Changes in muscle oxygenation during weight-lifting exercise

Similar Slow Component of Oxygen Uptake and Ventilatory Efficiency between an Aerobic Dance Session on an Air Dissipation Platform and a Constant-Load Treadmill Test in Healthy Women

There is a lack of evidence about the slow component of oxygen consumption (V.O2sc) and ventilatory efficiency (slope VE·VCO2−1) during an aerobic dance (AD) session on an air dissipation platform (ADP) despite the key role played in endurance exercises. This research was designed to assess V.O2sc, ventilatory efficiency, and blood lactate concentration by comparing two exercise modes: AD session on an ADP versus treadmill test at a constant-load intensity of the first ventilatory threshold (VT1). In the first session, an incremental treadmill test was completed. In sessions 2 and 3, the participants were randomly assigned to the AD session on an ADP or to a treadmill constant-load test at VT1 intensity to determine their cardioventilatory responses. In addition, their blood lactate levels and ratings of perceived exertion (RPE, CR-10) were evaluated. No significant differences were found between the constant-load treadmill test and AD session on an ADP with respect to V.O2sc, VE VCO2−1 slope, and RPE (p > 0.05). Higher blood lactate concentrations were observed in an AD session on an ADP than in a constant-load treadmill test at 10 min (p = 0.003) and 20 min (p < 0.001). The two different exercise modalities showed similar V.O2sc and VE·VCO2−1 slope, even though the blood lactate concentrations were different.

Vector-based analysis of cortical activity associated with dumbbell exercise using functional near-infrared spectroscopy

The mechanisms via which the brain and muscles work together remain poorly understood. The use of vector-based fNIRS, to propose a new metric and imaging method to understand neural activation during dumbbell-lifting exercises. This method can simultaneously measure oxyhemoglobin (oxyHb) and deoxyHb levels so that the angle k: Arctan (deoxyHb/oxyHb) represents the degree of oxygen exchange in the brain and can be used to quantify the distribution of oxygen consumption. The amplitude L of the vector reflects the intensity of the response caused by the amount of change in Hb. This study used vector-based fNIRS to simultaneously measure the left primary motor cortex (left M1), multiple peripheral regions, and the right biceps brachii muscle. The subjects were seven healthy adults. The task was a dumbbell-lifting exercise involving flexion and extension of the elbow joints of both arms. Dumbbell weights of 0 (no dumbbell), 4.5, and 9.5 kg were used. During dumbbell exercise, oxygen exchange increased in the left M1, indicating increased local oxygen consumption. Around the left M1, the cerebral oxygen exchange decreased, and oxygen supply increased without cerebral oxygen consumption. The spatial agreement between the maximum value of oxygen exchange k and L during the task was <20%. Therefore, the dumbbell-lifting exercise task study reported here supported the hypothesis that cerebral oxygen consumption associated with neural activation does not coincide with the distribution of cerebral oxygen supply. The relationship between the brain oxygen supply from the site of increased oxygen exchange in the brain and its surrounding areas can be quantified using the vector method fNIRS.

Are mode-specific differences in performance fatigability attributable to muscle oxygenation?

PURPOSE

The purpose of this study was to examine the composite, intra-individual, and inter-individual patterns of responses for deoxygenated hemoglobin and myoglobin (deoxy[heme]), oxygenated hemoglobin and myoglobin (oxy[heme]), total hemoglobin and myoglobin (total[heme]), and tissue saturation index (StO₂%) during fatiguing, maximal, isokinetic, unilateral, and bilateral leg extensions.

METHODS

Nine men (Mean ± SD; age = 21.9 ± 2.4 years; height = 181.8 ± 11.9 cm; body mass = 85.8 ± 6.2 kg) performed 50 unilateral and bilateral maximal, concentric, isokinetic leg extensions at 180° s^-1 on two separate visits. The muscle oxygenation parameters assessed with near-infrared spectroscopy from the dominant leg and isokinetic torque were averaged for 2 consecutive repetitions at 5 repetition intervals. Separate 2 (Condition [Unilateral and Bilateral]) × 10 (Repetition [5-50]) repeated measures ANOVAs were performed to examine mean differences for normalized isokinetic torque and each muscle oxygenation parameter. Intra- and inter-individual differences were examined with polynomial regression analyses.

