Index of mechanical efficiency in competitive and recreational long distance runners.

The purpose of this investigation was to compare external work and net energy expenditure during a bout of repetitive stretch-shortening cycles between competitive and recreational long-distance runners. Participants were divided into either competitive or recreational runners based on their maximal oxygen consumption and self-reported 1600 m times. The stretch-shortening cycle involved a repetitive hopping protocol on a force plate while measuring oxygen consumption and lactate accumulation for a total of 10 min. External work and net energy expenditure were calculated for 3 min after steady state was achieved and the ratio between these variables was utilised as an index of mechanical efficiency. Lower extremity stiffness was calculated during this interval as well. Net energy expenditure was significantly lower in competitive runners (152.6 ± 33.3 kJ) in comparison to recreational runners (200.6 ± 41.4 kJ) (P = 0.02) given similar amounts of external work performed in both groups (competitive runners = 65.6 ± 20.1 kJ, recreational runners = 68.8 ± 12.1 kJ) (P = 0.67). Index of mechanical efficiency was significantly different between competitive runners (43.2 ± 9.0%) and recreational runners (34.8 ± 5.3%) (P = 0.03). No significant differences were found in lower extremity stiffness (P = 0.64). Competitive distance runners can perform similar levels of external work with lower net energy expenditure and thus a higher index of mechanical efficiency during repetitive stretch-shortening cycles in comparison to recreational runners with similar values of lower extremity stiffness. This ability could possibly be due differences in muscle-tendon length changes, muscle pre-activation, cross-bridge potentiation and short-latency reflex responses as a result of training which should be considered for future investigation.

Mechanical efficiency and force­time curve variation during repetitive jumping in trained and untrained jumpers.

Mechanical efficiency (ME), the ratio between work performed and energy expenditure, is a useful criterion in determining the roles of stored elastic energy and chemically deduced energy contributing to concentric performance in stretch-shortening cycle movements. Increased force production during the eccentric phase has been shown to relate to optimal muscle-tendon unit (MTU) length change and thus optimization of usage of stored elastic energy. This phenomenon, as previously reported, is reflected by higher jump heights and ME. The purpose of this investigation was to determine if ME may be different between trained and untrained jumpers and thus be accounted for by variation in force production in the eccentric phase as a reflection of usage of stored elastic energy during various jump types. This investigation involved 9 trained (age 20.7 ± 3.2 years, height 178.6 ± 5.3 cm, body mass 79.0 ± 5.5 kg) and 7 untrained (age 21.43 ± 2.37 years, height 176.17 ± 10.89 cm, body mass 78.8 ± 12.5 kg) male jumpers. Trained subjects were Division I track and field athletes who compete in the horizontal or vertical jumping or running events. Force-time and displacement-time curves were obtained during jumping to determine jump height and to calculate work performed and to observe possible differences in force production in the eccentric phase. Respiratory gases with a metabolic cart were obtained during jumping to calculate energy expenditure. ME was calculated as the ratio between work performed and energy expenditure. The subjects completed four sessions involving 20 repetitions of countermovement jumps (CMJ) and drop jumps from 40 cm (DJ40), 60 cm (DJ60) and 80 cm (DJ80). The trained jumpers jumped significantly higher in the CMJ, DJ40, DJ60 and DJ80 conditions than their untrained counterparts (p ≤ 0.05). ME was significantly higher in the trained in comparison to the untrained jumpers during DJ40. The amount of negative work during all jump types was significantly greater in the trained jumpers. There was a significant correlation between negative work and ME in the trained jumpers (r = 0.82) but not in the untrained jumpers (r = 0.54). The present study indicates that trained jumpers jump higher and have greater ME, possibly as a result of increased for production in the eccentric phase as a reflection of optimal MTU length change and thus increased usage of storage of elastic energy.

Endotoxin releases a precursor to vasodilation from large veins in an NF-kappaB-dependent manner.

