Effects of hypoxia on cerebral and muscle haemodynamics during knee extensions in healthy subjects.

A hypoxic model was used to investigate changes in localized cerebral and muscle haemodynamics during knee extension (KE) in healthy individuals. Thirty-one young healthy volunteers performed one set of KE until failure under hypoxia (14 % O(2)) or normoxia (21 % O(2)) at 50, 75 or 100 % of 1 repetition maximum, in random order, on three occasions. Prefrontal cerebral and vastus lateralis muscle oxygenation and blood volume (Cox, Mox, Cbv and Mbv, respectively) were recorded simultaneously by near-infrared spectroscopy. Hypoxia induced significant declines in Cox [-0.017 ± 0.016 optical density (OD) units] and Mox (-0.014 ± 0.026 OD units) and increases in Cbv (0.017 ± 0.027 OD units) and Mbv (0.016 ± 0.023 OD units) at rest. Hypoxia significantly reduced total work (TW) performed during KE at each exercise intensity. Cox, Cbv, Mox, and Mbv changes during KE did not differ between normoxia and hypoxia. Correlations between TW done and Cox changes under normoxia (r = 0.04, p = 0.182) and hypoxia (r = 0.05, p = 0.122) were not significant. However, TW was significantly correlated with Mox under both normoxia (R (2) = 0.24, p = 0.000) and hypoxia (R (2) = 0.15, p = 0.004). Since changes in Cox and Mox reflect alterations in the balance between oxygen delivery and extraction in these tissues, which, in the brain, is an index of neuronal activation, we conclude that: (1) limitation of KE performance was mediated peripherally under both normoxia and hypoxia, with no additional effect of hypoxia, and (2) because of the low common variance with Mox additional intramuscular factors likely play a role in limiting KE performance.

Serial monitoring of CO2 reactivity following sport concussion using hypocapnia and hypercapnia.

PRIMARY OBJECTIVE: This study examined the effects of mild traumatic brain injury (mTBI) on cerebrovascular reactivity (CVR). RESEARCH DESIGN: A repeated measures design was used to examine serial changes in CVR. METHODS AND PROCEDURES: Twenty subjects who recently suffered a mTBI were subjected to a respiratory challenge consisting of repeated 20 s breath-holds (BH) and hyperventilations (HV). Testing occurred on days 2 (D2), 4 (D4) and 8 (D8) post-injury as well as a baseline (BASE) assessment (after return-to-play). Transcranial Doppler was used to assess mean cerebral blood velocity (vMCA) and expired gas analysis provided end-tidal carbon dioxide (PETCO2) levels. RESULTS: There was no significant difference in resting vMCA across all testing days for mTBI. No significant differences in PETCO2 were found throughout the testing protocol. A significant effect (p < 0.001) of testing day on vMCA was found during BH and HV challenges for mTBI. Post-hoc analysis revealed significant differences (p < 0.05) in vMCA between D2 and the other testing days. CONCLUSIONS: These data suggest that, following mTBI: (1) CVR is not impaired at rest; (2) CVR is impaired in response to respiratory stress; and (3) the impairment may be resolved as early as 4 days post-injury.

Pre-frontal Cortex Oxygenation Changes During Aerobic Exercise in Elite Athletes Experiencing Sport-Related Concussion.

