Diurnal variation of heart rate variability in individuals with spinal cord injury.

BACKGROUND: Heart rate variability (HRV) may provide objective information about cardiogenic autonomic balance in individuals with spinal cord injury (SCI). The aim of this study was to characterize the diurnal variation of HRV in individuals with SCI at lesion level T6 and above and lesion level below T6. METHODS: This was a retrospective analysis of a prior cross-sectional study. Individuals with chronic SCI underwent 24 h recording of the time between consecutive R waves (RR interval) to derive parameters of HRV as follows: standard deviation of all normal-to-normal R-R intervals (SDNN) and square root of the mean of the squared differences between successive R-R intervals (RMSSD) (time domain); and high frequency power (HF), low-frequency power (LF), very low frequency power (VLF), ultra-low frequency power (ULF) and total power (TP) (frequency domain). Changes in the magnitude of HRV outcomes over the 24 h period were investigated using a novel multi-component cosinor model constrained to the form of a three-harmonic Fourier series. RESULTS: Participants were grouped as lesion level T6 and above (n = 22) or below T6 (n = 36). Most of them were male (n = 40, 69%) and the median age (interquartile range) was 50.5 (28) years. Both groups exhibited similar diurnal patterns in most HRV metrics. The lowest values occurred in the late afternoon (4-6 pm) and gradually increased, peaking around midnight to early morning (1-6 am). Exceptions included RMSSD, which peaked before midnight, and ULF, which showed a double peak pattern that peaked from 11 am to 1 pm and 4-6 am in participants with lesion level at T6 and above. The HRV values in participants with lesion level T6 and above were generally lower than participants with lesion level below T6, except for peak values of RMSSD, HF and LF. CONCLUSION: This study demonstrated substantial diurnal variation of HRV in participants with SCI in both groups of participants. In clinical and research settings, diurnal variations in HRV must be taken into consideration.

Test-retest reliability of short- and long-term heart rate variability in individuals with spinal cord injury.

STUDY DESIGN: Cross-sectional. OBJECTIVES: To investigate test-retest reliability of heart rate variability (HRV) metrics in SCI without restriction of activity over long (24-h) and shorter durations (5-min, 10-min, 1-h, 3-h and 6-h). SETTINGS: University hospital in Khon Kaen, Thailand. METHODS: Forty-five participants (11 with tetraplegia and 34 with paraplegia) underwent two 24-h recordings of RR-intervals to derive time and frequency HRV metrics. Relative reliability was assessed by intraclass correlation coefficient (ICC) and absolute reliability by coefficient of variation (CV) and Bland-Altman limits of agreement (LoA). RESULTS: For 5- and 10-min durations, eight of eleven HRV metrics had moderate to excellent reliability (ICC 0.40-0.76); the remaining three were poor (ICC < 0.4). HRV values from 1-h and 3-h durations showed moderate to excellent reliability (ICC of 0.46-0.81), except for 1-h reliability of ULF and TP (ICC of 0.06 and 0.30, respectively). Relative reliability was excellent (ICC of 0.77-0.92) for 6-h and 24-h durations in all HRV metrics. Absolute reliability improved as recording duration increased (lower CVs and narrower LoAs). Participants with high AD risk (SCI level at or above T6) showed lower test-retest reliability of HF and LF values than participants with low AD risk. CONCLUSION: Relative reliability of HRV was excellent for 6-h and 24-h. The best absolute reliability values were for 24-h duration. Time-domain outcomes were more reliable than frequency domain outcomes. Participants with high risk of AD, particularly those with tetraplegia, showed lower reliability, especially for HF and LF.

Identification of heart rate dynamics during treadmill exercise: comparison of first- and second-order models.

BACKGROUND: Characterisation of heart rate (HR) dynamics and their dependence on exercise intensity provides a basis for feedback design of automatic HR control systems. This work aimed to investigate whether the second-order models with separate Phase I and Phase II components of HR response can achieve better fitting performance compared to the first-order models that do not delineate the two phases. METHODS: Eleven participants each performed two open-loop identification tests while running at moderate-to-vigorous intensity on a treadmill. Treadmill speed was changed as a pseudo-random binary sequence (PRBS) to excite both the Phase I and Phase II components. A counterbalanced cross-validation approach was implemented for model parameter estimation and validation. RESULTS: Comparison of validation outcomes for 22 pairs of first- and second-order models showed that root-mean-square error (RMSE) was significantly lower and fit (normalised RMSE) significantly higher for the second-order models: RMSE was 2.07 bpm ± 0.36 bpm vs. 2.27 bpm ± 0.36 bpm (bpm = beats per min), second order vs. first order, with [Formula: see text]; fit was [Formula: see text]% vs. [Formula: see text]%, [Formula: see text]. CONCLUSION: Second-order models give significantly better goodness-of-fit than first-order models, likely due to the inclusion of both Phase I and Phase II components of heart rate response. Future work should investigate alternative parameterisations of the PRBS excitation, and whether feedback controllers calculated using second-order models give better performance than those based on first-order models.