RESULTS

For normalized isokinetic torque, the unilateral condition (56.3 ± 10.5%) exhibited greater performance fatigability than the bilateral condition (45.0 ± 18.7%). Collapsed across Condition, deoxy[heme] exhibited an increase (p < 0.001), while StO₂% exhibited a decrease (p < 0.001). The bilateral condition exhibited a more sustained decline in oxy[heme] than the unilateral condition (p = 0.005). Deoxy[heme], oxy[heme], and total[heme] exhibited substantial intra- and inter-individual differences for the fatigue-induced patterns of response.

CONCLUSION

The present findings indicated that the greater performance fatigability for unilateral versus bilateral fatiguing, maximal, isokinetic leg extensions was not attributable to differences in muscle oxygenation. Future studies of muscle oxygenation should report individual and composite fatigue-induced patterns of responses due to the substantial intra- and inter-individual variabilities.

Lower-limb Dynamics of Muscle Oxygen Saturation During the Back-squat Exercise: Effects of Training Load and Effort Level

Gómez-Carmona, CD, Bastida-Castillo, A, Rojas-Valverde, D, de la Cruz Sánchez, E, García-Rubio, J, Ibáñez, SJ, and Pino-Ortega, J. Lower-limb dynamics of muscle oxygen saturation during the back-squat exercise: effects of training load and effort level. J Strength Cond Res 34(5): 1227-1236, 2020-The aim of this study was to analyze the effect of strength training on lower limb muscle oxygenation. The sample consisted of 12 male subjects (22.4 ± 1.73 years; 1.81 ± 0.08 cm height and 77.76 ± 8.77 kg body mass). Six different strength training stimuli were analyzed, based on the training variables: load (60-75% 1 repetition maximum [1RM]) and level of effort (LE) (E1: 4 × 8 [20RM], E2: 4 × 12 [20RM], E3: 4 × 16 [20RM], E4: 4 × 4 [10RM], E5: 4 × 6 [10RM], and E6: 4 × 8 [10RM]) in the squat exercise up to 90° with a 2-second stop between repetitions to avoid the myotatic reflex. Oxygen saturation at the beginning of the series (SmO2start), oxygen saturation at the end of the series (SmO2stop), percentage of oxygen saturation loss (▽%SmO2), and reoxygenation time (SmO2recT) were assessed using a near-infrared spectroscopy device. In addition, the percentage of mean propulsive velocity loss (%MPVL) was recorded using a linear transducer. The results suggested an influence of LE and training load on muscle oxygenation. A greater LE was directly associated with SmO2recT (r = 0.864), ▽%SmO2 (r = 0.873), and %MPVL (r = 0.883) and inversely with SmO2stop (r = -0.871). When the same LE was used (E1 vs. E4, E2 vs. E5, and E3 vs. E6), it was found that the stimuli with a higher load had a lower SmO2recT, ▽%SmO2, and %MPVL and a higher SmO2stop. Muscle oxygen saturation was found to be minimal (%SmO2 = 0) in stimuli with a LE greater than 60% (E3 and E6). The SmO2 variables studied in the present research could be considered as an easier and more useful method for understanding skeletal muscle fatigue during resistance training.

Effects of knee extension with different speeds of movement on muscle and cerebral oxygenation

Background

One of the mechanisms responsible for enhancing muscular hypertrophy is the high metabolic stress associated with a reduced muscular oxygenation occurring during exercise, which can be achieved by reducing the speed of movement. Studies have tested that lowered muscle oxygenation artificially induced by an inflatable cuff, could provoke changes in prefrontal cortex oxygenation, hence, to central fatigue. It was hypothesized that (1) exercising with a slow speed of movement would result in greater increase in cerebral and greater decrease in muscle oxygenation compared with exercises of faster speed and (2) the amount of oxygenation increase in the ipsilateral prefrontal cortex would be lower than the contralateral one.

Methods

An ISS Imagent frequency domain near infrared spectroscopy (NIRS) system was used to quantify oxygenation changes in the vastus lateralis muscle and prefrontal cortex (contra- and ipsilateral) during unilateral resistance exercises with different speeds of movement to voluntary fatigue. After one maximal repetition (1RM) test, eight subjects performed three sets of unilateral knee extensions (∼50% of 1RM), separated by 2 min rest periods, following the pace of 1 s, 3 s and 5 s for both concentric and eccentric phases, in a random order, during separate sessions. The amount of change for NIRS parameters for muscle (ΔHb: deoxyhemoglobin, ΔHbO: oxyhemoglobin, ΔHbT: total hemoglobin, ΔStO₂: oxygen saturation) were quantified and compared between conditions and sets by two-way ANOVA RM. Differences in NIRS parameters between contra- and ipsilateral (lobe) prefrontal cortex and conditions were tested.

