Reliability of the assessment of peripheral muscle fatigue induced by high-intensity intermittent exercise

AIM

Reliability of the assessment of peripheral fatigue induced in knee extensors by high-intensity intermittent running exercise (HIE) was established in ten amateur soccer players (age: 18±1, height: 178±5 cm, weight: 68±8 kg).

METHODS

Transcutaneous electrical stimulations before and after HIE determined muscle contractile properties on three separate occasions (T1, T2 and T3), each separated by 7 days.

RESULTS

No significant differences were noted for any of the parameters measured (P=0.101). The ICC values for peak torque (PT) varied from moderate to high, with the exception of PT at 10-Hz calculated comparing T2 vs. T1 (range PRE=0.78-0.92; POST=0.76-0.97). The ICC derived from PT percentage decrements data were all low, with the exception of PT decrements at 1 Hz calculated comparing T3 vs. T2 (ICC=0.85, moderate). The TE for all contractile parameters obtained using 1-Hz and 100-Hz electrical stimulations were below 10%, including some that demonstrated a TE lower than 5%. Muscle contractile properties determined using 10-Hz stimulations showed a higher level of TE (range: 3.2-15.1%). Similar results were obtained for maximal rate of torque development and torque relaxation.

CONCLUSION

From the results of this study it can be concluded that muscle contractile properties express a good level of reliability in baseline and postexercise measures following familiarization.

Accuracy of GPS devices for measuring high-intensity running in field-based team sports

We compared the accuracy of 2 GPS systems with different sampling rates for the determination of distances covered at high-speed and metabolic power derived from a combination of running speed and acceleration. 8 participants performed 56 bouts of shuttle intermittent running wearing 2 portable GPS devices (SPI-Pro, GPS-5 Hz and MinimaxX, GPS-10 Hz). The GPS systems were compared with a radar system as a criterion measure. The variables investigated were: total distance (TD), high-speed distance (HSR>4.17 m·s(-1)), very high-speed distance (VHSR>5.56 m·s(-1)), mean power (Pmean), high metabolic power (HMP>20 W·kg(-1)) and very high metabolic power (VHMP>25 W·kg(-1)). GPS-5 Hz had low error for TD (2.8%) and Pmean (4.5%), while the errors for the other variables ranged from moderate to high (7.5-23.2%). GPS-10 Hz demonstrated a low error for TD (1.9%), HSR (4.7%), Pmean (2.4%) and HMP (4.5%), whereas the errors for VHSR (10.5%) and VHMP (6.2%) were moderate. In general, GPS accuracy increased with a higher sampling rate, but decreased with increasing speed of movement. Both systems could be used for calculating TD and Pmean, but they cannot be used interchangeably. Only GPS-10 Hz demonstrated a sufficient level of accuracy for quantifying distance covered at higher speeds or time spent at very high power.

Physiological and anthropometric characteristics of junior cyclists of different specialties and performance levels

This study analyzes the anthropometric and physiological characteristics of junior cyclists within different cycling specialties and different performance levels. One hundred and thirty-two junior riders (16.8 ± 0.6 years, 177 ± 6 cm, 66.3 ± 6.7 kg) were tested for anthropometric, aerobic and anaerobic parameters. Cyclists were classified within specialties [uphill (UH) flat terrain (FT) all terrain (AT) and sprint (SP)] and performance levels, based on a seasonal ranking [low level (LL) medium level (ML) and high level (HL)]. The results of the two-way analysis of variance showed that FT and SP have greater body dimensions than UH and AT (P<0.001). Concerning the relative aerobic parameters, AT and UH have higher values (P<0.001) than FT and SP [maximal oxygen uptake (VO(2max) ): 69.4 ± 3.6, 67.5 ± 5.0, 62.8 ± 4.5 and 61.9 ± 4.1 mL/kg/min, respectively] while absolute parameters resulted higher for FT and AT (P≤0.008). The relative power produced in the 5 s test was higher (P<0.001) for AT and SP than FT and UH (16.7 ± 1.1, 16.6 ± 0.6, 14.9 ± 1.7 and 14.4 ± 1.7 W/kg, respectively). Concerning the performance level, only the age and the aerobic parameters resulted differently within levels (VO(2max) : HL=67.3 ± 4.9, ML=65.5 ± 5.1 and LL=63.3 ± 5.2 mL/kg/min), with the highest values for HL (P≤0.007). In conclusion, juniors are specialized in the same way as professional cyclists and the aerobic characteristics are confirmed as significant in the performance level assessment.

