Jochen Kressler

Reducing Cardiometabolic Disease in Spinal Cord Injury

Accelerated cardiometabolic disease is a serious health hazard after spinal cord injuries (SCI). Lifestyle intervention with diet and exercise remains the cornerstone of effective cardiometabolic syndrome treatment. Behavioral approaches enhance compliance and benefits derived from both diet and exercise interventions and are necessary to assure that persons with SCI profit from intervention. Multitherapy strategies will likely be needed to control challenging component risks, such as gain in body mass, which has far reaching implications for maintenance of daily function as well as health.

Sildenafil Has Little Influence on Cardiovascular Hemodynamics or 6-km Time Trial Performance in Trained Men and Women at Simulated High Altitude

UNLABELLED Sildenafil improves maximal exercise capacity at high altitudes (∼4350-5800 m) by reducing pulmonary arterial pressure and enhancing oxygen delivery, but the effects on exercise performance at less severe altitudes are less clear. PURPOSE To determine the effects of sildenafil on cardiovascular hemodynamics (heart rate, stroke volume, and cardiac output), arterial oxygen saturation (SaO2), and 6-km time-trial performance of endurance-trained men and women at a simulated altitude of ∼3900 m. METHODS Twenty men and 15 women, endurance-trained, completed one experimental exercise trial (30 min at 55% of altitude-specific capacity +6-km time trial) at sea level (SL) and two trials at simulated high altitude (HA) while breathing hypoxic gas (12.8% FIo2) after ingestion of either placebo or 50 mg sildenafil in double-blind, randomized, and counterbalanced fashion. RESULTS Maximal exercise capacity and SaO2 were significantly reduced at HA compared to SL (18%-23%), but sildenafil did not significantly improve cardiovascular hemodynamics or time-trial performance in either men or women compared to placebo and only improved SaO2 in women (4%). One male subject (5% of male subjects, 2.8% of all subjects) exhibited a meaningful 36-s improvement in time-trial performance with sildenafil compared to placebo. CONCLUSIONS In this group of endurance trained men and women, sildenafil had very little influence on cardiovascular hemodynamics, SaO2, and 6-km time-trial performance at a simulated altitude of ∼3900 m. It appears that a very small percentage of endurance-trained men and women derive meaningful improvements in aerobic performance from sildenafil at a simulated altitude of ∼3900 m.

Reference Fitness Values in the Untrained Spinal Cord Injury Population

OBJECTIVE Establish reference values of cardiorespiratory fitness applicable to the general, untrained spinal cord injury (SCI) population. DESIGN Data were retroactively obtained from 12 studies (May 2004 to May 2012). SETTING An institution-affiliated applied physiology research laboratory. PARTICIPANTS A total of 153 men and 26 women (age, 18-55y) with chronic SCI (N=179) were included. Participants were not involved in training activities for 1 or more months before testing and were able to complete a progressive resistance exercise test to determine peak oxygen consumption (Vo2peak). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURE Percentile ranking (poor<20%; fair; 20%-40%; average, 40%-60%; good, 60%-80%; excellent, 80%-100%) used to establish reference values. RESULTS Reference cardiorespiratory fitness values based on functional classification as paraplegic or tetraplegic were established (paraplegic: median, 16.0mL·kg(-1)·min(-1); range, 1.4-35.2mL·kg(-1)·min(-1); tetraplegic: median, 8.8mL·kg(-1)·min(-1); range, 1.5-21.5mL·kg(-1)·min(-1)) for untrained men and women. For the primary outcome measure (Vo2peak), persons with paraplegia had significantly higher values than did persons with tetraplegia (P<.001). Although men had higher values than did women, these differences did not reach significance (P=.256). Regression analysis revealed that motor level of injury was associated with 22.3% of the variability in Vo2peak (P<.001), and an additional 8.7% was associated with body mass index (P<.001). No other measure accounted for additional significant variability. CONCLUSIONS Established reference fitness values will allow investigators/clinicians to stratify the relative fitness of subjects/patients from the general SCI population. Key determinants are motor level of injury and body habitus, yet most variability in aerobic capacity is not associated with standard measures of SCI status or demographic characteristics.