Dynamic Loading Assessment at the Fifth Metatarsal in Elite Athletes With a History of Jones Fracture.

OBJECTIVE: We hypothesize that athletes who have suffered Jones fractures will apply significantly higher loads at the fifth metatarsal base during athletic activities compared with matched uninjured athletes. DESIGN: Sixteen athletes were recruited to participate. Eight athletes had a history of Jones fracture, and 8 age, gender, and position-matched athletes without a history of foot injury were recruited as controls. SETTING: Institutional study at Stanford University. PARTICIPANTS: Sixteen athletes with/without a history of foot injury from Stanford University. INTERVENTIONS: Athletes performed a standardized series of movements while wearing calibrated, wireless pressure mapping insoles, and then again with their custom corrective insoles. MAIN OUTCOME MEASURES: Peak pressure, mean pressure, maximum force, and force-time integral (ie, impulse) were recorded for each activity. RESULTS: Athletes with a history of Jones fracture showed a significantly increased peak pressure (183 ± 23 vs 138 ± 7 kPA), mean pressure (124 ± 14 vs 95 ± 4 kPA), and maximum force (15 ± 1.2 vs 12 ± 1.2%BW) at the fifth metatarsal base during walking and running compared with uninjured matched controls (all P < 0.05). CONCLUSIONS: Athletes with a history of Jones fracture exert significantly increased peak and mean forces at the base of the fifth metatarsal during common athletic activities. Custom orthoses do not seem to offload this region in all cases. Increased loads may contribute to the development of stress injury to the fifth metatarsal during repetitive loading, and ultimately fracture of the bone.

Editorial Commentary: Living in the Material World: Could Viscoelastic Properties of Sutures Impact Patient Outcomes?

The viscoelastic properties of suture may impact how soft tissue (such as the shoulder rotator cuff tendons) heals to bone and therefore may impact patient outcomes. Thus, it is logical to use suture material less likely to creep and elongate. Suture tape, in particular, may show superior biomechanical properties compared with standard sutures. However, in cadaveric studies, failure generally occurs at the tissue interface, rather than the suture material (or anchor). Thus, the quality and thickness of local tissue must be taken into consideration when determining postoperative rehabilitation or return to activity. Clinical outcome studies comparing suture materials remain elusive, but there is little reason not to use stronger suture material, and this is an option within the surgeon's control.

The CFL fails before the ATFL immediately after combined ligament repair in a biomechanical cadaveric model.

PURPOSE: To assess the impact on ankle stability after repairing the ATFL alone compared to repairing both the ATFL and CFL in a biomechanical cadaver model. METHODS: Ten matched pairs of intact, fresh frozen human cadaver ankles (normal) were mounted to a test machine in 20.0° plantar flexion and 15.0° of internal rotation. Each ankle was loaded to body weight and then tested from 0.0° to 20.0° of inversion. The data recorded were torque at 20.0° and stiffness, peak pressure and contact area in the ankle joint using a Tekscan sensor, rotation of the talus and calcaneus, and translation of the calcaneus using a three-dimensional motion capture system. Ankles then underwent sectioning of the ATFL and CFL (injured), retested, then randomly assigned to ATFL-only Broström repair or combined ATFL and CFL repair. Testing was repeated after repair then loaded in inversion to failure (LTF). RESULTS: The stiffness of the ankle was not significantly increased compared to the injured condition by repairing the ATFL only (n.s.) or the ATFL/CFL (n.s.). The calcaneus had significantly more rotation than the injured condition in the ATFL-only repair (p = 0.037) but not in the ATFL/CFL repair (n.s.). The ATFL failed at 40.3% higher torque than the CFL, at 17.4 ± 7.0 N m and 12.4 ± 4.1 N m, respectively, and 62.0% more rotation, at 43.9 ± 5.6° and 27.1 ± 6.8°, respectively. CONCLUSIONS: There was a greater increase in stiffness following combined ATFL/CFL repair compared to ATFL-only repair, although this did not reach statistical significance. The CFL fails before the ATFL, potentially indicating its vulnerability immediately following repair. LEVEL OF EVIDENCE: III, case-control therapeutic study.

Stimulation of paralysed quadriceps muscles with sequentially and spatially distributed electrodes during dynamic knee extension.

