Neuromuscular electrical stimulation during maximal voluntary contraction: a Delphi survey with expert consensus

PURPOSE

The use of electrical stimulation to assess voluntary activation of muscle/s is a popular method employed in numerous exercise science and health research settings. This Delphi study aimed to collate expert opinion and provide recommendations for best practice when using electrical stimulation during maximal voluntary contractions.

METHODS

A two-round Delphi study was undertaken with 30 experts who completed a 62-item questionnaire (Round 1) comprising of open- and closed-ended questions. Consensus was assumed if ≥ 70% of experts selected the same response; such questions were removed from the subsequent Round 2 questionnaire. Responses were also removed if they failed to meet a 15% threshold. Open-ended questions were analysed and converted into closed-ended questions for Round 2. It was assumed there was no clear consensus if a question failed to achieve a ≥ 70% response in Round 2.

RESULTS

A total of 16 out of 62 (25.8%) items reached consensus. Experts agreed that electrical stimulation provides a valid assessment of voluntary activation in specific circumstances, such as during maximal contraction, and this stimulation can be applied at either the muscle or the nerve. Experts recommended using doublet stimuli, self-adhesive electrodes, a familiarisation session, real-time visual or verbal feedback during the contraction, a minimum current increase of + 20% to ensure supramaximal stimulation, and manually triggering stimuli.

CONCLUSION

The results of this Delphi consensus study can help researchers make informed decisions when considering technical parameters when designing studies involving electrical stimulation for the assessment of voluntary activation.

Increased footwear comfort is associated with improved running economy - a systematic review and meta-analysis

Footwear with or without custom foot orthotics have the potential to improve comfort, but the link with running performance needs further investigation. We systematically reviewed the association of footwear comfort on running economy in recreational runners. Nine electronic databases were searched from inception to March 2020. Eligible studies investigated both direct outcome measures of running performance (e.g. running speed) and/or physiological measures (e.g. running economy (RE)) alongside comfort for each footwear condition tested. Methodological quality was assessed using the "Effective Public Health Practice Project" (EPHPP). RE during submaximal running was the most common physiological outcome reported in 4 of the 6 eligible studies. The absolute difference in RE between the most and least comfortable footwear condition was computed, and meta-analysis was conducted using a random effect model. The most comfortable footwear is associated with a reduction in oxygen consumption (MD: -2.06 mL.kg^-1.min^-1, 95%CI: -3.71, -0.42, P = 0.01) while running at a set submaximal speed. There was no significant heterogeneity (I² = 0%, P = 0.82). EPHPP quality assessment demonstrated weak quality of the studies, due to reporting bias and failing to disclose the psychometric properties of the outcome measures. It can be concluded with moderate certainty that improved RE in recreational athletes is associated with wearing more comfortable footwear compared to less comfortable footwear.HighlightsThis systematic review reports on the association of footwear comfort with running economy in recreational runners.Running economy during constant submaximal running is likely improved in recreational runners wearing more comfortable compared to less comfortable footwear.This finding is based on a meta-analysis, including four studies, showing a small but statistically significant decreased oxygen consumption at steady state speeds while wearing the most comfortable footwear.

How does multi-set high-load resistance exercise impact neuromuscular function in normoxia and hypoxia?

