High lactate and NH3 release during arm vs. leg exercise is not due to beta-adrenoceptor stimulation

The effect of age and sex on peak oxygen uptake during upper and lower body exercise: A systematic review

BACKGROUND

Large scale population norms for peak oxygen uptake (VO2peak) during cycle ergometry (CE) have been published for men and women across a wide range of ages. Although upper body functional capacity has an important role in activities of daily living far less is known regarding the effect of age and sex on upper body functional capacity (i.e. arm crank ergometry; ACE). The aim of this review was to determine the effect of age and sex on VO2peak obtained during ACE and CE in the same participants.

METHOD

The review was pre-registered with PROSEPERO (Ref: CRD42022349566). A database search using Academic Search Complete including CINAHL complete, CINHAL Ultimate, Medline, PubMed, SPORTDiscus was undertaken.

RESULTS

The initial search yielded 460 articles which was reduced to 243 articles following removal of duplicates. Twenty-five articles were subsequently excluded based on title resulting in 218 articles considered for retrieval. Following review of the abstracts, 78 further articles were excluded leaving 140 to be assessed for eligibility. Eighty-five articles were subsequently excluded, resulting in 55 articles being included. The decrease in VO2peak with age during CE was consistent with previous studies. Decreases in VO2peak during ACE with age, although paralleling those of CE, appeared to be of greater functional importance. When changes in VO2peak were considered below the age of 50 years little change was observed for absolute VO2peak during ACE and CE. In contrast, relative VO2peak demonstrated decreases in VO2peak for both ACE and CE likely reflecting increases in body mass and body fat percentage with age. After 50 years of age absolute and relative VO2peak demonstrated more similar and subtle responses. Heterogeneity across studies for both absolute and relative VO2peak between ACE and CE was large. Although strict inclusion criteria were applied, the inter-individual variation in sample populations was likely the main source of heterogeneity. There was a considerable lack data sets available for ages above 40 years of age.

CONCLUSIONS

These responses suggest that upper body VO2peak decreases in line with that of the lower body but, due to the lower peak values achieved during ACE, decreases in VO2peak may have more profound functional impact compared to that for the lower body. Using absolute and relative measures of VO2peak results in different age-related profiles when considered below 50 years of age. To further our understanding of whole body ageing more data is required for participants in mid and later life. The association between VO2peak and underlying physiological factors with age needs to be studied further, particularly in conjunction with activities of daily living and independent living.

Cardiovascular control during whole body exercise

It has been considered whether during whole body exercise the increase in cardiac output is large enough to support skeletal muscle blood flow. This review addresses four lines of evidence for a flow limitation to skeletal muscles during whole body exercise. First, even though during exercise the blood flow achieved by the arms is lower than that achieved by the legs (∼160 vs. ∼385 ml·min(-1)·100 g(-1)), the muscle mass that can be perfused with such flow is limited by the capacity to increase cardiac output (42 l/min, highest recorded value). Secondly, activation of the exercise pressor reflex during fatiguing work with one muscle group limits flow to other muscle groups. Another line of evidence comes from evaluation of regional blood flow during exercise where there is a discrepancy between flow to a muscle group when it is working exclusively and when it works together with other muscles. Finally, regulation of peripheral resistance by sympathetic vasoconstriction in active muscles by the arterial baroreflex is critical for blood pressure regulation during exercise. Together, these findings indicate that during whole body exercise muscle blood flow is subordinate to the control of blood pressure.

Quantification of skeletal muscle mitochondrial function by 31P magnetic resonance spectroscopy techniques: a quantitative review

Magnetic resonance spectroscopy (MRS) can give information about cellular metabolism in vivo which is difficult to obtain in other ways. In skeletal muscle, non-invasive (31) P MRS measurements of the post-exercise recovery kinetics of pH, [PCr], [Pi] and [ADP] contain valuable information about muscle mitochondrial function and cellular pH homeostasis in vivo, but quantitative interpretation depends on understanding the underlying physiology. Here, by giving examples of the analysis of (31) P MRS recovery data, by some simple computational simulation, and by extensively comparing data from published studies using both (31) P MRS and invasive direct measurements of muscle O2 consumption in a common analytical framework, we consider what can be learnt quantitatively about mitochondrial metabolism in skeletal muscle using MRS-based methodology. We explore some technical and conceptual limitations of current methods, and point out some aspects of the physiology which are still incompletely understood.

Arm and leg substrate utilization and muscle adaptation after prolonged low-intensity training

This review will focus on current data where substrate metabolism in arm and leg muscle is investigated and discuss the presence of higher carbohydrate oxidation and lactate release observed during arm compared with leg exercise. Furthermore, a basis for a possible difference in substrate partitioning between endogenous and exogenous substrate during arm and leg exercise will be debated. Moreover the review will probe if differences between arm and leg muscle are merely a result of different training status rather than a qualitative difference in limb substrate regulation. Along this line the review will address the available studies on low-intensity training performed separately with arm or legs or as whole-body training to evaluate if this leads to different adaptations in arm and leg muscle resulting in different substrate utilization patterns during separate arm or leg exercise at comparable workloads. Finally, the influence and capacity of low-intensity training to influence metabolic fitness in the face of a limited effect on aerobic fitness will be challenged.