INTRODUCTION: Our previous studies have shown that when a segment of rat aorta was placed upstream and in series to a rat cremasteric isolated arteriole, endotoxin (ET) exposure produced significant vasodilatation. Without the aorta, no loss of tone was noted, indicating that a precursor, as of yet unidentified, was washed downstream, thereby inducing vasodilation. Prior treatment of the donor of either the aorta or the arteriole with pyrrolidine dithiocarbamate (PDTC), a potent NF-kappaB inhibitor, prevented the loss of tone. This suggests a role for NF-kappaB in the signaling pathway. The aim of this study was to determine if a large vein was also capable of releasing a similar factor in response to ET. MATERIALS AND METHODS: This project followed the same experimental design except that the upstream aortic segment was replaced by a segment of vena cava. Male Sprague-Dawley rats were given an intraperitoneal (ip) injection of PDTC (100 mg/kg) or a sham injection of saline. First-order cremasteric arterioles were isolated, cannulated, and pressurized. A segment of inferior vena cava was then placed in series with the microvascular preparation. Arterioles were allowed to equilibrate and achieve spontaneous myogenic tone in a bath of warm physiological buffer over 1 h (t = 0). Internal vessel diameters were measured with video calipers and the response to ET or continued infusion of buffer was measured over 2 h (t = 120). The control group (n = 8) received a sham injection and the vessels were exposed to buffer only. The ET group (n = 7) was exposed to ET only. The PDTC group (n = 5) received PDTC only. The PDTC/ET group (n = 6) received PDTC and was exposed to ET. RESULTS: After equilibration, spontaneous tone (measured as a percentage of maximal diameter) was similar in the four groups (t = 0). After 2 h (t = 120), the ET group had significantly less tone (30.1 +/- 3.6%; P < 0.05) than the control (44.8 +/- 2.6%), the PDTC group (43.0 +/- 1.3%), and the PDTC/ET group (49.4 +/- 3.0%). CONCLUSIONS: These results show that the vena cava is capable of releasing a factor leading to vasodilation in response to ET in a manner similar to the aorta. Produced by the veins, it will affect venous capacitance as well as contribute to the total amount in the plasma pool affecting the tone of the resistant arterioles. Thus, it appears that these large conducting vessels, regardless of origin, play a role in the deleterious effects during septic events.

PDTC and Mg132, inhibitors of NF-kappaB, block endotoxin induced vasodilation of isolated rat skeletal muscle arterioles.

NF-kappaB is a ubiquitous transcription factor that mediates the inflammatory response. Inhibition of NF-kappaB may be of potential therapeutic benefit in the treatment of septic shock. The antioxidant pyrrolidine dithiocarbamate (PDTC) has been shown in previous work to selectively inhibit NF-kappaB activation. Likewise, the proteasome inhibitor MG132 inhibits NF-kappaB formation and degradation of its inhibitor I-kappaB. The goal of this study was to determine if PDTC and MG-132 could inhibit resistance arteriole vasodilation in response to endotoxin and to determine PDTC's site of action in our isolated vessel preparation. Male Sprague-Dawley rats were given an intraperitoneal injection of PDTC, an intravenous injection of MG132, or a sham injection. First-order cremasteric arterioles were isolated, cannulated, and pressurized. A segment of thoracic aorta was then placed in series with the microvascular preparation. Vessels were allowed to achieve spontaneous myogenic tone in a bath of buffer over 1 h (t = 0). Internal vessel diameters were measured and the response to endotoxin (ET) or continued infusion of buffer was measured over 1 h (t = 60). Group 1 (n = 7) was a time-control group. Group 2 (n = 7) was exposed to ET only, Group 3 (n = 5) received PDTC and was exposed to ET, Group 4 (n = 5) received PDTC only, Group 5 (n = 4) received MG132 only, and Group 6 (n = 5) received MG132 and was exposed to ET. To determine the site of action of PDTC, a segment of aorta from an animal treated with PDTC was placed in series with a cremasteric arteriole from an animal receiving a sham injection. The preparation was then exposed to ET, and this is Group 7 (n = 4). Group 8 (n = 4) received ET and was composed of thoracic aorta from an animal receiving a sham injection and a cremasteric arteriole from a PDTC-treated animal. Spontaneous tone was similar in the eight groups at the end of the equilibration period (t = 0). After 1 h (t = 60), Group 2 (vessels exposed to ET only) had significantly less tone (26.1%+/-2.6%; P < 0.01) than Group 1 (39.0%+/-2.4%), Group 3 (39.3%+/-3.1%), Group 4 (41.2%+/-1.6%), Group 5 (39.2%+/-2.9%), Group 6 (41.0%+/-2.7%), Group 7 (45.1%+/-6.5%), and Group 8 (41.1%+/-4.5%). We conclude that PDTC and MG132, inhibitors of NF-kappaB, block ET-induced vasodilation in isolated rat skeletal muscle arterioles. PDTC has effects at both the level of the aortic segment as well as the resistance arteriole. Inhibitors of NF-kappaB may potentially be of therapeutic benefit in the treatment of septic shock.