This study examined whether hypoxia during multi-set, high-load resistance exercise alters neuromuscular responses. Using a single-blinded (participants), randomised crossover design, eight resistance-trained males completed five sets of five repetitions of bench press at 80% of one repetition maximum in moderate normobaric hypoxia (inspiratory oxygen fraction = 0.145) and normoxia. Maximal isometric bench press trials were performed following the warm-up, after 10 min of altitude priming and 5 min post-session (outside, inside and outside the chamber, respectively). Force during pre-/post-session maximal voluntary isometric contractions and bar velocity during exercise sets were measured along with surface electromyographic (EMG) activity of the pectoralis major, anterior deltoid and lateral and medial triceps muscles. Two-way repeated measures ANOVA (condition×time) were used. A significant time effect (p = 0.048) was found for mean bar velocity, independent of condition (p = 0.423). During sets of the bench press exercise, surface EMG amplitude of all studied muscles remained unchanged (p > 0.187). During maximal isometric trials, there were no main effects of condition (p > 0.666) or time (p > 0.119), nor were there any significant condition×time interactions for peak or mean forces and surface EMG amplitudes (p > 0.297). Lower end-exercise blood oxygen saturation (90.9 ± 1.8 vs. 98.6 ± 0.6%; p < 0.001) and higher blood lactate concentration (5.8 ± 1.4 vs. 4.4 ± 1.6 mmol/L; p = 0.007) values occurred in hypoxia. Acute delivery of systemic normobaric hypoxia during multi-set, high-load resistance exercise increased metabolic stress. However, only subtle neuromuscular function adjustments occurred with and without hypoxic exposure either during maximal isometric bench press trials before versus after the session or during actual exercise sets.

Sensitivity of the Inhomogeneous Magnetization Transfer Imaging Technique to Spinal Cord Damage in Multiple Sclerosis

BACKGROUND AND PURPOSE

The inhomogeneous magnetization transfer technique has demonstrated high specificity for myelin, and has shown sensitivity to multiple sclerosis-related impairment in brain tissue. Our aim was to investigate its sensitivity to spinal cord impairment in MS relative to more established MR imaging techniques (volumetry, magnetization transfer, DTI).

MATERIALS AND METHODS

Anatomic images covering the cervical spinal cord from the C1 to C6 levels and DTI, magnetization transfer/inhomogeneous magnetization transfer images at the C2/C5 levels were acquired in 19 patients with MS and 19 paired healthy controls. Anatomic images were segmented in spinal cord GM and WM, both manually and using the AMU₄₀ atlases. MS lesions were manually delineated. MR metrics were analyzed within normal-appearing and lesion regions in anterolateral and posterolateral WM and compared using Wilcoxon rank tests and z scores. Correlations between MR metrics and clinical scores in patients with MS were evaluated using the Spearman rank correlation.

RESULTS

AMU₄₀-based C1-to-C6 GM/WM automatic segmentations in patients with MS were evaluated relative to manual delineation. Mean Dice coefficients were 0.75/0.89, respectively. All MR metrics (WM/GM cross-sectional areas, normal-appearing and lesion diffusivities, and magnetization transfer/inhomogeneous magnetization transfer ratios) were observed altered in patients compared with controls (P < .05). Additionally, the absolute inhomogeneous magnetization transfer ratio z scores were significantly higher than those of the other MR metrics (P < .0001), suggesting a higher inhomogeneous magnetization transfer sensitivity toward spinal cord impairment in MS. Significant correlations with the Expanded Disability Status Scale (ρ = -0.73/P = .02, ρ = -0.81/P = .004) and the total Medical Research Council scale (ρ = 0.80/P = .009, ρ = -0.74/P = .02) were observed for inhomogeneous magnetization transfer and magnetization transfer ratio z scores, respectively, in normal-appearing WM regions, while weaker and nonsignificant correlations were obtained for DTI metrics.

CONCLUSIONS

With inhomogeneous magnetization transfer being highly sensitive to spinal cord damage in MS compared with conventional magnetization transfer and DTI, it could generate great clinical interest for longitudinal follow-up and potential remyelinating clinical trials. In line with other advanced myelin techniques with which it could be compared, it opens perspectives for multicentric investigations.