Aims: Recent research suggests that aerobic exercise can be performed safely within the first week following a concussion injury and that early initiation of exercise may speed recovery. To better understand the physiological changes during a concussion, we tested the hypothesis that mild-to-intense exercise testing can be performed within days immediately following injury, and can be used to discern differences between the concussed and normal healthy state. Thus, the purpose was to observe the cerebral hemodynamic responses to incremental exercise testing performed acutely post-concussion in high-performance athletes. Methods: This study was a within- and between-experimental design, with seven male university ice hockey teams participating. A subgroup of five players acted as control subjects (CON) and was tested at the same time as the 14 concussed (mTBI) players on Day 2, 4, and 7 post-concussion. A 5-min resting baseline and 5-min exercise bouts of mild (EX1), moderate (EX2), and high (EX3) intensity exercise were performed on a cycle ergometer. Near-infrared spectroscopy was used to monitor pre-frontal cortex oxy-haemoglobin (HbO2), deoxy-haemoglobin (HHb), and total blood volume (tHb) changes. Results: ANOVA compared differences between testing days and groups, and although large percentage changes in HbO2 (20-30%), HHb (30-40%), and tHb (30-40%) were recorded, no significant (p ≤ 0.05) differences in cerebral hemodynamics occurred between mTBI vs. CON during aerobic exercise testing on any day post-injury. Furthermore, there was a linear relationship between exercise intensity vs. cerebral hemodynamics during testing for each day (r 2 = 0.83-0.99). Conclusion: These results demonstrate two novel findings: (1) mild-to-intense aerobic exercise testing can be performed safely as early as Day 2 post-concussion injury in a controlled laboratory environment; and (2) evidence-based objective measures such as cerebral hemodynamics can easily be collected using near-infrared spectroscopy (NIRS) to monitor physiological changes during the first-week post-injury. This research has important implications for monitoring physiological recovery post-injury and establishing new rehabilitation guidelines.

Microvascularity of the lumbar erector spinae muscle during sustained prone trunk extension test.

This study evaluated the reliability of oxygenation and blood volume responses, from the right erector spinae in twenty two healthy men and women, during static prone trunk extension on two separate days. Near-infrared spectroscopy (NIRS)-derived physiological change for oxygenation was calculated as the difference between the 'baseline' before the start of the trunk extension and 'minimum' at the point of volitional exhaustion. The physiological change for blood volume was calculated as the difference between the 'baseline' value and 'maximum' at the point of volitional exhaustion. Test-retest reliability, based on the intraclass correlation coefficients for the physiological change were: oxygenation--men: +0.60 versus women: +0.37; blood volume--men: +0.93 versus women: +0.59, respectively. Results suggest that NIRS-derived blood volume measurements were more reliable than the oxygenation responses. The most interesting observation of the study was the hyperemia in blood volume responses with a parallel decrease in oxygenation as participants continued the test until volitional exhaustion. Such an increase in muscle blood volume contradicts the theory that sufficient occlusion of blood flow to the lumbar muscle region is possible with static trunk extension resulting in muscle fatigue.

Functional changes in cerebral and paraspinal muscle physiology of healthy women during exposure to whole-body vibration.

The objective of this study was to investigate the effects of whole-body vibration on multiple tissues simultaneously in fourteen healthy women. On three separate days, participants were exposed to frequencies, 3, 4.5, or 6 Hz (at 0.9 g(r.m.s) acceleration in vertical direction) per day on a simulator for 16 min. While sitting 'with' and 'without' backrest support, participants also performed handgrip contractions for 1 min. Cerebral and lumbar muscle oxygenation and blood volume responses were measured using near-infrared spectroscopy. Cardiorespiratory responses were collected using a metabolic cart. In general, cerebral and cardiorespiratory responses increased with vibration compared to without vibration, whereas in the lumbar region oxygenation and blood volume responses decreased. Greatest cerebral responses were observed at 6 Hz (P<0.05). When compared to exposure to vibration without performing work, significant decrease in lumbar responses was observed during handgrip contractions in both conditions of sitting 'with' and 'without' a backrest (P<0.05). Such decreases in the lumbar responses suggest postural load due to prolonged sitting combined with physical activity during vibration, might reduce vascular supply to the paraspinal muscles. This study reiterates the importance of understanding the physiological basis for various health disorders in women due to exposure to whole-body vibration.

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.

Peripheral circulatory responses in vivo from regional brachial biceps and lumbar muscles in healthy men and women during pushing and pulling exercise.

