David R. Pendergast

A Preliminary Study of Subsymptom Threshold Exercise Training for Refractory Post-concussion Syndrome

Objective:To evaluate the safety and effectiveness of subsymptom threshold exercise training for the treatment of post-concussion syndrome (PCS). Design:Prospective case series. Setting:University Sports Medicine Concussion Clinic. Participants:Twelve refractory patients with PCS (6 athletes and 6 nonathletes). Intervention:Treadmill test to symptom exacerbation threshold (ST) before and after 2 to 3 weeks of baseline. Subjects then exercised 5 to 6 days per week at 80% ST heart rate (HR) until voluntary peak exertion without symptom exacerbation. Treadmill testing was repeated every 3 weeks. Main Outcome Measures:Adverse reactions to exercise, PCS symptoms, HR, systolic blood pressure (SBP), achievement of maximal exertion, and return to work/sport. Results:Pretreatment, ST occurred at low exercise HR (147 ± 27 bpm) and SBP (142 ± 6 mm Hg). After treatment, subjects exercised longer (9.75 ± 6.38 minutes to 18.67 ± 2.53 minutes, P = .001) and achieved peak HR (179 ± 17 bpm) and SBP (156 ± 13 mm Hg), both P < .001 versus pretreatment, without symptom exacerbation. Time series analysis showed significant change in rate of symptom reduction for all subjects and reduced mean symptom number in 8/11. Rate of PCS symptom improvement was related to peak exercise HR (r = −0.55, P = .04). Athletes recovered faster than nonathletes (25 ± 8.7 vs 74.8 ± 27.2 days, P = .01). No adverse events were reported. Athletes returned to sport and nonathletes to work. Conclusions:Treatment with controlled exercise is a safe program that appears to improve PCS symptoms when compared with a no-treatment baseline. A randomized controlled study is warranted.

Quantitative effects of physical therapy on muscular and functional performance in subjects with osteoarthritis of the knees

Osteoarthritis (OA) of the knees is a functionally limiting disability. Physical therapy (PT) is considered a useful treatment for OA, although evidence is qualitative. The purpose of this study was to quantitatively measure the effects of a 3-month PT program (n = 40; 20 men and 20 women) with knee OA. Muscle function and functional assessment parameters were measured. All data were analyzed by repeated measures analysis of variance (p < 0.05). There were no significant changes in handgrip strength and endurance, limb volume, or angular velocity after PT. Maximal muscle length was significantly increased. Muscle strength significantly increased for the hamstrings (9% and 19%) and quadriceps (8% and 24%) for the men and women, respectively. Endurance improved for the quadriceps (26% and 39%) and hamstrings (18% and 28%) for men and women, respectively. Functionally, there were significant improvements in the ability to climb stairs, rise from a chair, and walk. Walking time (50 ft) and the difficulty and pain of performing various activities decreased. Most improvements had occurred after 1 month of PT. For the first time, the effects of a PT program have been quantitatively measured for patients with knee OA.

Effects of a quantitative progressive rehabilitation program applied unilaterally to the osteoarthritic knee

Decreases in muscular strength, endurance, and angular velocity have previously been demonstrated in the elderly. Osteoarthritis (OA), especially of the knee, may cause further reductions in these parameters and lead to functional limitations. This study measured the effects of a quantitative progressive exercise muscle rehabilitation program (QPE) that was added to a physical therapy (PT) program. Forty subjects (20 men and 20 women) with OA of the knees were randomly selected from a group of volunteers (N = 437) for the 3-month program. Measurements of strength, endurance, angular velocity, and the Jette Functional Status Index were determined before and after 1, 2, and 3 months of the program. The QPE program was composed of isometric, isotonic, isotonic with resistance, endurance, and speed contractions prescribed in a progressive sequence. Muscle strength (14% and 29%) and endurance (38% and 43%) increased significantly (p < 0.05, ANOVA for repeated measures) for both the quadriceps and hamstrings, respectively, after rehabilitation. There were marked decreases in walking time and the difficulty and pain experienced during functional activities.

Effect of graded exercise on nitric oxide in expired air in humans

This study was performed to determine the influence of graded dynamic exercise and of voluntary hyperventilation on both the concentration ([NO]) and the amount of nitric oxide per unit time (VNO) in exhaled air. Young human subjects (n = 8) of varying fitness levels having peak O2 consumption (VO2) values ranging between 25.7 and 50.9 ml/min/kg were studied during graded levels of treadmill exercise. Expired [NO] determined by chemiluminescence was 26.3 +/- 6.7 SE parts per billion (ppb) at rest ranging between 11 and 66 ppb. Although variable, [NO] was maintained as work rate increased. VNO rose significantly in most subjects from a mean resting value of 12.3 +/- 3.5 nmol/min. VNO correlated linearly and significantly with ventilation (VE) and CO2 output in 6 of 8 subjects, with VO2 in 4 of 8 subjects, and with heart rate in 5 of 8 subjects. Increases of VNO per unit increase of VE were significantly higher in subjects having higher peak VO2 levels. Voluntary hyperventilation (two-fold of the control VE) for 1 min in 6 subjects decreased expired [NO] from 9.5 (+/- 2.5) to 4.8 (+/- 2.8) ppb and VNO was unchanged, while hyperventilation at 3 x control VE increased VNO by 50% and [NO] decreased to 4.7 +/- 1.8 ppb. VNO appeared to be related to VO2 during hyperventilation. The results suggest that VNO can be correlated with ventilation and heart rate during exercise and with VO2 during both exercise and hyperventilation. [NO] is influenced by the flow rate of the expired air whereas VNO is influenced by NO clearance at the alveolus.