Psycho-physiological responses to perceptually-regulated interval runs in hypoxia and normoxia

We investigated whether perceptually-regulated high-intensity intervals in hypoxia are associated with slower running velocities versus normoxia, when physiological responses and exercise-related sensations remain the same. Nineteen trained runners (33.4 ± 9.1 years) completed a high-intensity interval running protocol (4 × 4-min intervals at a clamped perceived rating exertion of 16 on the 6-20 Borg scale, 3-min passive recoveries) in either hypoxic (HYP; FiO₂ 15.0%) or normoxic (NOR; FiO₂ 20.9%) conditions. Participants adjusted to a progressively slower running velocity from interval 1-4 (-7.0%), and more so in HYP vs. NOR for intervals 2, 3 and 4 (-4.6%, -6.4% and - 7.9%, respectively; p < .01). Heart rate increased from interval 1-4 (+4.8%; p < .01), independent of condition. Arterial oxygen saturation was lower in HYP vs. NOR (86.0% vs. 94.8%; p < .01). Oxyhemoglobin (-23.7%) and total hemoglobin (-77.0%) decreased, whilst deoxyhemoglobin increased (+44.9%) from interval 1-4 (p < .01), independent of condition. Perceived recovery (-41.6%) and motivation (-21.8%) were progressively lower from interval 1-4, and more so in HYP vs. NOR for intervals 2, 3 and 4 (recovery: -8.8%, -24.2% and - 29.3%; motivation: -5.3%, -20.3% and - 22.4%, respectively; p < .01). Perceived breathlessness (+18.6%), limb discomfort (+44.0%) and pleasure (-32.2%) changed from interval 1-4, with significant differences (+21.8%, +11.3% and - 31.3%, respectively) between HYP and NOR (p < .01). Slower interval running velocities in hypoxia achieve similar heart rate and muscle oxygenation responses to those observed in normoxia when perceptually-regulated, yet at the expense of less favourable exercise-related sensations.

Evaluation of the Sensitivity of Inhomogeneous Magnetization Transfer (ihMT) MRI for Multiple Sclerosis

BACKGROUND AND PURPOSE

Inhomogeneous magnetization transfer is a new endogenous MR imaging contrast mechanism that has demonstrated high specificity for myelin. Here, we tested the hypothesis that inhomogeneous magnetization transfer is sensitive to pathology in a population of patients with relapsing-remitting MS in a way that both differs from and complements conventional magnetization transfer.

MATERIALS AND METHODS

Twenty-five patients with relapsing-remitting MS and 20 healthy volunteers were enrolled in a prospective MR imaging research study, whose protocol included anatomic imaging, standard magnetization transfer, and inhomogeneous magnetization transfer imaging. Magnetization transfer and inhomogeneous magnetization transfer ratios measured in normal-appearing brain tissue and in MS lesions of patients were compared with values measured in control subjects. The potential association of inhomogeneous magnetization transfer ratio variations with the clinical scores (Expanded Disability Status Scale) of patients was further evaluated.

RESULTS

The magnetization transfer ratio and inhomogeneous magnetization transfer ratio measured in the thalami and frontal, occipital, and temporal WM of patients with MS were lower compared with those of controls (P < .05). The mean inhomogeneous magnetization transfer ratio measured in lesions was lower than that in normal-appearing WM (P < .05). Significant (P < .05) negative correlations were found between the clinical scores and inhomogeneous magnetization transfer ratio measured in normal-appearing WM structures. Weaker nonsignificant correlation trends were found for the magnetization transfer ratio.

CONCLUSIONS

The sensitivity of the inhomogeneous magnetization transfer technique for MS was highlighted by the reduction in the inhomogeneous magnetization transfer ratio in MS lesions and in normal-appearing WM of patients compared with controls. Stronger correlations with the Expanded Disability Status Scale score were obtained with the inhomogeneous magnetization transfer ratio compared with the standard magnetization transfer ratio, which may be explained by the higher specificity of inhomogeneous magnetization transfer for myelin.