BACKGROUND: Although women have been performing increasingly more manual labor in the workplace in the past 2 decades, their physiological responses and gender-based differences in muscle microvascularity during occupational activities have not yet been extensively documented. OBJECTIVE: This study assessed gender differences and tissue heterogeneity in peripheral circulatory responses from 2 muscle groups during pushing and pulling exercise until volitional exhaustion. METHODS: In healthy men and women, near-infrared spectroscopy was used to determine peripheral responses, oxygenation, and blood volume simultaneously from the right biceps brachii and lumbar erector spinae. Pulmonary oxygen uptake was assessed using a metabolic measurement cart. RESULTS: Although the 11 men who participated in the study demonstrated greater pulmonary oxygen uptake and power output at volitional exhaustion, their peak peripheral responses for both muscles were similar to those of the 11 women participating. In both sexes, oxygenations trends decreased in both muscles with an increase in workload. However, whereas blood volume increased in the biceps, it decreased in the lumbar muscle in both sexes. At 20% to 60% levels of peak pulmonary oxygen uptake, the percent change in peripheral bicep responses was greater for men than for women (P < 0.05). In contrast, women demonstrated greater change in lumbar muscle oxygenation compared with men at 40% to 60% of peak pulmonary oxygen uptake (P < 0.05). CONCLUSIONS: Similar peripheral responses for biceps and lumbar muscles at the point of volitional exhaustion suggest that gender differences in pulmonary oxygen uptake are independent of oxygen extraction or delivery across the muscle groups monitored. However, at submaximal levels of exercise, the peripheral changes in each muscle were gender dependent. Although biceps and lumbar muscles are 2 discrete muscle groups, based on the heterogeneity found in the blood volume trends it is likely that oxygen supply and demand are regulated by muscle location and muscle fiber characteristics. Overall, gender-based assessment of occupational activities should incorporate both pulmonary and peripheral circulatory responses to understand each sex's performance effectiveness.

Muscle oxygenation trends after tapering in trained cyclists.

BACKGROUND: This study examined muscle deoxygenation trends before and after a 7-day taper using non-invasive near infrared spectroscopy (NIRS). METHODS: Eleven cyclists performed an incremental cycle ergometer test to determine maximal oxygen consumption (VO2max = 4.68 +/- 0.57 L.min-1) prior to the study, and then completed two or three high intensity (85-90% VO2max) taper protocols after being randomly assigned to a taper group: T30 (n = 5), T50 (n = 5), or T80 (n = 5) [30%, 50%, 80% reduction in training volume, respectively]. Physiological measurements were recorded during a simulated 20 km time trials (20TT) performed on a set of wind-loaded rollers. RESULTS AND DISCUSSION: The results showed that the physiological variables of oxygen consumption (VO2), carbon dioxide (VCO2) and heart rate (HR) were not significantly different after tapering, except for a decreased ventilatory equivalent for oxygen (VE/VO2) in T50 (p

Effects of short-term endurance training on muscle deoxygenation trends using NIRS.

PURPOSE: This study examined changes in cardiorespiratory responses and muscle deoxygenation trends to test the hypothesis that both central and peripheral adaptations would contribute to the improvements in VO(2max) and simulated cycling performance after short-term high-intensity training. METHODS: Eight male cyclists performed an incremental cycle ergometer test to voluntary exhaustion, and a simulated 20-km time trial (20TT) on wind-loaded rollers before and after training (60 min x 5 d x wk(-1) x 3 wk at 85-90% VO(2max). Near-infrared spectroscopy (NIRS) was used to evaluate the trend in vastus medialis hemoglobin/myoglobin deoxygenation (Hb/Mb-O(2) during both tests pre- and post-training. RESULTS: Training induced significant increases (P 0.05) in the VO(2) (4.02 +/- 0.52 to 4.04 +/- 0.51), heart rate (176 +/- 9 to 173 +/- 8 beats x min ) or O pulse (22.4 +/- 3.2 to 23.5 +/- 2.8 mL O(2) x beat(-1)). However, mean muscle deoxygenation during the 20TT was significantly lower after training (-550 +/- 292 to -707 +/- 227 mV, P

