Neuromechanics of Middle-Distance Running Fatigue: A Key Role of the Plantarflexors?

PURPOSE

This study aimed to investigate the changes in lower limb kinematics, kinetics, and muscle activation during a high-intensity run to fatigue (HIRF).

METHODS

Eighteen male and female competitive middle-distance runners performed a HIRF on an instrumented treadmill at a constant but unsustainable middle-distance speed (~3 min) based on a preceding maximum oxygen uptake (V˙O2max) test. Three-dimensional kinematics and kinetics were collected and compared between the start, 33%, 67%, and the end of the HIRF. In addition, the activation of eight lower limb muscles of each leg was measured with surface EMG (sEMG).

RESULTS

Time to exhaustion was 181 ± 42 s. By the end of the HIRF (i.e., vs the start), ground contact time increased (+4.0%), whereas flight time (-3.2%), peak vertical ground reaction force (-6.1%), and vertical impulse (-4.1%) decreased (all P < 0.05), and joint angles at initial contact became more (dorsi)flexed (ankle, +1.9°; knee, +2.1°; hip, +3.6°; all P < 0.05). During stance, by the end of the HIRF: peak ankle plantarflexion moment decreased by 0.4 N·m·kg-1 (-9.0%), whereas peak knee extension moment increased by 0.24 N·m·kg-1 (+10.3%); similarly, positive ankle plantarflexion work decreased by 0.19 J·kg-1 (-13.9%), whereas positive knee extension work increased by 0.09 J·kg-1 (+33.3%; both P < 0.05) with no change in positive hip extension work. Hip extensor surface EMG amplitude increased during the late swing phase (+20.9-37.3%; P < 0.05).

CONCLUSION

Running at a constant middle-distance pace led primarily to the fatigue of the plantarflexors with a compensatory increase in positive work done at the knee. Improving the fatigue resistance of the plantarflexors might be beneficial for middle-distance running performance.

Eight weeks of intermittent hypoxic training improves submaximal physiological variables in highly trained runners

It is unclear whether intermittent hypoxic training (IHT) results in improvements in physiological variables associated with endurance running. Twelve highly trained runners (VO2peak 70.0 ± 3.5 ml·kg-1·min-1) performed incremental treadmill tests to exhaustion in normobaric normoxia and hypoxia (16.0% FIO2) to assess submaximal and maximal physiological variables and the limit of tolerance (T-Lim). Participants then completed 8 weeks of moderate to heavy intensity normoxic training (control [CONT]) or IHT (twice weekly 40 minutes runs, in combination with habitual training), in a single blinded manner, before repeating the treadmill tests. Submaximal heart rate decreased significantly more after IHT (-5 ± 5 b·min-1; p = 0.001) than after CONT ( -1 ± 5 b·min-1; p = 0.021). Changes in submaximal V[Combining Dot Above]O2 were significantly different between groups (p ≤ 0.05); decreasing in the IHT group in hypoxia (-2.6 ± 1.7 ml·kg-1·min-1; p = 0.001) and increasing in the CONT group in normoxia (+1.1 ± 2.1 ml·kg-1·min-1; p = 0.012). There were no VO2peak changes within either group, and while T-Lim improved post-IHT in hypoxia (p = 0.031), there were no significant differences between groups. Intermittent hypoxic training resulted in a degree of enhanced cardiovascular fitness that was evident during submaximal, but not maximal intensity exercise. These results suggest that moderate to heavy intensity IHT provides a mean of improving the capacity for submaximal exercise and may be useful for pre-acclimatization for subsequent exercise in hypoxia, but additional research is required to establish its efficacy for athletic performance at sea level.

Tracheobronchial malacia and stenosis in children in intensive care: bronchograms help to predict oucome

BACKGROUND

Severe tracheobronchial malacia and stenosis are important causes of morbidity and mortality in children in intensive care, but little is known about how best to diagnose these conditions or determine their prognosis.

METHODS

The records of all 62 children in whom one or both of these conditions had been diagnosed by contrast cinetracheobronchography in our intensive care unit in the period 1986-95 were studied.

RESULTS

Seventy four per cent of the 62 children had congenital heart disease; none was a preterm baby with airways disease associated with prolonged ventilation. Fifteen of the children had airway stenosis without malacia; three died because of the stenosis and two died from other causes. Twenty eight of the 47 children with malacia died; only eight children survived without developmental or respiratory handicap. All children needing ventilation for malacia for longer than 14 consecutive days died if their bronchogram showed moderate or severe malacia of either main bronchus (15 cases), or malacia of any severity of both bronchi (three additional cases); all children needing ventilation for malacia for longer than 21 consecutive days died if their bronchogram showed malacia of any severity of the trachea or a main bronchus (three additional cases). These findings were strongly associated with a fatal outcome (p<0.00005); they were present in 21 children (all of whom died) and absent in 26 (of whom seven died, six from non-respiratory causes). They had a positive predictive value for death of 100%, but the lower limit of the 95% confidence interval was 83.9% so up to 16% of patients meeting the criteria might survive.

CONCLUSION

In this series the findings on contrast cinetracheobronchography combined with the duration of ventilation provided a useful guide to the prognosis of children with tracheobronchomalacia. The information provided by bronchoscopy was less useful.

Spermatic-cord block improves analgesia for day-case testicular surgery

OBJECTIVE

To assess whether the use of a spermatic-cord block contributes any additional analgesia to that of a conventional analgesic regimen in day-case testicular surgery.

PATIENTS AND METHODS

In a randomized, double-blind controlled study, 48 patients undergoing day-case testicular surgery received general anaesthesia together with fentanyl and diclofenac for analgesia. In addition, 22 of these patients received 10 mL of 0.5% plain bupivacaine into the spermatic cord at the conclusion of surgery. Visual-analogue pain scores were recorded for each group over the following 24 h.

RESULTS

The visual-analogue pain scores were significantly lower in the immediate recovery period in patients receiving the spermatic-cord block.

CONCLUSION

The spermatic-cord block reduced discomfort in the immediate post-operative period in patients undergoing testicular surgery and the procedure should be encouraged to improve the quality of post-operative pain management in such procedures.

Hyperventilation-induced unconsciousness during labour

We report the development of unconsciousness caused by hyperventilation in an otherwise healthy woman in labour. Extradural analgesia resulted in restoration of full consciousness and normal respiratory state. The pathophysiology of hyperventilation and aspects of respiratory physiology in pregnancy are discussed.

Paradoxical cerebral embolism originating from thrombus in tumour veins as presenting manifestation of retroperitoneal liposarcoma

The coincidence of pulmonary and systemic emboli suggests paradoxical embolism. We present the case of a young man in whom a blood clot travelled from the veins in a retroperitoneal liposarcoma via a patent foramen ovalis to the systemic arterial circulation. Young patients with embolic disease but no obvious source of thrombus may have underlying neoplastic disease. Venous thrombosis is a frequent complication of neoplastic disease. Arterial embolism associated with neoplasm is, however, not widely recognised.