Adaptations in muscle oxidative capacity, fiber size, and oxygen supply capacity after repeated-sprint training in hypoxia combined with chronic hypoxic exposure

In this study, we investigate adaptations in muscle oxidative capacity, fiber size and oxygen supply capacity in team-sport athletes after six repeated-sprint sessions in normobaric hypoxia or normoxia combined with 14 days of chronic normobaric hypoxic exposure. Lowland elite field hockey players resided at simulated altitude (≥14 h/day at 2,800-3,000 m) and performed regular training plus six repeated-sprint sessions in normobaric hypoxia (3,000 m; LHTLH; n = 6) or normoxia (0 m; LHTL; n = 6) or lived at sea level with regular training only (LLTL; n = 6). Muscle biopsies were obtained from the m. vastus lateralis before (pre), immediately after (post-1), and 3 wk after the intervention (post-2). Changes over time between groups were compared, including likelihood of the effect size (ES). Succinate dehydrogenase activity in LHTLH largely increased from pre to post-1 (~35%), likely more than LHTL and LLTL (ESs = large-very large), and remained elevated in LHTLH at post-2 (~12%) vs. LHTL (ESs = moderate-large). Fiber cross-sectional area remained fairly similar in LHTLH from pre to post-1 and post-2 but was increased at post-1 and post-2 in LHTL and LLTL (ES = moderate-large). A unique observation was that LHTLH and LHTL, but not LLTL, improved their combination of fiber size and oxidative capacity. Small-to-moderate differences in oxygen supply capacity (i.e., myoglobin and capillarization) were observed between groups. In conclusion, elite team-sport athletes substantially increased their skeletal muscle oxidative capacity, while maintaining fiber size, after only 14 days of chronic hypoxic residence combined with six repeated-sprint training sessions in hypoxia. NEW & NOTEWORTHY Our novel findings show that elite team-sport athletes were able to substantially increase the skeletal muscle oxidative capacity in type I and II fibers (+37 and +32%, respectively), while maintaining fiber size after only 14 days of chronic hypoxic residence combined with six repeated-sprint sessions in hypoxia. This increase in oxidative capacity was superior to groups performing chronic hypoxic residence with repeated sprints in normoxia and residence at sea level with regular training only.

Repeated maximal-intensity hypoxic exercise superimposed to hypoxic residence boosts skeletal muscle transcriptional responses in elite team-sport athletes

AIM

To determine whether repeated maximal-intensity hypoxic exercise induces larger beneficial adaptations on the hypoxia-inducible factor-1α pathway and its target genes than similar normoxic exercise, when combined with chronic hypoxic exposure.

METHODS

Lowland elite male team-sport athletes underwent 14 days of passive normobaric hypoxic exposure [≥14 h·day^-1 at inspired oxygen fraction (F_i O₂ ) 14.5-14.2%] with the addition of six maximal-intensity exercise sessions either in normobaric hypoxia (F_i O₂ ~14.2%; LHTLH; n = 9) or in normoxia (F_i O₂ 20.9%; LHTL; n = 11). A group living in normoxia with no additional maximal-intensity exercise (LLTL; n = 10) served as control. Before (Pre), immediately after (Post-1) and 3 weeks after (Post-2) the intervention, muscle biopsies were obtained from the vastus lateralis.

RESULTS

Hypoxia-inducible factor-1α subunit, vascular endothelial growth factor, myoglobin, peroxisome proliferator-activated receptor-gamma coactivator 1-α and mitochondrial transcription factor A mRNA levels increased at Post-1 (all P ≤ 0.05) in LHTLH, but not in LHTL or LLTL, and returned near baseline levels at Post-2. The protein expression of citrate synthase increased in LHTLH (P < 0.001 and P < 0.01 at Post-1 and Post-2, respectively) and LLTL (P < 0.01 and P < 0.05 at Post-1 and Post-2, respectively), whereas it decreased in LHTL at Post-1 and Post-2 (both P < 0.001).

CONCLUSION

Combined with residence in normobaric hypoxia, repeated maximal-intensity hypoxic exercise induces short-term post-intervention beneficial changes in muscle transcriptional factors that are of larger magnitude (or not observed) than with similar normoxic exercise. The decay of molecular adaptations was relatively fast, with most of benefits already absent 3 weeks post-intervention.