Acute l-arginine supplementation increases muscle blood volume but not strength performance.

l-Arginine (L-arg) is an amino acid precursor to nitric oxide (NO). Dietary supplements containing L-arg have been marketed with the purpose of increasing vasodilation, thereby elevating blood flow to the exercising muscle and enhancing the metabolic response to exercise. Our goal was to identify the acute effect of L-arg supplementation on biceps strength performance, indicators of NO production (nitrite and nitrate - NOx), and muscle blood volume (Mbv) and oxygenation (Mox) during recovery from 3 sets of resistance exercise. Fifteen males participated in a randomized, double-blind, placebo-controlled study. After withdrawing resting blood samples, the subjects were supplemented with 6 g of L-arg (ARG) or placebo (PLA). Monitoring of Mbv and Mox with near-infrared spectroscopy began 30 min after supplementation and lasted for 60 min. The exercise protocol (3 sets of 10 maximal voluntary contractions of isokinetic concentric elbow extension at 60°·s(-1), 2-min rest between sets) was initiated 80 min after supplementation. Blood samples were drawn at 30, 60, 90, and 120 min after supplementation. Repeated measures ANOVA showed that Mbv significantly (p ≤ 0.05) increased in ARG compared with the PLA during the recovery period of each set of resistance exercise. NOx, Mox, peak torque, total work, and set total work were not significantly different between groups. We found that acute L-arg supplementation increases Mbv during recovery from sets of resistance exercise with no increase in strength performance. It is still premature to recommend nutritional supplements containing L-arg as an ergogenic aid to increase muscle strength during resistance training in healthy subjects.

L-Arginine as a potential ergogenic aid in healthy subjects.

Dietary supplements containing L-arginine, a semi-essential amino acid, are one of the latest ergogenic aids intended to enhance strength, power and muscle recovery associated with both aerobic and resistance exercise. L-arginine is claimed to promote vasodilation by increasing nitric oxide (NO) production in the active muscle during exercise, improving strength, power and muscular recovery through increased substrate utilization and metabolite removal, such as lactate and ammonia. Research on L-arginine has recently tested this hypothesis, under the assumption that it may be the active compound associated with the vasodilator effects of NO. There were only five acute studies retrieved from the literature that evaluated exercise performance after L-arginine supplementation, three of which reported significant improvements. Regarding studies on chronic effects, eight studies were encountered: four reported enhancements in exercise performance, whilst four reports showed no changes. Whether these improvements in exercise performance - regardless of the aerobic or anaerobic nature of the exercise - can be associated with increases in NO production, has yet to be demonstrated in future studies. Low oral doses (≤20 g) are well tolerated and clinical side effects are rare in healthy subjects. In summary, it is still premature to recommend dietary supplements containing L-arginine as an ergogenic aid for healthy physically active subjects.

Cerebrovascular reactivity impairment after sport-induced concussion.

PURPOSE: This study evaluated cerebrovascular reactivity (CVR) after a sport-induced concussion, also called mild traumatic brain injury (mTBI), by monitoring middle cerebral artery blood velocity (vMCA) with transcranial Doppler ultrasonography and simultaneous end-tidal carbon dioxide (PETCO(2)) measurements. METHODS: Thirty-one athletes (16-25 yr old) participated in this study. The participants were divided into two groups-healthy (n = 21) and mTBI (n = 10). Participants in the mTBI group suffered an mTBI within the last 7 d (x- = 4.5 ± 1.1 d). Outcome measures included vMCA and PETCO(2) in response to breath holding (5 × 20 s, 40-s rest) and hyperventilation (5 × 20 s, 40-s rest). RESULTS: Resting vMCA values between groups were not significantly different. Percentage change of vMCA was significantly different after the recovery period of the second hyperventilation (P = 0.034). mTBI subjects failed to return to resting levels after each breath hold. PETCO(2) changes mirrored the vMCA changes. CONCLUSIONS: These data suggest that normal CVR responses may be disrupted in the days immediately after occurrence of mTBI. Transcranial Doppler ultrasonography combined with expired gas measurements provides a useful method for assessing CVR impairment after mTBI. Further research, including serial monitoring after mTBI and analysis of CVR response to exercise, is warranted before any firm conclusions can be drawn.

