Key pointsr The concept of symmorphosis predicts that the capacity of each step of the oxygen cascade is attuned to the task demanded of it during aerobic exercise at maximal rates of oxygen consumption (V O 2 max ) such that no single process is limiting or in excess atV O 2 max .r The present study challenges the applicability of this concept to humans by revealing clear, albeit very different, limitations and excesses in oxygen supply and consumption among untrained and endurance-trained humans.r Among untrained individuals,V O 2 max is limited by the capacity of the mitochondria to consume oxygen, despite an excess of oxygen supply, whereas, among trained individuals,V O 2 max is limited by the supply of oxygen to the mitochondria, despite an excess of mitochondrial respiratory capacity. AbstractThe concept of symmorphosis postulates a matching of structural capacity to functional demand within a defined physiological system, regardless of endurance exercise training status. Whether this concept applies to oxygen (O 2 ) supply and demand during maximal skeletal muscle O 2 consumption (V O 2 max ) in humans is unclear. Therefore, in vitro skeletal muscle mitochondrialV O 2 max ( MitoVO 2 max , mitochondrial respiration of fibres biopsied from vastus lateralis) was compared with in vivo skeletal muscleV O 2 max during single leg knee extensor exercise ( KEVO 2 max , direct Fick by femoral arterial and venous blood samples and Doppler ultrasound blood flow measurements) and whole-bodyV O 2 max during cycling ( BodyVO 2 max , indirect calorimetry) in 10 endurance exercise-trained and 10 untrained young males. In untrained subjects, during KE exercise, maximal O 2 supply ( KEQ O 2max ) exceeded (462 ± 37 ml kg −1 min −1 , P < 0.05) and KEVO 2 max matched (340 ± 22 ml kg −1 min −1 , P > 0.05) MitoVO 2 max (364 ± 16 ml kg −1 min −1 ). Conversely, in trained subjects, both KEQ O 2max (557 ± 35 ml kg −1 min −1 ) and KEVO 2 max (458 ± 24 ml kg −1 min −1 ) fell far short of MitoVO 2 max (743 ± 35 ml kg −1 min −1 , P < 0.05). Although MitoVO 2 max was related to KEVO 2 max (r = 0.69, P < 0.05) and BodyVO 2 max (r = 0.91, P < 0.05) in untrained subjects, these variables were entirely unrelated in trained subjects. Therefore, in untrained subjects,V O 2 max is limited by mitochondrial O 2 demand, with evidence of adequate O 2 supply, whereas, in trained subjects, an exercise training-induced mitochondrial reserve results in skeletal muscleV untrained and trained humans and challenge the concept of symmorphosis as it applies to O 2 supply and demand in humans. Abbreviations BIOPS, biopsy preservation fluid; Body, whole-body; KE, knee extensor; Mito, mitochondrial;Q O 2max , maximum specific oxygen uptake rate;V O2max , maximal oxygen uptake; WR max , maximum work rate.

Suspension exercise systems are being used in strength and conditioning facilities, fitness centers, rehabilitation centers and home gyms. Though some evidence exists regarding the impact of training with these systems, more work is needed for a better understanding. The purpose of the present investigation was to examine the acute effects of an exercise session with 2 (hands only) and 4 straps (hands and feet) in the push-up exercise compared to a work-matched bench press exercise session. The participants for this repeated measures, cross-over investigation were 18 healthy college-aged males (age: 24.8 ± 3.5 yrs, body mass: 81.8 ± 7.8 kg, body height: 178.9 ± 4.5 cm). The conditions were 6 sets of 10 repetitions of suspension push-ups using two straps (DUAL) for the hands, fours straps (QUAD) for hands and feet and a traditional bench press exercise matched to the average resistance during the suspension push-up. The participants performed all repetitions at a controlled cadence. Expired gases, and heart rate were monitored continuously during the exercise session. Pre and post exercise saliva samples were collected to quantify changes in testosterone and cortisol. Upper body isometric strength tests ( UBIST) were performed (Post, 1 hr, 24 hr, 48 hr) to evaluate changes in force production during recovery. Data analysis via repeated measures ANOVA revealed a significant trend for increased oxygen consumption in the QUAD condition compared to the bench press (p = 0.019). Additionally, both suspension conditions resulted in a reduced respiratory exchange ratio as compared to the bench press (p < 0.05). A significant main effect was noted for time in all conditions regarding isometric strength (p < 0.001), but no differences between conditions were revealed. Testosterone and cortisol responses did not differ between conditions. Based upon these data, it appears that when matched for work, suspension exercise results in equivalent reductions in muscle force, but greater oxygen consumption compared to isotonic exercise.

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The purpose of this investigation was to examine the effects of a personal oxygen supplement (OS) on performance during exhaustive exercise, respiratory responses during exhaustive exercise, and cognitive function after exhaustive exercise. The participants for this blind placebo-controlled experiment were apparently healthy college-aged adults (n = 20). First, VO2max was assessed (47.6 ± 9.8 ml O2·kg(-1)·min(-1)). Participants then ran 2 trials at 80% of VO2max speed to exhaustion and received either a placebo (compressed air) or personal OS. Psychomotor vigilance testing (PVT) was performed before and after each trial. Performance between treatments was evaluated through repeated measures analysis of variance (ANOVA) and was not found to be different (p = 0.335, ηp2 = 0.052), and order (placebo first or personal OS first) was not significant within the model (p = 0.305, ηp2 = 0.058). Mean times were 1,057.6 ± 619.8 seconds for the oxygen trials and 992.5 ± 463.1 seconds for the placebo trials. Repeated measures ANOVAs were used to assess minute ventilation (Ve, L·min(-1)) and VCO2 (L·O2·min(-1)) during exercise and recovery, mean heart rate during recovery, and PVT results. Treatment was nonsignificant (p > 0.05) nor were any interaction effects (treatment × time, p > 0.05) for any variables. The results of this study suggest that a personal OS had no effect on performance and did not affect ventilation even at the time directly surrounding the application. The results of the study also suggest that personal OS do not enhance exercise recovery or cognition during exercise recovery.