Normobaric hypoxic conditioning to maximize weight loss and ameliorate cardio-metabolic health in obese populations: a systematic review

Normobaric hypoxic conditioning (HC) is defined as exposure to systemic and/or local hypoxia at rest (passive) or combined with exercise training (active). HC has been previously used by healthy and athletic populations to enhance their physical capacity and improve performance in the lead up to competition. Recently, HC has also been applied acutely (single exposure) and chronically (repeated exposure over several weeks) to overweight and obese populations with the intention of managing and potentially increasing cardio-metabolic health and weight loss. At present, it is unclear what the cardio-metabolic health and weight loss responses of obese populations are in response to passive and active HC. Exploration of potential benefits of exposure to both passive and active HC may provide pivotal findings for improving health and well being in these individuals. A systematic literature search for articles published between 2000 and 2017 was carried out. Studies investigating the effects of normobaric HC as a novel therapeutic approach to elicit improvements in the cardio-metabolic health and weight loss of obese populations were included. Studies investigated passive (n = 7; 5 animals, 2 humans), active (n = 4; all humans) and a combination of passive and active (n = 4; 3 animals, 1 human) HC to an inspired oxygen fraction ([Formula: see text]) between 4.8 and 15.0%, ranging between a single session and daily sessions per week, lasting from 5 days up to 8 mo. Passive HC led to reduced insulin concentrations (-37 to -22%) in obese animals and increased energy expenditure (+12 to +16%) in obese humans, whereas active HC lead to reductions in body weight (-4 to -2%) in obese animals and humans, and blood pressure (-8 to -3%) in obese humans compared with a matched workload in normoxic conditions. Inconclusive findings, however, exist in determining the impact of acute and chronic HC on markers such as triglycerides, cholesterol levels, and fitness capacity. Importantly, most of the studies that included animal models involved exposure to severe levels of hypoxia ([Formula: see text] = 5.0%; simulated altitude >10,000 m) that are not suitable for human populations. Overall, normobaric HC demonstrated observable positive findings in relation to insulin and energy expenditure (passive), and body weight and blood pressure (active), which may improve the cardio-metabolic health and body weight management of obese populations. However, further evidence on responses of circulating biomarkers to both passive and active HC in humans is warranted.

Plantar flexor neuromuscular adjustments following match-play football in hot and cool conditions

We assessed neuromuscular fatigue and recovery of the plantar flexors after playing football with or without severe heat stress. Neuromuscular characteristics of the plantar flexors were assessed in 17 male players at baseline and ∼30 min, 24, and 48 h after two 90-min football matches in temperate (∼20 °C and 55% rH) and hot (∼43 °C and 20% rH) environments. Measurements included maximal voluntary strength, muscle activation, twitch contractile properties, and rate of torque development and soleus EMG (i.e., root mean square activity) rise from 0 to 30, -50, -100, and -200 ms during maximal isometric contractions for plantar flexors. Voluntary activation and peak twitch torque were equally reduced (-1.5% and -16.5%, respectively; P < 0.05) post-matches relative to baseline in both conditions, the latter persisting for at least 48 h, whereas strength losses (∼5%) were not significant. Absolute explosive force production declined (P < 0.05) 30 ms after contraction onset independently of condition, with no change at any other epochs. Globally, normalized rate of force development and soleus EMG activity rise values remained unchanged. In football, match-induced alterations in maximal and rapid torque production capacities of the plantar flexors are moderate and do not differ after competing in temperate and hot environments.

Consensus recommendations on training and competing in the heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimise performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimise performance is to heat acclimatise. Heat acclimatisation should comprise repeated exercise-heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimise dehydration during exercise. Following the development of commercial cooling systems (eg, cooling-vest), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organisers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimising the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events, for hydration and body cooling opportunities, when competitions are held in the heat.