BACKGROUND: During functional electrical stimulation (FES) tasks with able-bodied (AB) participants, spatially distributed sequential stimulation (SDSS) has demonstrated substantial improvements in power output and fatigue properties compared to conventional single electrode stimulation (SES). The aim of this study was to compare the properties of SDSS and SES in participants with spinal cord injury (SCI) in a dynamic isokinetic knee extension task simulating knee movement during recumbent cycling. METHOD: Using a case-series design, m. vastus lateralis and medialis of four participants with motor and sensory complete SCI (AIS A) were stimulated for 6 min on both legs with both electrode setups. With SES, target muscles were stimulated by a pair of electrodes. In SDSS, the distal electrodes were replaced by four small electrodes giving the same overall stimulation frequency and having the same total surface area. Torque was measured during knee extension by a dynamometer at an angular velocity of 110 deg/s. Mean power of the left and right sides (PmeanL,R) was calculated from all stimulated extensions for initial, final and all extensions. Fatigue is presented as an index value with respect to initial power from 1 to 0, whereby 1 means no fatigue. RESULTS: SDSS showed higher PmeanL,R values for all four participants for all extensions (increases of 132% in participant P1, 100% in P2, 36% in P3 and 18% in P4 compared to SES) and for the initial phase (increases of 84%, 59%, 66%, and 16%, respectively). Fatigue resistance was better with SDSS for P1, P2 and P4 but worse for P3 (0.47 vs 0.35, 0.63 vs 0.49, 0.90 vs 0.82 and 0.59 vs 0.77, respectively). CONCLUSION: Consistently higher PmeanL,R was observed for all four participants for initial and overall contractions using SDSS. This supports findings from previous studies with AB participants. Fatigue properties were better in three of the four participants. The lower fatigue resistance with SDSS in one participant may be explained by a very low muscle activation level in this case. Further investigation in a larger cohort is warranted.

Postoperative Imaging of the Ankle.

OBJECTIVE: The purpose of this article is to review imaging after commonly encountered surgical interventions of the ligaments, tendons, and soft tissues around the ankle. Intraoperative images, when available, are provided to improve conceptual understanding of these complex procedures. CONCLUSION: Surgical interventions in the ankle are becoming more prevalent with increasing athletic demands and emerging focus on techniques for prevention of joint injury. Knowledge of the surgical techniques, imaging appearances, and complications in the postoperative ankle is necessary for the accurate diagnosis of postoperative complications and for optimal patient care.

Changes in heart rate variability with respect to exercise intensity and time during treadmill running.

BACKGROUND: Heart rate variability (HRV) arises from the complex interplay of sympathetic and parasympathetic autonomic regulation of heart rate. Ultra-low frequency (ULF) and very-low frequency (VLF) components of HRV play a crucial role in automatic HR controllers, but these frequency bands have hitherto largely been neglected in HRV studies. The aim of this work was to investigate changes in ULF and VLF heart rate variability with respect to exercise intensity and time during treadmill running. METHODS: RR intervals were determined by ECG in 21 healthy male participants at rest, and during moderate and vigorous-intensity treadmill running; each of these three tests had a duration of 45 min. Time dependence of HRV was investigated for moderate and vigorous running intensities by dividing the constant-speed stages into three consecutive windows of equal duration ([Formula: see text] 14 min), denoted [Formula: see text], [Formula: see text] and [Formula: see text]. ULF and VLF power were computed using Lomb-Scargle power spectral density estimates. RESULTS: For both the ULF and VLF frequency bands, mean power was significantly different between the resting, moderate and vigorous intensity levels (overall [Formula: see text]): mean power was lower for moderate vs. rest ([Formula: see text]), for vigorous vs. rest ([Formula: see text]), and for vigorous vs. moderate ([Formula: see text]). For both ULF and VLF and moderate intensity, mean power was significantly different between the three time windows (overall [Formula: see text] for ULF, overall [Formula: see text] for VLF): for ULF, mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]) and for [Formula: see text] vs. [Formula: see text] ([Formula: see text]); for VLF, mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]). For ULF and vigorous intensity, there was no significant difference in mean power between the three time windows (overall [Formula: see text]). For VLF and vigorous intensity, mean power was significantly different between [Formula: see text], [Formula: see text] and [Formula: see text] (overall [Formula: see text]): mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]) and for [Formula: see text] vs. [Formula: see text] ([Formula: see text]). CONCLUSIONS: The degree of HRV in terms of ULF and VLF power was found to decrease with increasing intensity of exercise. HRV was also observed to decrease over time, but it remains to clarify whether these changes are due to time itself or to increases in HR related to cardiovascular drift. For feedback control applications, attention should be focused on meeting performance targets at low intensity and during the early stages of exercise.