Local and systemic effects on blood lactate concentration during exercise with small and large muscle groups

To evaluate the relationship between lactate release and [lac](art) and to investigate the influence of the catecholamines on the lactate release, 14 healthy men [age 25+/-3 (SE) year] were studied by superimposing cycle on forearm exercise, both at 65% of their maximal power reached in respective incremental tests. Handgrip exercise was performed for 30 min at 65% of peak power. In addition, between the tenth and the 22nd minute, cycling with the same intensity was superimposed. The increase in venous lactate concentration ([lac](ven)) (rest: 1.3+/-0.4 mmol.l(-1); 3rd min: 3.9+/-0.8 mmol.l(-1)) begins with the forearm exercise, whereas arterial lactate concentration ([lac](art)) remains almost unchanged. Once cycling has been added to forearm exercise (COMB), [lac](art) increases with a concomitant increase in [lac](ven) (12th min: [lac](art), 3.2+/-1.3 mmol.l(-1); [lac](ven), 5.7+/-2.2 mmol.l(-1)). A correlation between oxygen tension (P(v)O(2)) and [lac](ven) cannot be detected. There is a significant correlation between [lac](art) and norepinephrine ([NE]) (y=0.25x+1.2; r=0.815; p<0.01) but no correlation between lactate release and epinephrine ([EPI]) at moderate intensity. Our main conclusion is that lactate release from exercising muscles at moderate intensities is neither dependent on P(v)O(2) nor on [EPI] in the blood.

Effect of hypoxia on muscle oxygenation and metabolism during arm exercise in humans

The influence of hypoxaemia on anaerobic energy production during arm exercise (AE) has been investigated. Six men were studied during maximal AE and during 10 min of sitting submaximal AE under both normoxic (AEN) and hypoxic (AEH, respiratory hypoxia, 12% O2) conditions. Peak pulmonary oxygen uptake (VO2) during maximal AE in normoxia and hypoxia was 2.25 +/- 0.15 and 2.18 +/- 0.14 l min-1, respectively (P < 0.05). The absolute workload was the same during submaximal AEN and AEH and corresponded to 54% of peak VO2 during normoxic maximal AE. To eliminate the potential influence of differences in catecholamine levels on the metabolic response, the submaximal experiments were performed during beta-adrenoceptor blockade. Oxygen deficit was 1.45 +/- 0.26 and 1.67 +/- 0.191 during AEN and AEH, respectively (n.s.). Oxygen extraction at steady state was lower during AEH than during AEN, and assuming a similar O2 demand this corresponds to a 14% higher muscle blood flow during AEH. At the onset of both AEN and AEH, O2 extraction (a-v O2) across the arm increased transiently above that at steady state, the increase being more pronounced during AEN than during AEH (P < 0.05). Muscle oxygenation, measured by near-infrared spectroscopy, demonstrated an initial decrease which was partially reversed as exercise proceeded. The reversal of muscle O2 desaturation was slower in all subjects during AEH (t1/2 = 2.4 +/- 0.2 min) than during AEN (t1/2 = 1.2 +/- 0.2 min; P < 0.01). After 10 min of exercise, arterial blood lactate was higher (P < 0.05) during AEH (5.5 +/- 0.2 mmol l-1) than during AEN (4.9 +/- 0.6 mmol l-1), whereas arterial plasma ammonia (NH3) was similar. The arteriovenous difference for both lactate and ammonia was similar during AEN and AEH. It is concluded that the high anaerobic energy production at the onset of AE is associated with a transient increase in O2 extraction and a transient decrease in muscle oxygenation. The effects of hypoxaemia on peak VO2, oxygen deficit and blood metabolites are less pronounced than previously described during submaximal leg exercise (LE).

Effect of muscle mass on lactate formation during exercise in humans

To elucidate the mechanisms of lactate formation during submaximal exercise, eight men were studied during one- (1-LE) and two-leg (2-LE) exercise (approximately 11-min cycling) using the catheterization technique and muscle biopsies (quadriceps femoris muscle). The absolute exercise intensity and thus the energy demand for the exercising limb was the same [mean 114 (SEM 7) W] during both 1-LE and 2-LE. At the end of exercise partial pressure of O2 and O2 saturation in femoral venous blood were lower and arterial adrenaline and noradrenaline were higher during 2-LE than during 1-LE. Mean arterial blood lactate concentration increased to 10.8 (SEM 0.8) (2-LE) and 5.2 (SEM 0.4) mmol.l-1 (1-LE) after 10 min of exercise. The intramuscular metabolic response to exercise was attenuated during 1-LE [mean, lactate = 49 (SEM 9); glucose 6-P = 3.3 (SEM 0.3); nicotinamide adenine dinucleotide, reduced = 0.17 (SEM 0.02); adenosine 5'-diphosphate 2.7 (SEM 0.1) mmol.kg dry mass-1] compared to 2-LE [76 (SEM 6); 6.1 (SEM 0.7); 0.21 (SEM 0.02); 3.0 (SEM 0.1) mmol.kg dry mass-1, respectively]. To elucidate whether the lower plasma adrenaline concentration could contribute to the attenuated metabolic response, additional experiments were performed on four of the eight subjects with infusion of adrenaline during 1-LE (1-LEE). Average plasma adrenaline concentration was increased during 1-LEE and reached 2-4 times higher levels than during 2-LE. Post-exercise muscle lactate and glucose 6-P contents were higher during 1-LEE than during 1-LE and were similar to those during 2-LE.(ABSTRACT TRUNCATED AT 250 WORDS)