factors for foot blisters during road marching: tobacco use, ethnicity, foot type, previous illness, and other factors.

Three hundred thirty-nine freshmen participating in cadet basic training at the U.S. Military Academy completed a questionnaire that asked them about their previous military experience, gender, ethnicity, injuries and illness experienced in the last 12 months, foot type, cigarette smoking habits, smokeless tobacco use, alcohol consumption, and sleep habits. They then performed a 21-km road march in about 6.5 hours. Their feet were examined for blisters before and after the march. Univariate analysis showed that risk factors for foot blisters included ethnicity (blacks at lower risk than others), a sickness in the last 12 months, no previous active duty military experience, use of smokeless tobacco, and flat feet (pes planus). Logistic regression indicated that all of these were independent blister risk factors with the exception of no previous active duty military experience.

Analysis of Variance↗
PubMed1999

Parachuting injuries during Operation Royal Dragon, Big Drop III, Fort Bragg, North Carolina, May 15/16, 1996.

On the night of May 15/16, 1996, the largest parachute assault of United States (US) and United Kingdom (UK) airborne forces in 52 years occurred at Fort Bragg, North Carolina. This paper describes the injuries sustained in that operation. A total of 4,754 (US, N = 3,066; UK, N = 1,688) aircraft exits were made, causing a total of 137 (US, N = 73; UK, N = 64) injuries in 117 personnel (US = 68; UK = 49). There were 15 hospital admissions (US = 8; UK = 7; p = 0.37) and no fatalities. The combined exit injury incidence was 24.6 injured soldiers per 1,000 exits. The US exit injury rate was 22 injured per 1,000 aircraft exits and the UK rate was 29 injured soldiers per 1,000 aircraft exits. This difference was not statistically significant (p = 0.25). Lower extremity sprains, strains, and fractures accounted for the majority of injuries in US and UK forces. UK soldiers sustained significantly more of these potentially incapacitating injuries than US troops, 16.1 per 1,000 exits versus 9.1 per 1,000 exits, respectively (chi 2 = 4.07; p = 0.043; relative risk [RR] = 1.70; 95% confidence interval [CI] = 1.01, 2.86). The UK forces sustained significantly more closed head injuries than US forces, 7.1 per 1,000 exits versus 2.3 per 1,000 exits, respectively (chi 2 = 6.4; p = 0.011; RR = 3.13; 95% CI = 1.23, 7.93). The UK forces also had significantly more soldiers with multiple injuries than US forces (RR = 9.15; 95% CI = 2.5, 39.7). Factors that may have influenced differences in injury incidence include differences in weight of personal equipment and possible differences between the drop zones.

Adolescent↗
PubMed1998

Influence of an antiperspirant on foot blister incidence during cross-country hiking.

BACKGROUND: Rubbing moist skin results in higher frictional forces than rubbing very dry skin. As friction increases, the probability of activity-related blisters also increases. Therefore reducing moisture may reduce blister incidence during physical activity. OBJECTIVE: We examined whether an antiperspirant can reduce foot blisters during hiking. METHODS: In a double-blind study, cadets attending the US Military Academy were separated into two groups that used either an antiperspirant (20% aluminum chloride hexahydrate in anhydrous ethyl alcohol) or placebo (anhydrous ethyl alcohol) preparation. Cadets were told to apply preparations to their feet for 5 consecutive nights. On day 6, cadets completed a 21-km hike, and their feet were examined for blisters before and after. RESULTS: Because of dropouts, the final sample size was 667 cadets with 328 in the antiperspirant group and 339 in the placebo group. There was a high rate of noncompliance with the treatment schedule: Cadets used the preparations from 0 to 5 nights before the hike. For cadets using the preparations at least 3 nights before the hike (n=269), the incidence of foot blisters was 21% for the antiperspirant group and 48% for the placebo group (P < 0.01). However, reports of skin irritation were 57% for the antiperspirant group and 6% for the placebo group (P < 0.01). CONCLUSION: A 20% solution of aluminum chloride hexahydrate in anhydrous ethyl alcohol may be effective in reducing foot blisters during hiking; however, the side effect of skin irritation should be considered and preventive measures studied to reduce this irritation.

Aluminum Chloride↗
PubMed1997

Soldier performance and strenuous road marching: influence of load mass and load distribution.

Fifteen male soldiers performed six maximal-effort, 20-km road marchers. They carried load masses of 34, 48, and 61 kg, using a standard military backpack with frame or an experimental doublepack. March times decreased as mass increased and were faster with the standard pack than with the double-pack. The doublepack resulted in less low back discomfort and a lower incidence of blisters at the highest load, but also resulted in more discomfort in the neck and hips. Neither load mass nor pack type affected soldiers' marksmanship ability, grenade throw accuracy, or cognitive ability. The maximal-effort march itself affected the marksmanship tasks by increasing the post-march vertical shot group dispersion. The concept of distributing the load mass more evenly around the center of mass of the body has both positive and negative aspects and warrants further investigation.