Power output and fatigue properties using spatially distributed sequential stimulation in a dynamic knee extension task.

PURPOSE: The low power output and fatigue resistance during functional electrical stimulation (FES) limits its use for functional applications. The aim of this study was to compare the power output and fatigue properties of spatially distributed sequential stimulation (SDSS) against conventional single electrode stimulation (SES) in an isokinetic knee extension task simulating knee movement during recumbent cycling. METHODS: M. vastus lateralis and m. vastus medialis of eight able-bodied subjects were stimulated for 6 min on both legs with both setups. In the SES setup, target muscles were each stimulated by a pair of electrodes. In SDSS, four small electrodes replaced the SES active electrodes, but reference electrodes were the same. Torque was measured during knee extension movement by a dynamometer at an angular velocity of 110°/s. Mean power (P mean) was calculated from stimulated extensions for the first 10 extensions, the final 20 extensions and overall. Fatigue is presented as an index, calculated as the decrease with respect to initial power. RESULTS: P mean was significantly higher for SDSS than for SES in the final phase (9.9 ± 4.0 vs. 7.4 ± 4.3 W, p = 0.035) and overall (11.5 ± 4.0 vs. 9.2 ± 4.5 W, p =  0.037). With SDSS, the reduction in P mean was significantly smaller compared to SES (from 14.9 to 9.9 vs. 14.6 to 7.4 W, p = 0.024). The absolute mean pulse width was substantially lower with SDSS (62.5 vs. 90.0 µs). CONCLUSION: Although less stimulation was applied, SDSS showed a significantly higher mean power output than SES. SDSS also had improved fatigue resistance when compared to conventional stimulation. The SDSS approach may provide substantial performance benefits for cyclical FES applications.

Test-retest reliability and four-week changes in cardiopulmonary fitness in stroke patients: evaluation using a robotics-assisted tilt table.

BACKGROUND: Exercise testing devices for evaluating cardiopulmonary fitness in patients with severe disability after stroke are lacking, but we have adapted a robotics-assisted tilt table (RATT) for cardiopulmonary exercise testing (CPET). Using the RATT in a sample of patients after stroke, this study aimed to investigate test-retest reliability and repeatability of CPET and to prospectively investigate changes in cardiopulmonary outcomes over a period of four weeks. METHODS: Stroke patients with all degrees of disability underwent 3 separate CPET sessions: 2 tests at baseline (TB1 and TB2) and 1 test at follow up (TF). TB1 and TB2 were at least 24 h apart. TB2 and TF were 4 weeks apart. A RATT equipped with force sensors in the thigh cuffs, a work rate estimation algorithm and a real-time visual feedback system was used to guide the patients' exercise work rate during CPET. Test-retest reliability and repeatability of CPET variables were analysed using paired t-tests, the intraclass correlation coefficient (ICC), the coefficient of variation (CoV), and Bland and Altman limits of agreement. Changes in cardiopulmonary fitness during four weeks were analysed using paired t-tests. RESULTS: Seventeen sub-acute and chronic stroke patients (age 62.7 ± 10.4 years [mean ± SD]; 8 females) completed the test sessions. The median time post stroke was 350 days. There were 4 severely disabled, 1 moderately disabled and 12 mildly disabled patients. For test-retest, there were no statistically significant differences between TB1 and TB2 for most CPET variables. Peak oxygen uptake, peak heart rate, peak work rate and oxygen uptake at the ventilatory anaerobic threshold (VAT) and respiratory compensation point (RCP) showed good to excellent test-retest reliability (ICC 0.65-0.94). For all CPET variables, CoV was 4.1-14.5 %. The mean difference was close to zero in most of the CPET variables. There were no significant changes in most cardiopulmonary performance parameters during the 4-week period (TB2 vs TF). CONCLUSIONS: These findings provide the first evidence of test-retest reliability and repeatability of the principal CPET variables using the novel RATT system and testing methodology, and high success rates in identification of VAT and RCP: good to excellent test-retest reliability and repeatability were found for all submaximal and maximal CPET variables. Reliability and repeatability of the main CPET parameters in stroke patients on the RATT were comparable to previous findings in stroke patients using standard exercise testing devices. The RATT has potential to be used as an alternative exercise testing device in patients who have limitations for use of standard exercise testing devices.

Identification of heart rate dynamics during moderate-to-vigorous treadmill exercise.