Ischemic preconditioning does not improve peak exercise capacity at sea level or simulated high altitude in trained male cyclists

Ischemic preconditioning (IPC) may improve blood flow and oxygen delivery to tissues, including skeletal muscle, and has the potential to improve intense aerobic exercise performance, especially that which results in arterial hypoxemia. The aim of the study was to determine the effects of IPC of the legs on peak exercise capacity (W(peak)), submaximal and peak cardiovascular hemodynamics, and peripheral capillary oxygen saturation (SpO2) in trained males at sea level (SL) and simulated high altitude (HA; 13.3% FIO2, ∼ 3650 m). Fifteen highly trained male cyclists and triathletes completed 2 W(peak) tests (SL and HA) and 4 experimental exercise trials (10 min at 55% altitude-specific W(peak) then increasing by 30 W every 2 min until exhaustion) with and without IPC. HA resulted in significant arterial hypoxemia during exercise compared with SL (73% ± 6% vs. 93% ± 4% SpO2, p < 0.001) that was associated with 21% lower W(peak) values. IPC did not significantly improve W(peak) at SL or HA. Additionally, IPC failed to improve cardiovascular hemodynamics or SpO2 during submaximal exercise or at W(peak). In conclusion, IPC performed 45 min prior to exercise does not improve W(peak) or systemic oxygen delivery during submaximal or peak exercise at SL or HA. Future studies must examine the influence of IPC on local factors, such as working limb blood flow, oxygen delivery, and arteriovenous oxygen difference as well as whether the effectiveness of IPC is altered by the volume of muscle made ischemic, the timing prior to exercise, and high altitude acclimatization.

Heavy reliance on carbohydrate across a wide range of exercise intensities during voluntary arm ergometry in persons with paraplegia.

Abstract Context/objective To describe and compare substrate oxidation and partitioning during voluntary arm ergometry in individuals with paraplegia and non-disabled individuals over a wide range of exercise intensities. Design Cross-sectional study. Setting Clinical research facility. Participants Ten apparently healthy, sedentary men with paraplegia and seven healthy, non-disabled subjects. Interventions Rest and continuous progressive voluntary arm ergometry between 30 and 80% of peak aerobic capacity (VO2peak). Outcome measures Total energy expenditure and whole body rates of fat and carbohydrate oxidation. Results A maximal whole body fat oxidation (WBFO) rate of 0.13 ± 0.07 g/minute was reached at 41 ± 9% VO2peak for subjects with paraplegia, although carbohydrate became the predominant fuel source during exercise exceeding an intensity of 30–40% VO2peak. Both the maximal WBFO rate (0.06 ± 0.04 g/minute) and the intensity at which it occurred (13 ± 3% VO2peak) were significantly lower for the non-disabled subjects than those with paraplegia. Conclusion Sedentary individuals with paraplegia are more capable of oxidizing fat during voluntary arm ergometry than non-disabled individuals perhaps due to local adaptations of upper body skeletal muscle used for daily locomotion. However, carbohydrate is the predominant fuel source oxidized across a wide range of intensities during voluntary arm ergometry in those with paraplegia, while WBFO is limited and maximally achieved at low exercise intensities compared to that achieved by able-bodied individuals during leg ergometry. These findings may partially explain the diminished rates of fat loss imposed by acute bouts of physical activity in those with paraplegia.