Acute effects of sustained isometric knee extension on cerebral and muscle oxygenation responses.

Cerebral contra-lateral frontal lobe and the dominant vastus lateralis muscle oxygenation (Cox, Mox) and blood volume (Cbv, Mbv) were recorded simultaneously using near infrared spectroscopy (NIRS) in 12 healthy volunteers (37.4 +/- 9.9 years; 72.3 +/- 16.1 kg; 171.0 +/- 9.6 cm) during 2 min resting baseline, an isometric knee extension with the 1 RM load sustained to the point of fatigue, and 3 min recovery. The mean exercise duration was 19.1 +/- 2.6 s. During the contraction, Cox and Cbv increased systematically with no sign of levelling off until the point of fatigue. In contrast, Mox and Mbv declined continuously until the termination of exercise. Qualitative analysis of these NIRS profiles suggested that maximal isometric performance under normoxic conditions was most likely not limited by central neuronal activation, but rather, was due to factors within the exercising muscle. It is likely that depletion of intramuscular stores of high energy phosphates and oxymyoglobin, as well as the accumulation of metabolites from anaerobic pathways, were implicated in fatigue during this sustained high intensity isometric contraction.

Comparisons of physiological and perceptual responses in healthy men and women during standardized arm cranking and task-specific pushing-pulling.

OBJECTIVE: Peak cardiorespiratory, metabolic, and perceptual responses in healthy men (n=11) and women (n=11) were compared during two different upper body exercise modes: standardized arm cranking and task-specific pushing-pulling. METHODS: Each subject completed to volitional exhaustion both an incremental arm cranking and a pushing-pulling exercise continuously, in a random order, on two separate days. Physiological responses were monitored using an automated metabolic cart and a heart rate monitor, and the rating of perceived exertion was obtained using a 15-point Borg Scale. RESULTS: Peak oxygen uptake, oxygen pulse, respiratory exchange ratio, and ventilation rate were higher and total exercise time to exhaustion was lower during arm cranking compared to pushing-pulling (P<0.05). However, heart rate was similar between exercise modes (P>0.05). Men showed greater physiological responses (absolute oxygen uptake, oxygen pulse, and ventilation rate) and longer exercise time to exhaustion than women (P<0.05). Power output during arm cranking was higher (by 79%) than pushing-pulling (P<0.01), with men demonstrating 30% greater values during both exercise modes (P<0.01). The lower power output generated during pushing-pulling resulted in a greater ratio of peak oxygen uptake to power output (by 72%; P<0.05). Interestingly, although power output and oxygen uptake were lower at the maximal workload, perceived exertion was higher (by 5%) during pushing-pulling (P<0.05). CONCLUSIONS: Based on the physiological differences, pushing-pulling is found to be metabolically less efficient than arm cranking. However, greater ratings of perceived exertion during pushing-pulling implies that the perception of effort can also be influenced by a low intensity task, such as pushing-pulling, if performed for a prolonged period. Occupational health professionals should be aware of the limitations of utilizing physiological and perceptual responses obtained only from standardized ergometric protocols in predicting the workers' performance effectiveness.

In vivo lumbar erector spinae oxygenation and blood volume measurements in healthy men during seated whole-body vibration.