BACKGROUND: Heart rate can be used to prescribe exercise intensity for development and maintenance of cardiorespiratory fitness. The aim of this study was to identify the dynamics of heart rate response during moderate-to-vigorous treadmill exercise and to explore parameter dependencies with respect to time, intensity level and step-change direction. The focus was on simple approximate models for subsequent design of heart rate control systems. METHODS: 24 healthy, able-bodied male subjects each did two separate, 35-min tests on a treadmill, one at moderate and one at vigorous intensity. Each test had four individual upward and downward steps (1-4). Heart rate responses were modelled as first-order transfer functions with steady-state gain k and time constant [Formula: see text]. Models were estimated both for the overall testing periods and for individual step responses within each test. RESULTS: There were no significant differences in the overall mean values of k [24.3 vs. 24.1 bpm/(m/s), [Formula: see text]] and [Formula: see text] (55.7 vs. 59.5 s, [Formula: see text]) between the two intensity levels. The overall nominal gain for both conditions was [Formula: see text], 21.9-26.6 bpm/(m/s) (mean [Formula: see text] standard deviation, 95 % confidence interval), and the overall nominal time constant was [Formula: see text], 50.9-64.3 s. Analysis of models estimated from the individual steps revealed a significant difference in steady-state gain k for upward and downward steps [30.2 vs. 23.6 bpm/(m/s), [Formula: see text]], but no difference in time constant [Formula: see text] between these two directions (57.5 vs. 54.4 s, [Formula: see text]). For gain k, there was no significant main effect of intensity ([Formula: see text]) or intensity-time ([Formula: see text]) interactions, but there was a significant main effect of time ([Formula: see text]). Pairwise comparison with respect to time showed a significant difference between the upward steps at times 1 and 3 [33.0 vs. 27.3 bpm/(m/s), [Formula: see text]], but no significant difference between the downward steps at times 2 and 4 [24.4 vs. 22.8 bpm/(m/s), [Formula: see text]]. For time constant [Formula: see text], there were no significant main effects of intensity ([Formula: see text]) or time ([Formula: see text]), or intensity-time interactions ([Formula: see text]). CONCLUSIONS: The tight CI-bounds obtained, and the observed parameter dependencies, suggest that the overall nominal model with [Formula: see text] and [Formula: see text] might serve as the basis for design of a linear time-invariant (LTI) feedback system for real-time control of heart rate. Future work should focus on this hypothesis and on direct comparison of LTI and nonlinear/time-varying control approaches.

Submaximal cardiopulmonary thresholds on a robotics-assisted tilt table, a cycle and a treadmill: a comparative analysis.

BACKGROUND: The robotics-assisted tilt table (RATT), including actuators for tilting and cyclical leg movement, is used for rehabilitation of severely disabled neurological patients. Following further engineering development of the system, i.e. the addition of force sensors and visual bio-feedback, patients can actively participate in exercise testing and training on the device. Peak cardiopulmonary performance parameters were previously investigated, but it also important to compare submaximal parameters with standard devices. The aim of this study was to evaluate the feasibility of the RATT for estimation of submaximal exercise thresholds by comparison with a cycle ergometer and a treadmill. METHODS: 17 healthy subjects randomly performed six maximal individualized incremental exercise tests, with two tests on each of the three exercise modalities. The ventilatory anaerobic threshold (VAT) and respiratory compensation point (RCP) were determined from breath-by-breath data. RESULTS: VAT and RCP on the RATT were lower than the cycle ergometer and the treadmill: oxygen uptake (V'O2) at VAT was [mean (SD)] 1.2 (0.3), 1.5 (0.4) and 1.6 (0.5) L/min, respectively (p < 0.001); V'O2 at RCP was 1.7 (0.4), 2.3 (0.8) and 2.6 (0.9) L/min, respectively (p = 0.001). High correlations for VAT and RCP were found between the RATT vs the cycle ergometer and RATT vs the treadmill (R on the range 0.69-0.80). VAT and RCP demonstrated excellent test-retest reliability for all three devices (ICC from 0.81 to 0.98). Mean differences between the test and retest values on each device were close to zero. The ventilatory equivalent for O2 at VAT for the RATT and cycle ergometer were similar and both were higher than the treadmill. The ventilatory equivalent for CO2 at RCP was similar for all devices. Ventilatory equivalent parameters demonstrated fair-to-excellent reliability and repeatability. CONCLUSIONS: It is feasible to use the RATT for estimation of submaximal exercise thresholds: VAT and RCP on the RATT were lower than the cycle ergometer and the treadmill, but there were high correlations between the RATT vs the cycle ergometer and vs the treadmill. Repeatability and test-retest reliability of all submaximal threshold parameters from the RATT were comparable to those of standard devices.

Efficacy of Feedback-Controlled Robotics-Assisted Treadmill Exercise to Improve Cardiovascular Fitness Early After Stroke: A Randomized Controlled Pilot Trial.