Changes in running mechanics and spring-mass behaviour during a 5-km time trial

Research into the biomechanical manifestation of fatigue during exhaustive runs is increasingly popular but additional understanding of the adaptation of the spring-mass behaviour during the course of strenuous, self-paced exercises continues to be a challenge in order to develop optimized training and injury prevention programs. This study investigated continuous changes in running mechanics and spring-mass behaviour during a 5-km run. 12 competitive triathletes performed a 5-km running time trial (mean performance: ̴17 min 30 s) on a 200 m indoor track. Vertical and anterior-posterior ground reaction forces were measured every 200 m by a 5-m long force platform system, and used to determine spring-mass model characteristics. After a fast start, running velocity progressively decreased (- 11.6%; P<0.001) in the middle part of the race before an end spurt in the final 400-600 m. Stride length (- 7.4%; P<0.001) and frequency (- 4.1%; P=0.001) decreased over the 25 laps, while contact time (+ 8.9%; P<0.001) and total stride duration (+ 4.1%; P<0.001) progressively lengthened. Peak vertical forces (- 2.0%; P<0.01) and leg compression (- 4.3%; P<0.05), but not centre of mass vertical displacement (+ 3.2%; P>0.05), decreased with time. As a result, vertical stiffness decreased (- 6.0%; P<0.001) during the run, whereas leg stiffness changes were not significant (+ 1.3%; P>0.05). Spring-mass behaviour progressively changes during a 5-km time trial towards deteriorated vertical stiffness, which alters impact and force production characteristics.

Effects of the playing surface on plantar pressures and potential injuries in tennis

OBJECTIVES

To examine the influence of different playing surfaces on in-shoe loading patterns during tennis-specific movements.

METHODS

Ten experienced male players performed two types of tennis-specific displacements (serve and volley (SV) and baseline play (BA)) on two different playing surfaces; eg, clay vs Greenset. Maximum and mean force and pressure, contact time, contact area and relative load were recorded by an insole with 99 sensors (X-Pedar system) divided into 9 areas.

RESULTS

Regarding the whole foot, mean (SD) force (SV: 615 (91) vs 724 (151) N; -12.4%, p<0.05 and BA: 614 (73) vs 717 (133) N; -11.6%, p<0.05) was lower on clay than on Greenset, whereas contact time was longer (SV: 299 (113) vs 270 (148) ms; +16.5%, NS and BA: 354 (72) vs 272 (60) ms; +30.3%, p<0.001). Greenset induced higher loading in the hallux (SV: +15.3%, p<0.05 and BA: +11.4%, not significant) and lesser toes areas (SV: +12.6%, p<0.05 and BA: +18.0%, p<0.01). In contrast, the relative load on the medial (SV: +27.4%, p<0.05 and BA: +16.1%, p = 0.06) and lateral midfoot (SV: +23.3%, p<0.05 and BA: +28.3%, p<0.01) was higher on clay.

CONCLUSIONS

This study demonstrates that playing surface affects plantar loading in tennis: Greenset induced higher loading in the hallux (SV: +15.3%, p<0.05 and BA: +11.4%, NS) and lesser toes areas (SV: +12.6%, p<0.05 and BA: +18.0%, p<0.01) but lower relative load on the medial (SV: -27.4%, p<0.05 and BA: -16.1%, p = 0.06) and lateral midfoot (SV: -23.3%, p<0.05 and BA: -28.3%, p<0.01) than clay.

Failed excitability of spinal motoneurons induced by prolonged running exercise

The main purpose of this study was to investigate the modulations in H-reflex and V-wave responses (spinal loop properties) induced by prolonged locomotion activities. The second purpose was to compare the development of central fatigue between continuous and intermittent running modes. Eleven males randomly performed two 90-min running exercises either continuously (CONT, first ventilatory threshold) or intermittently (INT, 150 s at a velocity 20% higher than that during CONT/30 s of recovery). Neuromuscular tests of the plantar flexors [including M-wave and H-reflex at rest and M-wave and V-wave during maximal voluntary contraction (MVC)] were performed before and 5 and 30 min after the running exercises. During MVC, the torque significantly decreased (P < 0.05) from preexercise to 5 and 30 min postexercise (-11 and -9%, respectively), as did the RMS/M ratio (-11 and -13%, respectively) and the V/M ratio (-19 and -37%, respectively) for the soleus muscle. At rest, the H/M ratio also decreased significantly (P < 0.001) from preexercise to 5 and 30 min postexercise (-61 and -55%, respectively). Last, no difference in the alteration of spinal loop properties was noted between CONT and INT. In conclusion, the results regarding H-reflex and V-wave suggest for the first time a modulation in spinal loop properties after prolonged running.