Results

Exercising with slow speed of movement was associated to larger muscle deoxygenation than normal speed of movement, as revealed by significant interaction (set × condition) for ΔHb (p = 0.01), and by significant main effects of condition for ΔHbO (p = 0.007) and ΔStO₂ (p = 0.016). With regards to the prefrontal cortex, contralateral lobe showed larger oxygenation increase than the ipsilateral one for ΔHb, ΔHbO, ΔHbT, ΔStO₂ in each set (main effect of lobe: p < 0.05). Main effects of condition were significant only in set1 for all the parameters, and significant interaction lobe × condition was found only for ΔHb in set1 (p < 0.05).

Discussion

These findings provided evidence that speed of movement influences the amount of muscle oxygenation. Since the lack of oxygen in muscle is associated to increased metabolic stress, manipulating the speed of movement may be useful in planning resistance-training programs. Moreover, consistent oxygenation increases in both right and left prefrontal lobes were found, suggesting a complementary interaction between the ipsi- and contralateral prefrontal cortex, which also seems related to fatigue.

Neuromuscular Activity and Muscular Oxygenation Through Different Movement Cadences During In-water and On-land Knee Extension Exercise

Chien, K-Y, Kan, N-W, Liao, Y-H, Lin, Y-L, Lin, C-L, and Chen, W-C. Neuromuscular activity and muscular oxygenation through different movement cadences during in-water and on-land knee extension exercise. J Strength Cond Res 31(3): 750-757, 2017-The purpose of this study was to determine the influence of various knee extension exercise cadences on neuromuscular activation and hemodynamic properties of the quadriceps muscle in water and on land. Seventeen young women participated in this study, and the subjects were randomly allocated to perform loaded knee extension exercises in water and on land at 4 different cadences of 30, 50, 70, and 90 b·min. Heart rate (HR), blood flow (BF), total saturation index (TSI) of oxygen, electromyography (EMG) for the extent of muscular activity, and rate of perceived exertion (RPE) were measured. Response values of HR, BF, TSI, and RPE at each cadence were obtained by subtracting the resting values from the indicator values measured at the respective cadences. We observed that BF, EMG, and RPE in water at 90 b·min were comparable with those on land. The HR and TSI changes were higher in water compared with on land (p = 0.004 and p = 0.013, respectively). In conclusion, we demonstrate that the neuromuscular activity when performing knee extension exercises at 90 b·min in water was comparable with that on land. However, exercising in water at the same cadence evoked higher TSI responses and greater cardiovascular challenges. A knee extension exercise at 90 b·min is the recommended operating speed of rehabilitation in water.

Hypoxia and resistance exercise: a comparison of localized and systemic methods

It is generally believed that optimal hypertrophic and strength gains are induced through moderate- or high-intensity resistance training, equivalent to at least 60% of an individual's 1-repetition maximum (1RM). However, recent evidence suggests that similar adaptations are facilitated when low-intensity resistance exercise (~20-50% 1RM) is combined with blood flow restriction (BFR) to the working muscles. Although the mechanisms underpinning these responses are not yet firmly established, it appears that localized hypoxia created by BFR may provide an anabolic stimulus by enhancing the metabolic and endocrine response, and increase cellular swelling and signalling function following resistance exercise. Moreover, BFR has also been demonstrated to increase type II muscle fibre recruitment during exercise. However, inappropriate implementation of BFR can result in detrimental effects, including petechial haemorrhage and dizziness. Furthermore, as BFR is limited to the limbs, the muscles of the trunk are unable to be trained under localized hypoxia. More recently, the use of systemic hypoxia via hypoxic chambers and devices has been investigated as a novel way to stimulate similar physiological responses to resistance training as BFR techniques. While little evidence is available, reports indicate that beneficial adaptations, similar to those induced by BFR, are possible using these methods. The use of systemic hypoxia allows large groups to train concurrently within a hypoxic chamber using multi-joint exercises. However, further scientific research is required to fully understand the mechanisms that cause augmented muscular changes during resistance exercise with a localized or systemic hypoxic stimulus.