BACKGROUND AND PURPOSE: Cardiovascular fitness is greatly reduced after stroke. Although individuals with mild to moderate impairments benefit from conventional cardiovascular exercise interventions, there is a lack of effective approaches for persons with severely impaired physical function. This randomized controlled pilot trial investigated efficacy and feasibility of feedback-controlled robotics-assisted treadmill exercise (FC-RATE) for cardiovascular rehabilitation in persons with severe impairments early after stroke. METHODS: Twenty individuals (age 61 ± 11 years; 52 ± 31 days poststroke) with severe motor limitations (Functional Ambulation Classification 0-2) were recruited for FC-RATE or conventional robotics-assisted treadmill exercise (RATE) (4 weeks, 3 × 30-minute sessions/wk). Outcome measures focused on peak cardiopulmonary performance parameters, training intensity, and feasibility, with examiners blinded to allocation. RESULTS: All 14 allocated participants (70% of recruited) completed the intervention (7/group, withdrawals unrelated to intervention), without serious adverse events occurring. Cardiovascular fitness increased significantly in both groups, with peak oxygen uptake increasing from 14.6 to 17.7 mL · kg · min (+17.8%) after 4 weeks (45.8%-55.7% of predicted maximal aerobic capacity; time effect P = 0.01; no group-time interaction). Training intensity (% heart rate reserve) was significantly higher for FC-RATE (40% ± 3%) than for conventional RATE (14% ± 2%) (P = 0.001). DISCUSSION AND CONCLUSIONS: Substantive overall increases in the main cardiopulmonary performance parameters were observed, but there were no significant between-group differences when comparing FC-RATE and conventional RATE. Feedback-controlled robotics-assisted treadmill exercise significantly increased exercise intensity, but recommended intensity levels for cardiovascular training were not consistently achieved. Future research should focus on appropriate algorithms within advanced robotic systems to promote optimal cardiovascular stress.Video abstract available for more insights from the authors (Supplemental Digital Content 1, http://links.lww.com/JNPT/A107).

Feasibility of cardiopulmonary exercise testing and training using a robotics-assisted tilt table in dependent-ambulatory stroke patients.

BACKGROUND: We evaluated the feasibility of an augmented robotics-assisted tilt table (RATT) for incremental cardiopulmonary exercise testing (CPET) and exercise training in dependent-ambulatory stroke patients. METHODS: Stroke patients (Functional Ambulation Category ≤ 3) underwent familiarization, an incremental exercise test (IET) and a constant load test (CLT) on separate days. A RATT equipped with force sensors in the thigh cuffs, a work rate estimation algorithm and real-time visual feedback to guide the exercise work rate was used. Feasibility assessment considered technical feasibility, patient tolerability, and cardiopulmonary responsiveness. RESULTS: Eight patients (4 female) aged 58.3 ± 9.2 years (mean ± SD) were recruited and all completed the study. For IETs, peak oxygen uptake (V'O2peak), peak heart rate (HRpeak) and peak work rate (WRpeak) were 11.9 ± 4.0 ml/kg/min (45 % of predicted V'O2max), 117 ± 32 beats/min (72 % of predicted HRmax) and 22.5 ± 13.0 W, respectively. Peak ratings of perceived exertion (RPE) were on the range "hard" to "very hard". All 8 patients reached their limit of functional capacity in terms of either their cardiopulmonary or neuromuscular performance. A ventilatory threshold (VT) was identified in 7 patients and a respiratory compensation point (RCP) in 6 patients: mean V'O2 at VT and RCP was 8.9 and 10.7 ml/kg/min, respectively, which represent 75 % (VT) and 85 % (RCP) of mean V'O2peak. Incremental CPET provided sufficient information to satisfy the responsiveness criteria and identification of key outcomes in all 8 patients. For CLTs, mean steady-state V'O2 was 6.9 ml/kg/min (49 % of V'O2 reserve), mean HR was 90 beats/min (56 % of HRmax), RPEs were > 2, and all patients maintained the active work rate for 10 min: these values meet recommended intensity levels for bouts of training. CONCLUSIONS: The augmented RATT is deemed feasible for incremental cardiopulmonary exercise testing and exercise training in dependent-ambulatory stroke patients: the approach was found to be technically implementable, acceptable to the patients, and it showed substantial cardiopulmonary responsiveness. This work has clinical implications for patients with severe disability who otherwise are not able to be tested.

Viscoelastic properties of common suture material used for rotator cuff repair and arthroscopic procedures.