Blister↗
PubMed1996

Influence of age and physical training on measures of cardiorespiratory and muscle endurance.

This study describes associations between age, physical training and measures of muscle and cardiorespiratory endurance. The subjects were 5079 healthy male soldiers aged 18-53 years from 14 Army installations in the United States. The subjects completed as many push-ups as possible in 2 min, as many sit-ups as possible in 2 min, and performed a timed 3.2-km run. The training level was assessed by asking the subjects two questions about the frequency (times each week) and duration (hours each week) of their physical training. For all three performance events there were significant declines with age, but at a given age, groups that trained more demonstrated higher performance levels than groups that trained less. For the 3.2-km run, the age-associated rate of performance decline was less in the groups that trained more, and greater amounts of training resulted in progressively less performance decline with age. For push-ups and sit-ups, the training level did not systematically influence the age-related rate of performance decline. The results suggest that tasks involving different physiological systems may be influenced differentially by age and training. Training may slow age-associated performance declines in tasks requiring cardiorespiratory endurance but not in tasks requiring muscle endurance.

Adult↗
PubMed1996

Validity of an anthropometric estimate of thigh muscle cross-sectional area.

This study examined the validity of an anthropometric estimate of thigh muscle cross-sectional area using magnetic resonance imaging (MRI). The anthropometric model assumed that a cross section of the thigh could be represented as a circle with concentric circular layers of fat-plus-skin, muscle, and bone tissue. On 18 healthy, active men and women (mean +/- SD age = 23 +/- 5 yr), total thigh circumference (CT) was measured with a fiberglass tape, fat-plus-skin thickness was measured over the quadriceps (SQ) using calipers, and the distance across the medial and lateral femoral epicondyle (dE) was measured with calipers. Direct measurements of each tissue were obtained by planimetry of an MRI image taken at the same site as the circumference and skinfolds. Thigh muscle cross-sectional area (AM) was estimated as follows: [equation: see text] Mean +/- SD AM from MRI and anthropometry were 121.9 +/- 35.1 cm2 and 149.1 +/- 34.1 cm2 (r = 0.96, SEE = 10.1 cm2), respectively. Errors in the anthropometric approximations of AM were due to an overestimate of the total thigh cross-sectional area and an underestimate of fat-plus-skin compartment. Because of the close relationship between MRI and anthropometric estimates of AM, zero-intercept regression was used to produce the following final equation, applicable for use in populations studies of young, healthy, active men and women: [equation: see text]

Adult↗
PubMed1996

Influence of boot-sock systems on frequency and severity of foot blisters.

This study examined the infleunce of three types of boot-sock systems on incidence and severity of foot blisters. Participants were 357 men undergoing U.S. Marine recruit training at Parris Island, South Carolina. Each participant was assigned to one of three treatment groups. The first group wore the standard military boot sock consisting of a wool-cotton-nylon-Spandex combination. The second group wore the standard military boot sock with a thin inner or liner sock consisting of polyester. The third group wore a very thick, dense, prototype outer sock consisting of a wool-polypropylene combination over the same liner sock as the second group. Foot blister incidence was lower among participants who wore the the prototype boot sock and liner than among those wearing the standard military sock (40 vs. 69%, p < 0.001) or among subjects wearing the standard military sock with liner (40 vs. 77%, p < 0.001). Foot blisters and cellulitis severe enough to require medical attention occurred with greater frequency in the standard military sock group compared to both the prototype boot-sock group (24 vs. 11%, p = 0.02) and the standard military sock with liner group (24 vs. 9%, p < 0.01); there was no difference between the latter two groups. Blister reduction was most apparent in the early weeks of recruit training. The standard military sock with a polyester liner reduced the incidence of severe blisters, but the dense sock with the polyester liner reduced the overall incidence of blisters as well as the incidence of severe blisters.

Adult↗
PubMed1995

Friction blisters. Pathophysiology, prevention and treatment.