Exposure to whole-body vibration is implicated as one of the occupational risk factors for lower back disorders; however, its influence on the lumbar muscle physiology is still poorly understood. The objective of this study was to investigate the effects of backrest support and hand grip contractions on lumbar muscle oxygenation and blood volume responses during seated whole-body vibration using continuous dual-wave near-infrared spectroscopy. Thirteen healthy men were exposed to frequencies of 3, 4.5 and 6 Hz on a vibration simulator, in randomized order on separate days. Each day the duration of the protocol was 30 min. During the fifth minute of vibration 'with' and 'without' backrest support, participants performed maximal rhythmic hand grip contractions for 1 min. In general, erector spinae oxygenation and blood volume showed a trend to decrease with vibration exposure compared to the control condition. However, these responses were not influenced by the change in vibration frequency (P > 0.05). Sitting without backrest resulted in a greater decrease in oxygenation (by 27%, P = 0.02) and blood volume (by 11%, P = 0.05) than with backrest, implying a deficiency in oxygen supply owing to the sitting posture. Compared to the vibration-only condition, hand grip work decreased both oxygenation (by 22%, P = 0.003) and blood volume responses (by 13%, P = 0.04), suggesting that postural load due to prolonged sitting combined with physical activity during vibration might further burden paraspinal muscles. The influence of adipose tissue thickness of the lumbar muscle on optically derived oxygenation and blood volume changes was inconclusive.

Acute physiological responses in healthy men during whole-body vibration.

OBJECTIVE: The influence of backrest support and handgrip contractions on acute metabolic, respiratory, and cardiovascular responses were evaluated in 13 healthy men during exposure to whole-body vibration (WBV). METHODS: Following assessment of aerobic fitness during arm cranking, subjects were exposed to frequencies 3, 4.5, and 6 Hz with 0.9 g(r.m.s) acceleration magnitude on a vibrating base in randomized order, on separate days. Each exposure included 6 min baseline without WBV, 8 min of WBV exposure either 'with' or 'without' backrest, 4 min recovery, followed by 8 min of WBV with opposite backrest condition, and 4 min recovery. During the final minute of WBV, subjects performed right hand maximal rhythmic handgrip contractions for one minute. During baseline and before completion of WBV session 'with' and 'without' backrest, cardiac output was estimated indirectly by carbon dioxide rebreathing. RESULTS: At 3 and 4.5, and 3 and 6 Hz, absolute and relative oxygen uptake demonstrated significantly greater responses during sitting 'without' backrest than 'with' backrest (P<0.01). At 3 and 4.5 Hz, heart rate and oxygen pulse responses were significantly greater during WBV combined with handgrip contractions than during WBV alone (P<0.01), demonstrating physical work during WBV will enhance greater metabolic responses. Stroke volume was the lowest at 4.5 Hz (P<0.01). Influence of aerobic fitness was evident only in absolute oxygen uptake, oxygen pulse, and ventilation volume (P<0.01). CONCLUSIONS: This study demonstrates that subjects exposed to physical work during WBV will experience greater metabolic responses compared to WBV alone, and the physiological responses during WBV resemble to that of a light physical work. Despite low metabolic rates during WBV, the effect of aerobic fitness suggests the importance of physical activity in occupations exposed to WBV.

Cerebral oxygenation and blood volume responses to seated whole-body vibration.

Role of backrest support and hand grip contractions on regional cerebral oxygenation and blood volume were evaluated by near infrared spectroscopy in 13 healthy men during whole-body vibration (WBV). Subjects were exposed to three WBV (3, 4.5, and 6 Hz at approximately 0.9 g(rms) in the vertical direction), in a randomized order on separate days. During WBV, subjects performed right-hand maximal voluntary intermittent rhythmic hand grip contractions for 1 min. Subjects demonstrated highest oxygenation and blood volume values at 4.5 Hz, however, these responses were similar with and without backrest support (P>0.01). Compared to WBV alone, addition of hand grip exercise during WBV further increased oxygenation (0.07+/-0.11 vs. 0.004+/-0.11 od, P=0.003) and blood volume (0.156+/-0.20 vs. 0.066+/-0.17 od, P=0.000) in the right forehead. Peak oxygen uptake did not correlate to changes in oxygenation and blood volume (P>0.01). Based on the increase in ventilation volume and no change in the ratio of ventilation volume and expired carbon dioxide (P>0.01), it is concluded that WBV induces hyperventilation that might activate the pre-frontal cortical region, thus influencing cerebral responses through neuronal activation.