An examination of the differences between two methods of estimating energy expenditure in resistance training activities

To date, few studies have looked at the energy expenditure (EE) of individual resistance training (RT) exercises. The purpose of this study was to evaluate the EE of 4 modes of RT (push-ups, curl-ups, pull-ups, and lunges) using 2 different calculation methods for estimating EE. Twelve healthy men with a minimum of 1 year of RT experience were randomly assigned to an RT circuit. Each circuit contained the 4 RT exercises in a specified order. The participants completed 3 trials of their assigned circuit during one visit to the laboratory. Oxygen consumption was measured continuously throughout the trial using indirect calorimetry. Two different calculation methods were applied to estimate EE. Using the traditional method (TEC), we estimated EE by calculating the average oxygen consumption recorded during each activity. Using the second, nontraditional method (NEC), we estimated EE by calculating the average oxygen consumption recorded during the recovery period. Independent T-tests were used to evaluate mean EE differences between the 2 methods. Estimates of EE obtained from the NEC were significantly higher for all the 4 activities (p < 0.001). Using the NEC, 3 of the 4 activities were classified as vigorous intensity (push-ups: 6.91 metabolic equivalents (METs); lunges: 7.52 METs; and pull-ups: 8.03 METs), whereas none were classified as vigorous using the TEC. Findings suggest that the methods we use to calculate the EE of anaerobic activities significantly affect EE estimates. Using the TEC may underestimate actual EE of anaerobic activities.

Investigating the adaptation of muscle oxygenation to resistance training for elders and young men using near-infrared spectroscopy

PURPOSE

The purpose of this study was to investigate the differences in resistance training adaptation on muscle oxygenation between young and elderly subjects. Groups of eleven trained young, untrained young, trained elderly, and untrained elderly (UTE) were recruited.

METHODS

Muscle oxygenation of the vastus lateralis muscle during 20 % maximal voluntary isometric contraction was observed using near-infrared spectroscopy. The oxygen saturation (SpO2) kinetics in the contraction and recovery phases was modeled with a tangential model to extract ΔSpO2 and inflection time (IF). The median frequencies of SpO2 data representing the change of tissue oxygenation oscillation were compared.

RESULTS

The ΔSpO2 values for the trained groups (12.00 ± 7.86%) were significantly higher than those for the untrained groups (5.91 ± 4.36%, P < 0.05), and those for the young groups (11.63 ± 7.52%) were significantly higher than those for the older groups (6.29 ± 4.70%, P < 0.05). In the recovery phase, the IF was significantly longer for the elderly groups (10.32 ± 4.39 s, P < 0.05) than that for the young groups (6.31 ± 3.69 s). The median frequency of tissue oxygenation oscillation was significantly lower for the TE group (0.41 ± 0.12 Hz, P < 0.05) than that for the UTE group (0.57 ± 0.13 Hz).

CONCLUSIONS

The increased ΔSpO2 in trained groups during muscle contraction may be due to lower microvascular O2 pressure. The lower median frequency for the TE group indicates that tissue oxygenation oscillation significantly trended toward low-frequency oscillation, possibly resulting from the enhancement of vascular function.

Estimating the energy costs of intermittent exercise

To date, steady state models represent the only acceptable methodology for the estimation of exercise energy costs. Conversely, comparisons made between continuous and intermittent exercise generally reveal major physiological discrepancies, leading to speculation as to why steady state energy expenditure models should be applied to intermittent exercise. Under intermittent conditions, skeletal muscle invokes varying aerobic and anaerobic metabolic responses, each with the potential to make significant contributions to overall energy costs. We hypothesize that if the aerobic-only energetic profile of steady state exercise can be used to estimate the energetics of non-steady state and intermittent exercise, then the converse also must be true. In fact, reasonable estimates of energy costs to work volumes or work rates can be demonstrated under steady state, non-steady state and intermittent conditions; the problem with the latter two is metabolic variability. Using resistance training as a model, estimates of both aerobic and anaerobic energy cost components, as opposed to one or the other, have reduced the overall energetic variability that appears inherent to brief, intense, intermittent exercise models.