Circuit training and protein supplementation in persons with chronic tetraplegia

UNLABELLED Circuit resistance training (CRT) performed three times weekly for 40-45 min each session increases muscular strength and both aerobic and anaerobic capacity in untrained individuals with chronic paraplegia. Whether similar CRT is also effective for conditioning of persons with chronic tetraplegia is unknown. In addition, protein supplementation (PS) before and immediately postexercise has been shown to enhance exercise adaptations. PURPOSE This study aimed to investigate whether a modified 40-45 min CRT program will improve fitness attributes in individuals with tetraplegia and whether these changes are enhanced by PS. METHODS Eleven individuals with chronic tetraplegia underwent 6 months of CRT performed three times per week. Six randomly assigned participants received PS (whey protein = 36-37 g) in split doses immediately before and after exercise sessions. Others consumed a matched protein dose 24 h postexercise. Measurements of one-repetition maximum (1-RM) strength for six different resistance exercises, arm peak oxygen consumption (VO2peak), and arm anaerobic power (Wingate) were obtained 3 months before (-3mo), at the beginning (0mo), 3 months into (3mo), and 6 months after (6mo) the beginning of CRT. RESULTS One-repetition maximum increased by 8%-11% ± 6%-12% for each successive 3-month period (P ≤ 0.001-0.012), independent of PS group (P = 0.105). VO2peak increased significantly from 0mo to 6mo with immediate PS (35% ± 29%, P = 0.020) but failed to reach significance for delayed PS (15% ± 8%, P = 0.147). Power drop changes during the Wingate test were also only significant for the immediate PS (median difference 40W, P = 0.028) and not for delayed (10W, P = 0.500). CONCLUSION CRT effectively increased muscular strength, aerobic capacity, and anaerobic fatigue resistance in persons with chronic tetraplegia. The latter two conditioning benefits were further enhanced by timely PS.

Physiological responses to exergaming after spinal cord injury.

PURPOSE To investigate whether exergaming satisfies guideline-based intensity standards for exercise conditioning (40%/50% oxygen uptake reserve [VO2R] or heart rate reserve (HRR), or 64%/70% of peak heart rate [HRpeak]) in persons with paraplegia. METHODS Nine men and women (18-65 years old) with chronic paraplegia (T1-L1, AIS A-C) underwent intensity-graded arm cycle exercise (AE) to evaluate VO2peak and HRpeak. On 2 randomized nonconsecutive days, participants underwent graded exercise using a custom arm cycle ergometer that controls the video display of a Nintendo Gamecube (GameCycle; Three Rivers Holdings LLC, Mesa, AZ) or 15 minutes of incrementally wrist-weighted tennis gameplay against a televised opponent (XaviX Tennis System; SSD Co Ltd, Kusatsu, Japan). RESULTS GameCycle exergaming (GCE) resistance settings ≥0.88 Nm evoked on average ≥50% VO2R. During XaviX Tennis System exergaming (XTSE) with wrist weights ≥2 lbs, average VO2 reached a plateau of ~40% VO2R. Measurements of HR were highly variable and reached average values ≥50% HRR during GCE at resistance settings ≥0.88 Nm. During XTSE, average HR did not reach threshold levels based on HRR for any wrist weight (20%-35% HRR). CONCLUSIONS On average, intensity responses to GCE at resistance setting ≥0.88 Nm were sufficient to elicit exercise intensities needed to promote cardiorespiratory fitness in individuals with SCI. The ability of XTSE to elicit cardiorespiratory fitness benefits is most likely limited to individuals with very low fitness levels and may become subminimal with time if used as a conditioning stimulus.

Subjective measures of exercise intensity to gauge substrate partitioning in persons with paraplegia.

BACKGROUND The Borg Rating of Perceived Exertion (RPE) Scale and talk test (TT) are commonly recommended for persons to gauge exercise intensity. It is not known whether they are suitable to estimate substrate partitioning between carbohydrate and fat in persons with SCI. OBJECTIVE Investigate substrate partitioning/utilization patterns associated with RPE and TT. METHODS Twelve participants with chronic paraplegia underwent 2 arm crank exercise tests on nonconsecutive days within 2 weeks. Test 1 was a graded exercise test (GXT) to volitional exhaustion. Test 2 was a 15-minute self-selected steady state (SS) voluntary arm exercise bout simulating a brief, yet typical exercise session. RESULTS For the GXT, very light intensity exercise (RPE < 9) and TT stage before last positive were associated with highest contribution of fat oxidation (~35%-50%) to total energy expenditure (TEE). Fat oxidation was low at all stages, with the highest rate (0.13 ± 0.07 g/min) occurring at stage 1 (10 W). Corresponding average RPE was 7 ± 2 and the TT was positive for all participants at this stage. For the SS, fuel partitioning throughout exercise was dominated by carbohydrate oxidation (1.47 ± 0.08 g/min), accounting for almost all (~94%) of TEE with only a minute contribution from fat oxidation (0.02 ± 0.004 g/min). A positive TT was associated with an average contribution of fat oxidation of ~10%. CONCLUSIONS RPE but not the TT appears suitable to predict exercise intensities associated with the highest levels of fat oxidation. However, such intensities are below authoritative intensity thresholds for cardiorespiratory fitness promotion, and therefore the applicability of such a prediction for exercise prescriptions is likely limited to individuals with low exercise tolerance.