Muscle oxygenation trends during dynamic exercise measured by near infrared spectroscopy.

During the last decade, NIRS has been used extensively to evaluate the changes in muscle oxygenation and blood volume during a variety of exercise modes. The important findings from this research are as follows: (a) There is a strong correlation between the lactate (ventilatory) threshold during incremental cycle exercise and the exaggerated reduction in muscle oxygenation measured by NIRS. (b) The delay in steady-state oxygen uptake during constant work rate exercise at intensities above the lactate/ventilatory threshold is closely related to changes in muscle oxygenation measured by NIRS. (c) The degree of muscle deoxygenation at the same absolute oxygen uptake is significantly lower in older persons compared younger persons; however, these changes are negated when muscle oxygenation is expressed relative to maximal oxygen uptake values. (d) There is no significant difference between the rate of biceps brachii and vastus lateralis deoxygenation during arm cranking and leg cycling exercise, respectively, in males and females. (e) Muscle deoxygenation trends recorded during short duration, high-intensity exercise such as the Wingate test indicate that there is a substantial degree of aerobic metabolism during such exercise. Recent studies that have used NIRS at multiple sites, such as brain and muscle tissue, provide useful information pertaining to the regional changes in oxygen availability in these tissues during dynamic exercise.

Effects of different stepwise reduction taper protocols on cycling performance.

This study examined the effects of different 7-day taper protocols on simulated 20-km time trials (20TT). Following 3 weeks of baseline training, 11 male cyclists (.VO2max = 4.78 +/- 0.66 L.min-1) were randomly assigned to one of three stepwise reduction tapers in which training volume was reduced by 30% (T30, n = 5), 50% (T50, n = 6), or 80% (T80, n = 6) of baseline training with intensity (85% .VO2max) maintained. Cardiorespiratory measurements were collected every 5 km during the 20TT. Results revealed a significant (5.4%, 0.05) improvement in 20TT performance in the T50 protocol with concomitant increases in .VO2 and O2 pulse. No significant differences were found in T30 or T80. These results showed that a moderate (50%) reduction in weekly training volume appeared to be optimal in terms of enhancing performance. This confirms the contention that proper placement of training volume during tapering, while maintaining exercise intensity, can elicit performance improvements.

Monitoring individual erector spinae fatigue responses using electromyography and near infrared spectroscopy.

This study examined the utility of electromyography and near-infrared spectroscopy (NIRS) in assessing m. erector spinae activity during the Biering-Sorensen Back Muscle Endurance (BSME) test. Six men and four women (27.0 +/- 7.1 years of age) performed the BSME test (time = 131.5 +/- 43.5 s). EMG was used to quantify neuromuscular activity of the right and left side at the L3 level, and root mean square was scaled for maximum value at the start of the exercise. NIRS was used to evaluate blood volume (BV) and oxygenation (OX) simultaneous with EMG bilaterally at the L3 level. There was a decrease to 49+/- 8% of initial median frequency (mean= 83 Hz) on both right and left sides when the exercise was 90% complete, and the slope of the median frequency/time relationship was significantly related to BSME time (r = 0.82). Group means for BV increased during back exercise while OX decreased and was significantly different between right and left sides of the lower back. However, large OX response differences among individuals and between right and left sides were noted. OX and median frequency were moderately related (r = 0.27-0.38). It appears that NIRS combined with EMG is a promising tool for assessing localized metabolic and neuromuscular activity during static contractions of the lower back.