Potential mechanisms for a role of metabolic stress in hypertrophic adaptations to resistance training

It is well established that regimented resistance training can promote increases in muscle hypertrophy. The prevailing body of research indicates that mechanical stress is the primary impetus for this adaptive response and studies show that mechanical stress alone can initiate anabolic signalling. Given the dominant role of mechanical stress in muscle growth, the question arises as to whether other factors may enhance the post-exercise hypertrophic response. Several researchers have proposed that exercise-induced metabolic stress may in fact confer such an anabolic effect and some have even suggested that metabolite accumulation may be more important than high force development in optimizing muscle growth. Metabolic stress pursuant to traditional resistance training manifests as a result of exercise that relies on anaerobic glycolysis for adenosine triphosphate production. This, in turn, causes the subsequent accumulation of metabolites, particularly lactate and H(+). Acute muscle hypoxia associated with such training methods may further heighten metabolic buildup. Therefore, the purpose of this paper will be to review the emerging body of research suggesting a role for exercise-induced metabolic stress in maximizing muscle development and present insights as to the potential mechanisms by which these hypertrophic adaptations may occur. These mechanisms include increased fibre recruitment, elevated systemic hormonal production, alterations in local myokines, heightened production of reactive oxygen species and cell swelling. Recommendations are provided for potential areas of future research on the subject.

Cell-free plasma DNA and purine nucleotide degradation markers following weightlifting exercise

The present study aimed to investigate the acute effects of a single bout of high-intensive strength training on the production of cell-free plasma DNA (cf-DNA), as well as on the degradation of purine nucleotides as assessed by the concentration of xanthine (XA) and hypoxanthine (HX) in urine and serum. Twelve trained weightlifters performed six sets of six lifting exercises with 90-95% of the one repetition maximum. Blood samples and urine were obtained 1 h before training, immediately after finishing the exercise session and following 2 h of recovery. Cf-DNA, HX, and XA (in serum) significantly increased (P < 0.05-P < 0.001) immediately after heavy lifting exercise when compared with baseline levels, and significantly decreased (P < 0.05-P < 0.001) after 2 h of recovery. These results indicate that, cf-DNA and oxypurines might be relevant biomarkers for cellular damage, mechanical, energetic, and/or ischemic stress in context with exercise.

Near-infrared spectroscopy/imaging for monitoring muscle oxygenation and oxidative metabolism in healthy and diseased humans

Near-infrared spectroscopy (NIRS) was initiated in 1977 by Jobsis as a simple, noninvasive method for measuring the presence of oxygen in muscle and other tissues in vivo. This review honoring Jobsis highlights the progress that has been made in developing and adapting NIRS and NIR imaging (NIRI) technologies for evaluating skeletal muscle O(2) dynamics and oxidative energy metabolism. Development of NIRS/NIRI technologies has included novel approaches to quantification of the signal, as well as the addition of multiple source detector pairs for imaging. Adaptation of NIRS technology has focused on the validity and reliability of NIRS measurements. NIRS measurements have been extended to resting, ischemic, localized exercise, and whole body exercise conditions. In addition, NIRS technology has been applied to the study of a number of chronic health conditions, including patients with chronic heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, varying muscle diseases, spinal cord injury, and renal failure. As NIRS technology continues to evolve, the study of skeletal muscle function with NIRS first illuminated by Jobsis continues to be bright.

A brief review of the use of near infrared spectroscopy with particular interest in resistance exercise

There is growing interest in resistance training, but many aspects related to this type of exercise are still not fully understood. Performance varies substantially depending on how resistance training variables are manipulated. Fatigue is a complex phenomenon usually attributed to central (neuronal) and/or peripheral (muscular) origin. Cerebral oxygenation may be associated with the decision to stop exercise, and muscle oxygenation may be related to resistance training responses. Near infrared spectroscopy (NIRS) is a non-invasive optical technique used to monitor cerebral and muscle oxygenation levels. The purpose of this review is to briefly describe the NIRS technique, validation and reliability, and its application in resistance exercise. NIRS-measured oxygenation in cerebral tissue has been validated against magnetic resonance imaging during motor tasks. In muscle tissue, NIRS-measured oxygenation was shown to be highly related to venous oxygen saturation and muscle oxidative rate was closely related to phosphocreatine resynthesis, measured by (31)P-magnetic resonance spectroscopy after exercise. The test-retest reliability of cerebral and muscle NIRS measurements have been established under a variety of experimental conditions, including static and dynamic exercise. Although NIRS has been used extensively to evaluate muscle oxygenation levels during aerobic exercise, only four studies have used this technique to examine these changes during typical resistance training exercises. Muscle oxygenation was influenced by different resistance exercise protocols depending on the load or duration of exercise, the number of sets and the muscle being monitored. NIRS is a promising, non-invasive technique that can be used to evaluate cerebral and muscle oxygenation levels simultaneously during exercise, thereby improving our understanding of the mechanisms influencing performance and fatigue.