Specific incremental field test for aerobic fitness in tennis

OBJECTIVES

To compare metabolic and cardiorespiratory responses between subjects undergoing incremental treadmill (non-specific) and tennis field based (sport specific) tests.

METHODS

Nine junior competitive tennis players randomly performed two incremental protocols to exhaustion: a treadmill test (TT) and a tennis specific fitness test (FT). The FT consisted of repeated displacements replicating the game of tennis at increasing speed on a court. In both tests, ventilatory variables and heart rate (HR) were determined at the ventilatory threshold (VT), respiratory compensation point (RCP), and maximal loads (max). Blood lactate concentration was determined at the point of volitional fatigue.

RESULTS

Percentage (mean (SD)) maximal HR (83.6 (5.1) v 83.0 (2.8) and 92.1 (2.1) v 92.3 (2.1)%, respectively) and percentage maximal oxygen uptake (VO2max) (69.4 (8.1) v 73.5 (6.1) and 84.4 (6.5) v 85.5 (8.7)%, respectively) at the VT and RCP were not different between the FT and TT subjects, whereas VO2max was higher in the FT than in the TT (63.8 (3.0) v 58.9 (5.3) ml/min/kg; p<0.05). Blood lactate concentration (10.7 (3.0) v 10.6 (4.3) mmol/l) did not differ between the TT and FT.

CONCLUSIONS

Although cardiorespiratory variables were not different at submaximal intensities between the two tests, VO2max values derived from laboratory measurements were underestimated. Using field testing in addition to treadmill testing provides a better measurement of a player's individual fitness level and may be routinely used to accurately prescribe appropriate aerobic exercise training.

Changes in exercise characteristics, maximal voluntary contraction, and explosive strength during prolonged tennis playing

OBJECTIVES

To examine changes in exercise characteristics, maximal voluntary contraction, and explosive strength during prolonged tennis playing.

METHODS

Maximal isometric voluntary contraction (MVC), leg stiffness (hopping), and peak power in squat (SJ) and countermovement (CMJ) jumps were measured before, every 30 minutes during, and 30 minutes after a three hour tennis match in 12 well trained players. Heart rate (HR), the effective playing time (EPT), rating of perceived exertion (RPE), and muscle soreness of knee extensors were also measured.

RESULTS

Decreases in MVC (-9%; p < 0.05) and leg stiffness (-9%; p = 0.17) were observed after the match and were significantly correlated (r = 0.66; p = 0.05). Peak power in SJ and CMJ tests was maintained during the match but was lower (p < 0.001) 30 minutes after. Average HR and EPT were 144 (8) beats/min and 21 (4)% respectively. A strong correlation was found between EPT and HR (r = 0.93; p < 0.05). RPE and muscle soreness increased linearly during the exercise and were significantly correlated (r = 0.99; p < 0.001).

CONCLUSIONS

Progressive reductions in maximal voluntary strength and leg stiffness highly correlated with increases in perceived exertion and muscle soreness were observed throughout a three hour tennis match, whereas explosive strength was maintained and decreased only after the match. These alterations may result in less efficient on-court movement and stroke production. They are, however, lower than those reported during continuous exercise of the same duration. The intermittent pattern of tennis and the numerous stretch-shortening cycle movements partly explain these results.

Specific incremental test in elite squash players

OBJECTIVES

To compare cardiorespiratory responses between incremental treadmill (non-specific) and field (sport specific) tests in elite squash players.