Blisters occur frequently, especially in vigorously active populations. Studies using respective rubbing techniques show that blisters result from frictional forces that mechanically separate epidermal cells at level of the stratum spinosum. Hydrostatic pressure causes the area of the separation to fill with a fluid that is similar in composition to plasma but has a lower protein level. About 6 hours after formation of the blister, cells in the blister base begin to take amino acids and nucleosides; at 24 hours, there is high mitotic activity in the basal cells; at 48 and 120 hours, new stratum granulosum and stratum corneum, respectively, can be seen. The magnitude of frictional forces (Ff) and the number of times that an object cycles across the skin determine the probability of blister development - the higher the Ff, the fewer the cycles necessary to produce a blister. Moist skin increases Ff, but very dry or very wet skin necessary to produce a blister. Moist skin increases Ff, but very dry or very wet skin decreases Ff. Blisters are more likely in skin areas that have a thick horny layer held tightly to underlying structures (e.g. palms of the hands or soles of the feet). More vigorous activity and the carrying of heavy loads during locomotion both appear to increase the likelihood of foot blisters. Antiperspirants with emollients and drying powders applied to the foot do not appear to decrease the probability of friction blisters. There is some evidence that foot blister incidence can be reduced by closed cell neoprene insoles. Wearing foot socks composed of acrylic results in fewer foot blisters in runners. A thin polyester sock, combined with a thick wool or polypropylene sock that maintains its bulk when exposed to sweat and compression reduces blister incidence in Marine recruits. Recent exposure of the skin to repeated low intensity Ff results in a number of adaptations including cellular proliferation and epidermal thickening, which may reduce the likelihood of blisters. More well-designed studies are necessary to determine which prevention strategies actually decrease blister probability. Clinical experience suggests draining intact blisters and maintaining the blister roof results in the least patient discomfort and may reduce the possibility of secondary infection. Treating deroofed blisters with hydrocolloid dressings provides pain relief and may allow patients to continue physical activity if necessary. There is no evidence that antibiotics influence blister healing. Clinical trials are needed to determine the efficacy of various blister treatment methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Blister↗
PubMed1995

Symptoms during load carrying: effects of mass and load distribution during a 20-km road march.

Soldiers must often carry heavy loads which can lead to symptoms of body soreness, aches, pains, and tiredness. This study assessed symptoms when soldiers carried loads in the standard U.S. Army ALICE pack (a single backpack) and in a prototype Double Pack (a two-pack system designed to alleviate symptoms by evenly distributing the load between a backpack and a frontpack). Each of 15 male soldiers completed a 20-km (12.4 mi) road march while carrying either 34, 48, or 61 kg (75, 105, or 135 lb) and while wearing either the ALICE pack or the Double Pack. Symptoms included feeling alert, good, and wide awake. Postmarch symptoms included tiredness, muscle tightness, and soreness of the legs, feet, back, and shoulders. Analyses of eight symptom factors showed that (a) as load increased, fatigue and muscle discomfort intensified, and alertness and feelings of well-being diminished and (b) distress and heat-illness indices were most intense at 61 kg with the Double Pack.

Adult↗
PubMed1994

Ambulatory foot contact monitor to estimate metabolic cost of human locomotion.

The rate of metabolic energy expenditure during locomotion (Mloco) is proportional to body weight (Wb) divided by the time during each stride that a single foot contacts the ground (tc) (Nature Lond. 346: 265-267, 1990). Using this knowledge, we developed an electronic foot contact monitor. Our objective was to derive and cross-validate an equation for estimation Mloco from Wb/tc. Twelve males were tested [age = 19.4 +/- 1.4 (SD) yr, Wb = 78.4 +/- 8.0 kg] during horizontal treadmill walking (0.89, 1.34, and 1.79 m/s) and running (2.46, 2.91, and 3.35 m/s). Measured Mloco was defined as the total rate of energy expenditure, measured by indirect calorimetry, minus the estimated rate of resting energy expenditure. The equation to estimate Mloco was derived in six randomly selected subjects: Mloco = 3.702.(Wb/tc) - 149.6 (r2 = 0.93). Cross-validation in the remaining six subjects showed that estimated and measured Mloco were highly correlated (r2 = 0.97). The average individual error between estimated and measured Mloco was 0% (range -22 to 29%). In conclusion, Mloco can be accurately estimated from Wb and measurements of tc made by an ambulatory foot contact monitor.

Adult↗
PubMed1994

Exercise, training and injuries.