The effects of work experience, lift frequency and exposure duration on low back muscle oxygenation

BACKGROUND

Previous studies have shown changes in low back muscle oxygenation after static muscle contractions or short-term dynamic lifting exertions. The aim of this study was to document the changes in low back muscle oxygenation during prolonged lifting activity over an entire workday as of function of work experience and lift frequency.

METHODS

Four novice and six experienced subjects participated in a lifting study in which they lifted load with a given weight at one of five different frequencies (2, 4, 8, 10, 12 lifts/min) for an 8-h period. Oxygen saturation of the left and right erector spinae was measured continuously and non-invasively using near-infrared spectroscopy during each lifting session.

FINDINGS

Exposure duration had a statistically significant effect on muscle oxygenation level (P<0.0001). Oxygen saturation in the erector spinae increased during the 8-h lifting period. As lift frequency increased, back muscle oxygenation in experienced subjects also increased. In general, the increase in muscle oxygenation for experienced subjects was less than that for novice subjects.

INTERPRETATION

This study suggested that the requirement of oxygen for the low back muscle in a typical industrial lifting job increased over time and experienced workers responded differently from the novice subjects. These findings may provide more insight into the physiological changes of the working muscle and the potential risks of developing muscle injury.

The Effect of Training Volume on the Acute Response and Adaptations to Resistance Training

Purpose:

To examine the acute response to 2 resistance-exercise protocols performed to repetition failure, but different in load configuration, and determine whether the acute response was related to strength increases after 8 weeks of training.

Methods:

Eighteen resistance-trained men completed a single session of 2 resistance-exercise protocols. The constant-load protocol (CL) required subjects to complete 3 sets of single-arm preacher curls (elbow flexion) to failure using a load of ~77% 1RM. The reduced-load protocol (RL) was similar, but training load was reduced for the second and third sets. Maximal isometric force (MVIC) and blood lactate were assessed preprotocol and postprotocol to determine the acute response. For the 8-week training phase, subjects (N = 12) were divided into 2 programs, each corresponsing to 1 of the protocols. Strength was measured before and after training.

Results:

MVIC decreased from 106.2 ± 13.8 to 84.3 ± 12.1 N · m and from 109.1 ± 14.7 to 82.5 ± 13 N · m after the CL and RL protocols, respectively. The decrements in MVIC were significant (P < .001), with the decline after RL tending to be greater (P = .051). Postprotocol blood lactate concentrations after CL and RL were 3.4 ± 1.1 and 4.1 ± 1.3 mmol/L, respectively, with greater increases after RL (P = .036). Similar and significant 1RM strength increases were observed after both programs (from 20.7 ± 2.7 to 23.3 ± 3.5 kg after CL and from 22.4 ± 2.9 to 25.5 ± 3.2 kg after RL; P < .001).

Conclusion:

The similar increases in strength suggest that either the greater acute response to RL was not related to the increases in strength or a minimal (threshold) response was achieved during both programs.

Relationship between oxidative stress in muscle tissue and weight-lifting-induced muscle damage

We examined whether oxidative stress-induced muscle damage occurs during weight-lifting exercise using the rat model. Male Wistar rats were subjected to a single exhaustive session of weight-lifting exercise, and dynamics of blood volume and hemoglobin levels in the exercising muscle were monitored by near-infrared spectroscopy. Total muscle damage was evaluated by the efflux of serum creatine kinase (CK) and uptake of [(3)H]thymidine. The production of reactive oxygen species (ROS) in the muscle was estimated by serial changes in total superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT) activities (established indirect markers). Immunohistochemical detection of GPX was also performed. A relatively anoxic state occurred repeatedly after every exercise set in exercising muscle following rapid blood reperfusion and was similar to an ischemia-reperfusion state. Serum CK and mitotic activity in the muscle consistently increased, and damaged muscle fibers that reacted positively to anti-GPX antibody were also observed after exercise. Serial changes in total SOD, GPX, and CAT activities were biphasic and exhibited peaks immediately and 24-72 h after exercise. The first increase was caused by a repeated ischemia-reperfusion-like state following weight-lifting exercise, and the second was dependent on the accumulation of infiltrated phagocytic cells at the damaged portions. These results suggest that ROS-induced muscle fiber damage occurred as a consequence of weight-lifting exercise.