PURPOSE: The purpose of this study was to evaluate the viscoelastic properties of 5 suture materials, commonly used in arthroscopic rotator cuff repairs, when subjected to physiological loads. METHODS: We evaluated 5 commercially available No. 2 sutures undergoing both creep and cyclic testing in both dry air and phosphate-buffered saline solution (PBS) maintained at 37°C. The selected sutures were MagnumWire (ArthroCare, Austin, TX), Ethibond (Ethicon, Somerville, NJ), FiberWire (Arthrex, Naples, FL), Orthocord (DePuy, Warsaw, IN), and Force Fiber (Tornier, Bloomington, MN). RESULTS: Regarding creep testing, in the PBS test environment, FiberWire showed the greatest stiffness (71.1 ± 2.1 N/mm), the smallest initial extension at the 60-N load (1.10 ± 0.04 mm), and the smallest amount of creep (0.57 ± 0.01 mm). Orthocord showed the smallest amount of relaxed elongation in PBS (0.73 ± 0.11 mm). Regarding cyclic testing, in the PBS testing environment, Ethibond exhibited the smallest dynamic creep (0.28 ± 0.02 mm), FiberWire displayed the smallest peak-to-peak displacement (0.17 ± 0.00 mm), and Orthocord showed the smallest amount of relaxed elongation after cyclic loading (0.63 ± 0.11 mm). CONCLUSIONS: FiberWire consistently displayed more extreme viscoelastic properties--greater stiffness and less extensibility--than the other suture types studied. Orthocord showed the smallest amount of relaxed elongation in both testing environments. Differences in testing environment affect the behavior of each suture type. Testing in physiologically approximating conditions such as PBS maintained at 37°C is warranted. CLINICAL RELEVANCE: Although many other factors affect the success of rotator cuff repairs, the viscoelastic properties of sutures may be a useful predictor of suture performance.

Mechanical stimulation of the foot sole in a supine position for ground reaction force simulation.

BACKGROUND: To promote early rehabilitation of walking, gait training can start even when patients are on bed rest. Supine stepping in the early phase after injury is proposed to maximise the beneficial effects of gait restoration. In this training paradigm, mechanical loading on the sole of the foot is required to mimic the ground reaction forces that occur during overground walking. A pneumatic shoe platform was developed to produce adjustable forces on the heel and the forefoot with an adaptable timing. This study aimed to investigate the stimulation parameters of the shoe platform to generate walking-like loading on the foot sole, while avoiding strong reflexes. METHODS: This study evaluated this platform in ten able-bodied subjects in a supine position. The platform firstly produced single-pulse stimulation on the heel or on the forefoot to determine suitable stimulation parameters, then it produced cyclic stimulation on the heel and the forefoot to simulate the ground reaction forces that occur at different walking speeds. The ankle angle and electromyography (EMG) in the tibialis anterior (TA) and soleus (SOL) muscles were recorded. User feedback was collected. RESULTS: When the forefoot or/and the heel were stimulated, reflexes were observed in the lower leg muscles, and the amplitude increased with force. Single-pulse stimulation showed that a fast-rising force significantly increased the reflex amplitudes, with the possibility of inducing ankle perturbation. Therefore a slow-rising force pattern was adopted during cyclic stimulation for walking. The supine subjects perceived loading sensation on the foot sole which was felt to be similar to the ground reaction forces during upright walking. The EMG generally increased with force amplitude, but no reflex-induced ankle perturbations were observed. The mean change in the ankle joint induced by the stimulation was about 1°. CONCLUSIONS: The rate of force increase should be carefully adjusted for simulation of walking-like loading on the foot sole. It is concluded that the dynamic shoe platform provides adjustable mechanical stimulation on the heel and the forefoot in a supine position and has technical potential for simulation of ground reaction forces that occur during walking.

Cardiopulmonary exercise testing early after stroke using feedback-controlled robotics-assisted treadmill exercise: test-retest reliability and repeatability.