METHODS

Seven elite players (ranked 1 to 25 in their national federation including the World number 1) randomly performed an incremental treadmill test (TT) and a squash specific graded test (ST) to exhaustion. The ST consisted of repeated displacements replicating the game of squash, at increasing speed on the court. In both tests, ventilatory variables and heart rate were determined at the ventilatory threshold, respiratory compensation point, and maximal loads (max).

RESULTS

Heart rate and percentage maximal oxygen uptake (VO2MAX) at the ventilatory threshold and respiratory compensation point were not different between the ST and TT, whereas VO2MAX was higher in the ST than in the TT (63.6 (3.0) v 54.9 (2.5) ml/kg/min; p < 0.001). Time to exhaustion was not different between the ST and TT (1056 (180) v 962 (71) seconds) but correlated with the ranking of the players only in the ST (r = -0.96, p < 0.001).

CONCLUSIONS

VO2MAX values derived from laboratory testing were not relevant for accurately estimating fitness in elite squash players. So the ST may be used as an additional test for determination of training intensity. Improved training advice for prescribing aerobic exercise or perfecting stroke technique may result from these results.

[Vitamin D and pregnancy: value of a single dose in the third trimester. Comparative study of 100 cases]

A comparative study (100 treated subjects, 100 controls) was carried out at the Centre Hospitalier at Meaux during the winter of 1984-85 in which pregnant women were given single doses of vitamin D to be taken at the seventh month of pregnancy. The results obtained for neonatal blood calcium levels clearly demonstrated the value of vitamin D supplements in pregnant women. This study was original in that a single dose of vitamin D was provided; this led to almost perfect therapeutic observance (99%).

[Studies of immunological status, following autologous bone marrow transplantation in man (author's transl)]

Following transplant, circulating immunoglobulin levels fell moderately and remained depressed less than 2 months for IgG, and for variable and longer periods of time for IgM and IgA. Repeated quantitative determinations of antibodies against multiple antigens did not show any decrease in the pretransplant levels. Indeed some patients developed herpes and cytomegalovirus infections to which they responded by a sharp increase in antibody titers. In 2 cases, a primary immunization was demonstrated (against CMV and BK virus) with increasing levels of IgM and IgG antibodies. Lymphocyte counts in peripheral blood returned to 500 mm# between day 10 and 29 (median day 18) and to pretransplant values within 6 weeks. Non specific stimulation of lymphocytes by mitogens in the immediate post-transplant period showed a decreased response to PHA and Con A, whereas the responses to pokeweek mitogens and alloantigens were only slightly diminished. The degree of the responses was related to the dose of cryopreserved marrow infused. We conclude that:--although the minimum dose for autologous bone marrow transplantation in man is around 0,5 10(8) nucleated bone marrow cells/Kg, much higher doses should be used to ensure faster and better restoration of immune reactivity.--The similarity of the immunological dysfunction following autologous and allogeneous bone marrow transplantation suggest that, in the immediate post-transplant period, the role of GVHD in cellular immunity depression may be minimal.

[Changes in anti-tetanus antibodies under sero-toxoid therapy. Study in 50 patients with tetanus]

A study concerning changes in anti-tetanus antibody (ATA) levels in 50 patients with tetanus following the injection of antitetanic serum of equine origin and of toxoid, the first dose of the latter being given 24 hours after the administration of serum and the others at intervals of 5 to 7, 15 and 30 days. Repeated estimation of ATA demonstrated, regardless of the toxoid dose protocol adopted, that levels did not reach 0.1 IU/ml on the 30th day and that they only rose late. By contrast, after a booster, the increase was the same as that seen in subjects who had not acquired tetanus. The various factors which may underly defective active immunisation during the acute phase of tetanus are discussed. Heterologue serum therapy, which has been held responsible, cannot be considered to be a responsible factor since patients who did not receive serum behaved in exactly the same way as those who had. By virtue of this "gap" in the acquisition of immunity, the use of heterologue serum is recommended to neutralise any remaining circulating toxin as rapidly as possible.