Application of Near Infrared Spectroscopy to Exercise Sports Science

Over the past 15 years the use of near infrared spectroscopy in exercise and sports science has increased exponentially. The majority of these studies have used this noninvasive technique to provide information related to tissue metabolism during acute exercise. This has been undertaken to determine its utility as a suitable tool to provide new insights into the heterogeneity and regulation of local tissue metabolism, both in cerebral and skeletal muscle tissue. In the accompanying articles in this symposium, issues related to the principles, techniques, limitations (Ferrari et al., 2004), and reliability and validity of NIRS in both cerebral and skeletal muscle tissue (Bhambhani, 2004), mostly during acute exercise, have been addressed and will not be discussed here. Instead, the present paper will focus specifically on the application of NIRS to exercise sports science, with an emphasis on how this technology has been applied to exercise training and sport, and how it can be used to design training programs for athletes. Key words: tissue de-oxygenation, hemoglobin volume, endurance training, resistance exercise, taper, applied physiology

Effect of Muscle Oxygenation during Resistance Exercise on Anabolic Hormone Response

PURPOSE

The mechanisms that underlie the affect of acute program variables on muscle growth and strength development for strength/power athletes have been of great interest. This investigation examined the affects of two different resistance exercise protocols on muscle oxygenation, and the anabolic hormonal response to such exercise.

METHODS

Eleven experienced resistance-trained male athletes performed four sets of the squat exercise using either a low-intensity, high-volume (LI; 15 repetitions at 60% one-repetition maximum [1-RM]) or high-intensity, low-volume (HI; 4 repetitions at 90% 1-RM) load. Venous blood samples were obtained before (Pre), immediate (IP), 20- (20P), and 40-min (40P) postexercise. Continuous-wave near-infrared spectroscopy was used to measure oxygen desaturation during exercise.

RESULTS

No differences in muscle deoxygenation were seen between LI and HI. However, time-dependent postexercise reoxygenation was significantly different between the two exercise sessions (35.3 +/- 17.4 s vs 24.5 +/- 14.3 s in LI and HI, respectively). Testosterone and growth hormone (GH) concentrations were significantly elevated from Pre at IP, 20P, and 40P in both LI and HI. GH concentrations were higher (P<0.05) for LI than at HI at 20P and 40P.

CONCLUSION

Muscle oxygen recovery kinetics appeared to be influenced by differences in the intensity and volume of exercise, and delayed reoxygenation appears to affect the GH response to exercise.

In vivo quantitative near-infrared spectroscopy in skeletal muscle during incremental isometric handgrip exercise

The aim of this study was to investigate the performance of in vivo quantitative near-infrared spectroscopy (NIRS) in skeletal muscle at various workloads. NIRS was used for the quantitative measurement of O2 consumption (mVO2) in the human flexor digitorum superficialis muscle at rest and during rhythmic isometric handgrip exercise in a broad range of work intensities (10-90% MVC=maximum voluntary contraction force). Six subjects were tested on three separate days. No significant differences were found in mVO2 measured over different days with the exception of the highest workload. The within-subject variability for each workload measured over the three measurements days ranged from 15.7 to 25.6% and did not increase at the high workloads. The mVO2 was 0.14 +/- 0.01 mlO2 min-1 100 g-1 at rest and increased roughly 19 times to 2.68 +/- 0.58 mlO2 min-1 100 g-1 at 72% MVC. These results show that local muscle oxygen consumption at rest as well as during exercise at a broad range of work intensities can be measured reliably by NIRS, applied to a uniform selected subject population. This is of great importance as direct local measurement of mVO2 during exercise is not possible with the conventional techniques. The method is robust enough to measure over separate days and at various workloads and can therefore contribute to a better understanding of human physiology in both the normal and pathological state of the muscle.

Muscle oxygenation trends during constant work rate cycle exercise in men and women

PURPOSE

To examine the relationship between muscle oxygenation and arteriovenous oxygen difference [(a - v)O2diff)] at four constant rate workloads in healthy men and women and to compare these responses between the genders.