Effects of prandial challenge on triglyceridemia, glycemia, and pro-inflammatory activity in persons with chronic paraplegia

Abstract Context/Objective Exaggerated postprandial lipemia has been reported after spinal cord injury (SCI). We examined metabolite and accompanying pro-inflammatory biomarker responses to repeat feeding of typical high-fat meals in individuals with chronic paraplegia. Design Descriptive trial. Methods Metabolites (triglycerides, glucose, and insulin) and inflammatory biomarkers (interleukin-6 and high-sensitivity C-reactive protein (hsCRP)) were measured under fasting conditions in 11 recreationally active individuals with chronic (>1 year) paraplegia. Subjects received high-fat meals at time point 0 and again at minute 240. Antecubital venous blood was obtained at time points −30 (fasting), 0 (first meal), 30, 60, 90, 120, 240 (second meal), 360, and 480 minutes. Correlations were examined among the study variables. Exploratory subgroup analysis was performed for subjects with levels of postprandial glucose greater than >200 mg/dl. Results Triglycerides showed a significant rise 4 hours after eating. Basal inflammatory markers were elevated, and did not undergo additional change during the testing. Additionally, subjects with excessive postprandial glucose responses showed higher hsCRP levels than those having typical glucose responses both for fasting (11.8 ± 6.5 vs. 2.9 ± 2.7 mg/l, P = 0.064) and postprandial (11.1 ± 4.9 vs. 3.7 ± 3.8 mg/l, P = 0.018) values. Conclusions Despite elevations in metabolic response markers, inflammatory markers did not change significantly after consumption of population-representative (i.e. hypercaloric) mixed-nutrient meals. Levels of fasting CRP in the high-risk range are consistent with other reports in persons with SCI and continue to pose concern for their cardiovascular disease risk. The possible association between postprandial metabolic responses and inflammatory states warrants further investigation to identify individual component risks for this secondary health hazard.

Effects of Circuit Resistance Training and Timely Protein Supplementation on Exercise-Induced Fat Oxidation in Tetraplegic Adults

BACKGROUND Substrate utilization during exercise in persons with spinal cord injury (SCI) remains poorly defined. PURPOSE To investigate effects of circuit resistance training (CRT) and timing of protein supplementation (PS) on fuel utilization in persons with tetraplegia. METHODS Eleven individuals with chronic tetraplegia underwent 6 months of CRT 3 times weekly. Five randomly assigned participants received immediate PS (iPS) administered in split doses prior to and following all exercise sessions. Other participants consumed a matched dose of PS that was delayed until 24 hours post-exercise (dPS). Participants underwent a maximal graded exercise test (GXT) to volitional exhaustion at 4 conditioning time points: 3 months before (-3mo), at the beginning of (0mo), 3 months into (3mo), and 6 months following (6mo) the CRT conditioning program. Respiratory measures were continuously obtained throughout the GXT via open-circuit spirometry. Fuel utilization and energy expenditure were computed from the respiratory data. RESULTS The differences in changes in substrate utilization between the PS groups were not significant as determined by the interaction of PS group and conditioning time point, F (3, 27) = 2.32, P = .098, η(2) P = .205. Maximal absolute fat oxidation did not change significantly from 0 to 6mo (mean difference, 0.014 ± 0.031 g/min; P = .170), and fat oxidation remained low never exceeding an average of 0.10 ± 0.09 g/min for any given exercise intensity. CONCLUSION Maximum fat utilization during exercise and fat utilization at matched exercise intensities were not increased in persons with tetraplegia, independent of PS, and levels of fat oxidation remained low after training.