BACKGROUND: Exercise capacity is seriously reduced after stroke. While cardiopulmonary assessment and intervention strategies have been validated for the mildly and moderately impaired populations post-stroke, there is a lack of effective concepts for stroke survivors suffering from severe motor limitations. This study investigated the test-retest reliability and repeatability of cardiopulmonary exercise testing (CPET) using feedback-controlled robotics-assisted treadmill exercise (FC-RATE) in severely motor impaired individuals early after stroke. METHODS: 20 subjects (age 44-84 years, <6 month post-stroke) with severe motor limitations (Functional Ambulatory Classification 0-2) were selected for consecutive constant load testing (CLT) and incremental exercise testing (IET) within a powered exoskeleton, synchronised with a treadmill and a body weight support system. A manual human-in-the-loop feedback system was used to guide individual work rate levels. Outcome variables focussed on standard cardiopulmonary performance parameters. Relative and absolute test-retest reliability were assessed by intraclass correlation coefficients (ICC), standard error of the measurement (SEM), and minimal detectable change (MDC). Mean difference, limits of agreement, and coefficient of variation (CoV) were estimated to assess repeatability. RESULTS: Peak performance parameters during IET yielded good to excellent relative reliability: absolute peak oxygen uptake (ICC =0.82), relative peak oxygen uptake (ICC =0.72), peak work rate (ICC =0.91), peak heart rate (ICC =0.80), absolute gas exchange threshold (ICC =0.91), relative gas exchange threshold (ICC =0.88), oxygen cost of work (ICC =0.87), oxygen pulse at peak oxygen uptake (ICC =0.92), ventilation rate versus carbon dioxide output slope (ICC =0.78). For these variables, SEM was 4-13%, MDC 12-36%, and CoV 0.10-0.36. CLT revealed high mean differences and insufficient test-retest reliability for all variables studied. CONCLUSIONS: This study presents first evidence on reliability and repeatability for CPET in severely motor impaired individuals early after stroke using a feedback-controlled robotics-assisted treadmill. The results demonstrate good to excellent test-retest reliability and appropriate repeatability for the most important peak cardiopulmonary performance parameters. These findings have important implications for the design and implementation of cardiovascular exercise interventions in severely impaired populations. Future research needs to develop advanced control strategies to enable the true limit of functional exercise capacity to be reached and to further assess test-retest reliability and repeatability in larger samples.

Clinical Outcomes and Registry Data in Total Ankle Arthroplasty.

Total ankle arthroplasty (TAA) is an effective treatment for end-stage ankle arthritis consistently demonstrating good to excellent outcomes, even when considering factors such as deformity, patient age, bilaterality, and arthritis etiology. There is little consensus in the literature with regard to preferred patient-reported outcome metrics (PROMs) for assessing outcomes, although all metrics generally improve following TAA. Several countries have successful registries to track longevity of TAA in populations; however, PROMs are generally not successfully tracked in registries. A trend toward consensus on outcome metrics and collaborative registries is warranted to optimize patient selection and outcomes in TAA.

Playing Surface and Sport Contact Status Modulate Time to Lower Extremity Musculoskeletal Injury at a Greater Level than Concussion History Among Collegiate Student-Athletes.

OBJECTIVES: While previous investigations have demonstrated a positive correlation between previous concussion and risk of subsequent lower extremity musculoskeletal injury (LEMSKI), the effect of sport- and patient-specific factors on time to injury has not been thoroughly described. This study's main objective was to evaluate the relationship between prior concussion and time to LEMSKI among a population of collegiate student-athletes. Secondary objectives were to evaluate the relationship between playing surface, sport contact status, and biologic sex on time to LEMSKI. We hypothesized that those with previous concussion, those competing on synthetic surfaces, and those competing in collision sports would experience decreased latency to LEMSKI overall. METHODS: A retrospective observational analysis of National Collegiate Athletic Association (NCAA) Division I student-athletes was conducted utilizing a mixed linear model analysis with contrasts. Inclusion criteria included participation in the Pac-12 Health Analytics Program with a documented LEMSKI between 2017 and 2020. Exclusion criteria included concurrent concussion and LEMSKI, injury resulting in serious morbidity or mortality, and incomplete medical record. Participants were classified by whether they sustained a concussion prior to LEMSKI in each athletic season. RESULTS: Of 1179 athletes included, 1140 had no previous concussion and 37 had a previous concussion. There was no observed effect of previous concussion (F=0.038; p=0.846) on time to LEMSKI overall. Student-athletes competing on constructed surfaces sustained a subsequent LEMSKI 14.5 days sooner (SE=5.255; p=0.045), and those competing on organic surfaces sustained a subsequent LEMSKI 23.5 days sooner (SE=4.018; p<0.001) in the season than those competing on synthetic surfaces. Contact sport student-athletes sustained a subsequent LEMSKI 52.1 days sooner than collision sport student-athletes (SE=5.248; p<0.001), and limited contact sport student-athletes sustained a subsequent LEMSKI 42.29 days sooner than collision sport student-athletes (SE=4.463; p<0.001). There was no observed effect of biologic sex (F=0.602; p=0.438) on time to LEMSKI overall. CONCLUSION: There was no observed impact of concussion on time to LEMSKI overall in this collegiate athletic population. Contact sports were associated with decreased time to LEMSK, while synthetic surfaces were associated with increased time to LEMSKI in this population. There was no observed impact of biologic sex on time to LEMSKI. LEVEL OF EVIDENCE: Case-control, level of evidence III.