METHODS

Nineteen men and 14 women consented to perform an incremental test to identify the lactic acidosis threshold (LAT) and maximal aerobic power (VO2max) and an intermittent constant work rate test at an oxygen uptake corresponding to 40% LAT, 80% LAT, 25% LAT-VO2max, and 50% LAT-VO2max. Each exercise interval was 5 min long followed by 2 min of recovery. Cardiac output was measured by CO2 rebreathing at each workload from which (a - v)O2diff was computed. Tissue absorbency was measured from the vastus lateralis in both the test sessions using near infrared spectroscopy (NIRS). Muscle oxygenation during constant work rate exercise and recovery was expressed as a percentage (%Mox) of the maximum range observed during incremental exercise and recovery.

RESULTS

A systematic decrease was observed in %Mox with increasing intensity, followed by a proportional increase during recovery from each exercise bout. Significant inverse relationships were observed between %Mox and (a - v)O2diff in men (r = -0.34) and women (r = -0.31) across the four intensities. Mean %Mox was significantly higher (P < 0.05) in women compared with men, suggesting lesser deoxygenation at the same relative exercise intensity.

CONCLUSIONS

%Mox was not an accurate predictor of mixed (a - v)O2diff during exercise because of the low common variance between these two variables, and it is unclear whether the gender difference in %Mox is a true physiological phenomenon or whether it is an artifact of the NIRS technique.

Oxidative metabolism in muscle

Oxidative metabolism is the dominant source of energy for skeletal muscle. Near-infrared spectroscopy allows the non-invasive measurement of local oxygenation, blood flow and oxygen consumption. Although several muscle studies have been made using various near-infrared optical techniques, it is still difficult to interpret the local muscle metabolism properly. The main findings of near-infrared spectroscopy muscle studies in human physiology and clinical medicine are summarized. The advantages and problems of near-infrared spectroscopy measurements, in resting and exercising skeletal muscles studies, are discussed through some representative examples.

Detection of ventilatory threshold using near infrared spectroscopy in men and women

The onset of anaerobic (lactate) metabolism during incremental exercise, which may be a result of an imbalance between tissue oxygen supply and demand, has been associated with the gas exchange ventilatory threshold (VT). This study was designed to examine whether near infrared spectroscopy (NIRS) could be used to detect the VT in healthy subjects. Twenty-one men and 19 women completed incremental cycle ergometry during which NIRS measurements were obtained from the right vastus lateralis and gas exchange measurements were monitored simultaneously using a metabolic cart. The VT was identified from the metabolic data by the V-slope method and from NIRS data as the intensity at which tissue absorbency crossed the resting baseline value observed immediately prior to the initiation of exercise. Pearson correlations for the relative oxygen uptake and power output observed for the two methods of detecting VT were 0.90 and 0.88, respectively, in men and 0.89 and 0.86, respectively, in women (P < 0.01). No significant differences were observed between the two methods of detecting VT for any of the physiological responses (P > 0.05). No significant (P > 0.05) gender differences were observed in muscle oxygenation values at the VT, 32% in men and 38% in women. These results validate the use of NIRS as an alternate noninvasive method for detecting VT during cycle exercise in healthy subjects.

Dissociated oxygen uptake response to an incremental intermittent repetitive lifting and lowering exercise in humans

Five subjects performed a maximal exercise test of repetitive lifting and lowering, with a discontinuous protocol of incremental exercise (3 min) and relative rest (2 min). Exercise periods consisted of repetitive lifting and repetitive lifting and lowering at increasing movement frequencies. Relative rest periods consisted of ergometer cycling at a constant, low power output. An unexpected, dissociated, response of cardiovascular and pulmonary parameters was found: during relative rest, values for oxygen uptake, carbon dioxide production, pulmonary ventilation and tidal volume were significantly higher than during the preceding exercise periods, though exercise intensity was much lower. To our knowledge, such a response has not been reported in previous studies. Since the response could not be attributed to methodological or technical factors, it is hypothesized that the type of exercise itself impeded the optimal performance of the oxygen transporting system. The function of the pulmonary system could have been influenced by a high intra-abdominal pressure, the involvement of respiratory muscles in stabilizing trunk and head, a flexed trunk posture and the entrainment of respiratory frequency with movement frequency. More likely, the function of the cardiovascular system was hindered by a high blood pressure and high intramuscular pressures. Since this response occurred at low exercise intensities, optimal functioning of the cardiovascular and pulmonary system during daily activities of repetitive lifting and lowering could similarly be impeded. The hypotheses put forward could also explain the lower peak oxygen uptake reported during repetitive lifting, compared to running and cycling.