Cardiovascular, respiratory, and metabolic responses to upper body exercise.

Many studies have suggested that arm exercise, particularly in the supine position or with arms elevated, is more stressful than leg exercise. Arm exercise at a given workload is typified by cardiac output and oxygen consumption values slightly higher and heart rate, blood pressure, ventilatory and blood lactic acid responses that are significantly higher than those observed during leg exercise. Part of the increased physiological stress during arm exercise may be due to sluggish kinetics of oxidative metabolism and increased glycolysis leading to lactic acid production and accumulation in blood. This physiological state would lead to a cardiovascular and respiratory pressor effect. The limitations of VO2 adjustment in the arms are not due to cardiac or muscle blood flow limitations as these are quick to adjust and reach higher absolute levels than during leg exercise. Specific arm training increases the VO2 adjustment, and the physiological values in these subjects during arm exercise are similar to those observed during leg exercise.

The underwater environment: cardiopulmonary, thermal, and energetic demands

Water covers over 75% of the earth, has a wide variety of depths and temperatures, and holds a great deal of the earths resources. The challenges of the underwater environment are underappreciated and more short term compared with those of space travel. Immersion in water alters the cardio-endocrine-renal axis as there is an immediate translocation of blood to the heart and a slower autotransfusion of fluid from the cells to the vascular compartment. Both of these changes result in an increase in stroke volume and cardiac output. The stretch of the atrium and transient increase in blood pressure cause both endocrine and autonomic changes, which in the short term return plasma volume to control levels and decrease total peripheral resistance and thus regulate blood pressure. The reduced sympathetic nerve activity has effects on arteriolar resistance, resulting in hyperperfusion of some tissues, which for specific tissues is time dependent. The increased central blood volume results in increased pulmonary artery pressure and a decline in vital capacity. The effect of increased hydrostatic pressure due to the depth of submersion does not affect stroke volume; however, a bradycardia results in decreased cardiac output, which is further reduced during breath holding. Hydrostatic compression, however, leads to elastic loading of the chest wall and negative pressure breathing. The depth-dependent increased work of breathing leads to augmented respiratory muscle blood flow. The blood flow is increased to all lung zones with some improvement in the ventilation-perfusion relationship. The cardiac-renal responses are time dependent; however, the increased stroke volume and cardiac output are, during head-out immersion, sustained for at least hours. Changes in water temperature do not affect resting cardiac output; however, maximal cardiac output is reduced, as is peripheral blood flow, which results in reduced maximal exercise performance. In the cold, maximal cardiac output is reduced and skin and muscle are vasoconstricted, resulting in a further reduction in exercise capacity.

Effect of dietary intake on immune function in athletes.

AbstractAthletes are exposed to acute and chronic stress that may lead to suppression of the immune system and increased oxidative species generation. In addition, the tendency to consume fewer calories than expended and to avoid fats may further compromise the immune system and antioxidant mechanisms. The exercise stress is proportional to the intensity and duration of the exercise, relative to the maximal capacity of the athlete. Muscle glycogen depletion compromises exercise performance and it also increases the stress. Glycogen stores can be protected by increased fat oxidation (glycogen sparing). The diets of athletes should be balanced so that total caloric intake equals expenditure, and so that the carbohydrates and fats utilised in exercise are replenished. Many athletes do not meet these criteria and have compromised glycogen or fat stores, have deficits in essential fats, and do not take in sufficient micronutrients to support exercise performance, immune competence and antioxidant defence. Either over-training or under nutrition may lead to an increased risk of infections. Exercise stress leads to a proportional increase in stress hormone levels and concomitant changes in several aspects of immunity, including the following: high cortisol; neutrophilia; lymphopenia; decreases in granulocyte oxidative burst, nasal mucociliary clearance, natural killer cell activity, lymphocyte proliferation, the delayed-type sensitivity response, the production of cytokines in response to mitogens, and nasal and salivary immunoglobulin A levels; blunted major histocompatibility complex II expression in macrophages; and increases in blood granulocyte and monocyte phagocytosis, and pro-and anti-inflammatory cytokines. In addition to providing fuel for exercise, glycolysis, glutaminlysis, fat oxidation and protein degradation participate in metabolism and synthesis of the immune components. Compromising, or overusing, any of these components may lead to immunosuppression. In some cases, supplementation with micronutrients may facilitate the immune system and compensate for deficits in essential nutrients. In summary, athletes should eat adequate calories and nutrients to balance expenditure of all nutrients. Dietary insufficiencies should be compensated for by supplementation with nutrients, with care not to over compensate. By following these rules, and regulating training to avoid overtraining, the immune system can be maintained to minimise the risk of upper respiratory tract infections.

Energetics of swimming: a historical perspective

The energy cost to swim a unit distance (Csw) is given by the ratio

Heart rate variability during dynamic exercise in elderly males and females.

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