Quadriceps Oxygenation During Exercise in Patients With Anterior Cruciate Ligament Reconstruction

Overexpression of manganese superoxide dismutase mitigates ACL injury-induced muscle atrophy, weakness and oxidative damage

Oxidative stress has been implicated in the etiology of skeletal muscle weakness following joint injury. We investigated longitudinal patient muscle samples following knee injury (anterior cruciate ligament tear). Following injury, transcriptomic analysis revealed downregulation of mitochondrial metabolism-related gene networks, which were supported by reduced mitochondrial respiratory flux rates. Additionally, enrichment of reactive oxygen species (ROS)-related pathways were upregulated in muscle following knee injury, and further investigation unveiled marked oxidative damage in a progressive manner following injury and surgical reconstruction. We then investigated whether antioxidant protection is effective in preventing muscle atrophy and weakness after knee injury in mice that overexpress Mn-superoxide dismutase (MnSOD+/-). MnSOD+/- mice showed attenuated oxidative damage, atrophy, and muscle weakness compared to wild type littermate controls following ACL transection surgery. Taken together, our results indicate that ROS-related damage is a causative mechanism of muscle dysfunction after knee injury, and that mitochondrial antioxidant protection may hold promise as a therapeutic target to prevent weakness and development of disability.

Monitoring Muscle Oxygen Asymmetry as a Strategy to Prevent Injuries in Footballers

Purpose: It has been hypothesized that sports injury risk is explained by muscle metabolism. The objective was to evaluate the muscle oxygen saturation slopes (ΔSmO2 slopes) and muscle oxygenation asymmetry (MO2Asy) at rest and to study their associations with injuries during the pre-season. Methods: A total of 16 male and 10 female footballers participated in this study. Injuries were diagnosed and classified by level of severity during the pre-season. The workload was also evaluated using the rate of perceived exertion × training time, from which the accumulated loads. The SmO2 was measured at rest in the gastrocnemius muscle using the arterial occlusion method in the dominant and non-dominant legs. The repeated measures ANOVA, relative risk, and binary logistic regression were applied to assess the probability of injury with SmO2 and workload. Results: Higher MO2Asy and ΔSmO2 Slope 2 were found among footballer who suffered high-severity injuries and those who presented no injuries. In addition, an MO2Asy greater than 15% and an increase in accumulated load were variables that explained a greater probability of injury. Conclusion: This study presents the new concept of muscle oxygenation asymmetry in sports science and its possible application in injury prevention through the measurement of SmO2 at rest.

Treatment side affects exercising microvascular oxygenation response in active breast cancer survivors: A pilot study

Cancer treatment is associated with cardiovascular toxicity, skeletal muscle dysfunction and interruptions in mitochondrial respiration. Microvascular oxygenation responses, measured via near-infrared spectroscopy (NIRS), at peak exercise intensity has previously been associated with aerobic capacity. Specifically, the greater magnitude of microvascular deoxygenation observed at peak exercise intensity has been associated with higher aerobic capacity. Therefore, a pilot study investigated if diagnosis side (uninvolved side, treatment side) and/or exercise side (paddle side, non-paddle side) affected microvascular oxygenation responses at peak intensity during paddle exercise. Thirty-three breast cancer survivors (age = 57 ± 9 years, height = 1.64 ± 0.05 m, weight = 76.5 ± 15.6 kg, 7 ± 7 years since treatment) who also competed as dragon boat racers performed a unilateral (paddle), discontinuous graded exercise test (2-min exercise, 1-min rest) on a rowing ergometer to volitional fatigue. Tissue oxygenation saturation (StO_2DIFF ) and total haemoglobin concentration (total[heme]_DIFF ) responses at peak exercise intensity were measured bilaterally from the posterior deltoids using NIRS. Two-way analysis of variance determined if diagnosis side and/or exercise side effected StO_2DIFF or total[heme]_DIFF . Diagnosis side elicited a moderate effect (effect size = 0.66) on StO_2DIFF , as the treatment side deoxygenated less (-6.0 ± 14.7 ∆BSL) compared to the uninvolved side (-16.9 ± 16.9 ∆BSL) at peak exercise intensity. No other significant main effects or interactions were observed for StO_2DIFF or total[heme]_DIFF . The pilot findings suggest that the ability of the exercising muscle to use oxygen for the purpose of mitochondrial oxidative respiration may be impaired on the treatment side.