Although exercise results in a number of well documented physical fitness and health benefits, accruing such benefits entails a risk of exercise-related injuries. Musculoskeletal injuries occur frequently among fitness programme participants, runners, athletes, military recruits and others who engage in routine vigorous exercise. The same parameters of exercise (intensity, duration and frequency) that determine the positive fitness and health effects of physical training also appear to influence the risk of injuries. Studies of runners and other physically active groups have consistently demonstrated that greater duration and frequency of exercise are associated with higher risks of injury. However, the sports medicine literature shows little association between exercise intensity and injuries, a finding which may be misleading. The strongest and most consistent association reported exists between greater total amounts of exercise and higher risks of injury. This is not surprising, since the total amount of exercise is the product of the intensity, duration and frequency of exercise. Recent military research confirms the finding that higher volumes of running are associated with higher rates of injury. Furthermore, the study of army recruits suggests that greater amounts of exercise not only result in greater risks of injury, but in some instances may also impart no additional increase in fitness, a finding consistent with an earlier study of civilian runners. Several military studies also demonstrate that those recruits who have been more physically active in the past are less likely to be injured during basic training. These military studies also document a number of other factors, such as older age, smoking, sedentary jobs and lifestyle, high or low flexibility and high arches of the feet, which may contribute to or modify the risks for exercise-related injuries. In conclusion, the present review suggest that, for activities such as running, specific parameters of exercise may contribute to the overall risk of injuries in rough proportion to their contribution to the total amount of activity performed. Also, better knowledge of the effects of the parameters of training and other factors on the risks of exercise-related injuries is necessary to make more judicious choices about how to best achieve the benefits of exercise and to prevent injuries.

Athletic Injuries↗
PubMed1994

Physical fitness and cardiovascular disease risk factors in senior military officers.

Over a 5-year period (1986-1990), 1,223 male, senior military officers were tested to determine lipoprotein profiles, body composition (by densitometry), peak oxygen consumption (VO2 peak by graded, treadmill walking), and strength (one repetition maximum). Average (+/- SD) VO2 peak and body fat were 44.9 +/- 6.7 ml/kg x min and 24.4 +/- 5.1%, respectively. Although the average VO2 peak of these individuals is in the top 10-15% of this age group, nearly 39% are over-fat (by U.S. Army Regulation 600-9). Mean (+/- SD) total cholesterol, high-density lipoproteins, low-density lipoproteins, and triglycerides were 205 +/- 36, 50 +/- 12, 134 +/- 32, and 108 +/- 71 mg%, respectively. These results reflect an apparently healthy diet and lifestyle, which was strengthened, for the most part, when an average Framingham risk index (FRI) of approximately 2.3 was calculated. The low mean FRI for this group may possibly be attributed to lower total cholesterol and smoking rates than the average 45-year-old man in the Framingham study. The results of the testing indicate that this group generally has a high aerobic capacity, is normotensive, non-obese, and at low risk for the development of cardiovascular disease.

Adult↗
PubMed1988

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes.

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.

Adult↗
PubMed1988

Influence of fasting on carbohydrate and fat metabolism during rest and exercise in men.

Metabolic effects of an overnight fast (postabsorptive state, PA) or a 3.5-day fast (fasted state, F) were compared in eight healthy young men at rest and during exercise to exhaustion at 45% maximum O2 uptake. Glucose rate of appearance (Ra) and disappearance (Rd) were calculated from plasma glucose enrichment during a primed, continuous infusion of [6,6-2H]glucose. Serum substrates and insulin levels were measured and glycogen content of the vastus lateralis was determined in biopsies taken before and after exercise. At rest, whole-body glucose flux (determined by the deuterated tracer) and carbohydrate oxidation (determined from respiratory exchange ratio) were lower in F than PA, but muscle glycogen levels were similar. During exercise, glucose flux, whole-body carbohydrate oxidation, and the rate of muscle glycogen utilization were significantly lower during the fast. In the PA state, glucose Ra and Rd increased together throughout exercise. However, in the F state Ra exceeded Rd during the 1st h of exercise, causing an increase in plasma glucose to levels similar to those of the PA state. The increase in glucose flux was markedly less throughout F exercise. Lower carbohydrate utilization in the F state was accompanied by higher circulating fatty acids and ketone bodies, lower plasma insulin levels, and the maintenance of physical performance reflected by similar time to exhaustion.

Adult↗
PubMed1987

Influence of a 3.5 day fast on physical performance.

Eight young men were tested for strength, anaerobic capacity and aerobic endurance in a post absorptive state and after a 3.5 day fast. Strength was tested both isokinetically (elbow flexors, 0.52 rad x s-1 and 3.14 rad x s-1) and isometrically. Anaerobic capacity was evaluated by having subjects perform 50 rapidly repeated isokinetic contractions of the elbow flexors at 3.14 rad x s-1. Aerobic endurance was measured as time to volitional fatigue during a cycle ergometer exercise at 45% VO2max. Measures of VO2, VE, heart rate, and ratings of perceived exertion were obtained prior to and during the cycle exercise. The 3.5 day fast did not influence isometric strength, anaerobic capacity or aerobic endurance. Isokinetic strength was significantly reduced (approximately 10%) at both velocities. VO2, VE and perceived exertion were not affected by fasting. Fasting significantly increased heart rate during exercise but not at rest. It was concluded that there are minimal impairments in physical performance parameters measured here as a result of a 3.5 day fast.

Adult↗