Acute Effects of 3 Neuromuscular Electrical Stimulation Waveforms on Exercising and Recovery Microvascular Oxygenation Responses

CONTEXT

When emphasizing muscular strength during postoperative rehabilitation it is recommended to use a neuromuscular electrical stimulation (NMES) waveform that elicits the greatest muscle force and local metabolic demand that is also well tolerated. The present investigation examined the effects that 3 different clinically used NMES waveforms had on the electrically elicited force (EEF), local metabolic demand (exercising muscle oxygen saturation [SmO2]), and the subsequent reactive hyperemia response (recovery total hemoglobin concentration [THb]) of the knee extensors.

DESIGN

Single session repeated-measures design.

METHODS

EEF, local metabolic demand, and reactive hyperemia responses were measured during and subsequent to 3 NMES waveforms: Russian burst modulated alternating current (RUS), biphasic pulsed current (VMS™), and burst modulated biphasic pulsed current (VMS-Burst™). Exercising SmO2 and recovery THb were assessed noninvasively using a near-infrared spectroscopy sensor placed on the vastus lateralis. Participants completed one set of 10 repetitions of each NMES waveform and were provided with 5 minutes of passive, interset recovery. Two-way, repeated-measures analysis of variance examined if NMES waveform or repetition significantly affected (P < .05) EEF or exercising SmO2. Two-way, repeated-measures analysis of variance examined if NMES waveform or recovery time affected recovery THb.

RESULTS

VMS™ and VMS-Burst™ yielded higher EEF (F = 11.839, P < .001) and greater local metabolic stress (lower exercising SmO2, F = 13.654, P < .001) compared with RUS. Greater rate of EEF decline throughout the NMES set was observed during RUS (%Δ = -50 [6] %Rep1) compared with VMS-Burst™ (%Δ = -30 [7] %Rep1) and VMS™ (%Δ = -32 [7] %Rep1). VMS™ elicited a higher reactive hyperemia response (higher recovery THb) compared with RUS (F = 3.427, P = .048).

CONCLUSIONS

The present findings support the use of VMS™ or VMS-Burst™ compared with RUS when promoting muscular strength. In addition, the use of VMS™ might provide a greater blood volume to the target muscle subsequent to NMES contractions compared with RUS.

Long-Lasting Impairments in Quadriceps Mitochondrial Health, Muscle Size, and Phenotypic Composition Are Present After Non-invasive Anterior Cruciate Ligament Injury

Introduction

Despite rigorous rehabilitation aimed at restoring muscle health, anterior cruciate ligament (ACL) injury is often hallmarked by significant long-term quadriceps muscle weakness. Derangements in mitochondrial function are a common feature of various atrophying conditions, yet it is unclear to what extent mitochondria are involved in the detrimental sequela of quadriceps dysfunction after ACL injury. Using a preclinical, non-invasive ACL injury rodent model, our objective was to explore the direct effect of an isolated ACL injury on mitochondrial function, muscle atrophy, and muscle phenotypic transitions.

Methods

A total of 40 male and female, Long Evans rats (16-week-old) were exposed to non-invasive ACL injury, while 8 additional rats served as controls. Rats were euthanized at 3, 7, 14, 28, and 56 days after ACL injury, and vastus lateralis muscles were extracted to measure the mitochondrial respiratory control ratio (RCR; state 3 respiration/state 4 respiration), mitochondrial reactive oxygen species (ROS) production, fiber cross sectional area (CSA), and fiber phenotyping. Alterations in mitochondrial function and ROS production were detected using two-way (sex:group) analyses of variance. To determine if mitochondrial characteristics were related to fiber atrophy, individual linear mixed effect models were run by sex.

Results

Mitochondria-derived ROS increased from days 7 to 56 after ACL injury (30–100%, P &lt; 0.05), concomitant with a twofold reduction in RCR (P &lt; 0.05). Post-injury, male rats displayed decreases in fiber CSA (days 7, 14, 56; P &lt; 0.05), loss of IIa fibers (day 7; P &lt; 0.05), and an increase in IIb fibers (day 7; P &lt; 0.05), while females displayed no changes in CSA or phenotyping (P &gt; 0.05). Males displayed a positive relationship between state 3 respiration and CSA at days 14 and 56 (P &lt; 0.05), while females only displayed a similar trend at day 14 (P = 0.05).

Conclusion

Long-lasting impairments in quadriceps mitochondrial health are present after ACL injury and play a key role in the dysregulation of quadriceps muscle size and composition. Our preclinical data indicate that using mitoprotective therapies may be a potential therapeutic strategy to mitigate alterations in muscle size and characteristic after ACL injury.