Sprint vs. interval training in football

The aim of this study was to compare the effects of high-intensity aerobic interval and repeated-sprint ability (RSA) training on aerobic and anaerobic physiological variables in male football players. Forty-two participants were randomly assigned to either the interval training group (ITG, 4 x 4 min running at 90 - 95 % of HRmax; n = 21) or repeated-sprint training group (RSG, 3 x 6 maximal shuttle sprints of 40 m; n = 21). The following outcomes were measured at baseline and after 7 weeks of training: maximum oxygen uptake, respiratory compensation point, football-specific endurance (Yo-Yo Intermittent Recovery Test, YYIRT), 10-m sprint time, jump height and power, and RSA. Significant group x time interaction was found for YYIRT (p = 0.003) with RSG showing greater improvement (from 1917 +/- 439 to 2455 +/- 488 m) than ITG (from 1846 +/- 329 to 2077 +/- 300 m). Similarly, a significant interaction was found in RSA mean time (p = 0.006) with only the RSG group showing an improvement after training (from 7.53 +/- 0.21 to 7.37 +/- 0.17 s). No other group x time interactions were found. Significant pre-post changes were found for absolute and relative maximum oxygen uptake and respiratory compensation point (p < 0.05). These findings suggest that the RSA training protocol used in this study can be an effective training strategy for inducing aerobic and football-specific training adaptations.

Variation in Top Level Soccer Match Performance

This study examined the influence of the opposing team, seasonal variations and the influence of first half activity on match performance in top-level soccer players. Physical performance measures were collected using the ProZone match analysis system from 20 professional soccer players from the same team and their opponents (n = 188) during a season. Match activities (standing, walking, jogging, running, high-speed running and sprinting), distances (total distance [TD], high-intensity running [HIR] and very high-intensity running [VHIR]) and other measures including involvement with the ball and peak running speed were collected. The influence of opponent team, the level of opposition, first half physical activities on second half activities, and playing position were analysed. The main finding was that TD (r = 0.62, p < 0.05), HIR (r = 0.51, p < 0.05), and VHIR (r = 0.65, p < 0.05) of the reference team was influenced by the activity profile of the opponent teams. The TD and HIR was higher against Best opponent teams compared to Worst opponent teams (p < 0.05), and the TD, HIR and VHIR travelled in the first half significantly influenced the distances covered in the second half. TD, HIR and VHIR were greater at the end of the season. These results may be used to interpret meaningful changes in match performance in top level soccer.

Effect of plyometric training on sand versus grass on muscle soreness and jumping and sprinting ability in soccer players

OBJECTIVE

The lower impact on the musculoskeletal system induced by plyometric exercise on sand compared to a firm surface might be useful to reduce the stress of intensified training periods or during rehabilitation from injury. The aim of this study was to compare the effects of plyometric training on sand versus a grass surface on muscle soreness, vertical jump height and sprinting ability.

DESIGN

Parallel two-group, randomised, longitudinal (pretest-post-test) study.

METHODS

After random allocation, 18 soccer players completed 4 weeks of plyometric training on grass (grass group) and 19 players on sand (sand group). Before and after plyometric training, 10 m and 20 m sprint time, squat jump (SJ), countermovement jump (CMJ), and eccentric utilization ratio (CMJ/SJ) were determined. Muscle soreness was measured using a Likert scale.

RESULTS

No training surface x time interactions were found for sprint time (p>0.87), whereas a trend was found for SJ (p = 0.08), with both groups showing similar improvements (p<0.001). On the other hand, the grass group improved their CMJ (p = 0.033) and CMJ/SJ (p = 0.005) significantly (p<0.001) more than players in the sand group. In contrast, players in the sand group experienced less muscle soreness than those in the grass group (p<0.001).

CONCLUSIONS

Plyometric training on sand improved both jumping and sprinting ability and induced less muscle soreness. A grass surface seems to be superior in enhancing CMJ performance while the sand surface showed a greater improvement in SJ. Therefore, plyometric training on different surfaces may be associated with different training-induced effects on some neuromuscular factors related to the efficiency of the stretch-shortening cycle.

Physiological and performance effects of generic versus specific aerobic training in soccer players

The aim of this study was to compare the effects of specific (small-sided games) vs. generic (running) aerobic interval training on physical fitness and objective measures of match performance in soccer. Forty junior players were randomly assigned to either generic (n=20) or specific (n=20) interval training consisting of 4 bouts of 4 min at 90-95 % of maximum heart rate with 3 min active rest periods, completed twice a week. The following outcomes were measured at baseline (Pre), after 4 weeks of pre-season training (Mid), and after a further 8 weeks of training during the regular season (Post): maximum oxygen uptake, lactate threshold (Tlac), running economy at Tlac, a soccer-specific endurance test (Ekblom's circuit), and indices of physical performance during soccer matches (total distance and time spent standing, walking, and at low- and high-intensity running speed). Training load, as quantified by heart rate and rating of perceived exertion, was recorded during all training sessions and was similar between groups. There were significant improvements in aerobic fitness and match performance in both groups of soccer players, especially in response to the first 4 weeks of pre-season training. However, no significant differences between specific and generic aerobic interval training were found in any of the measured variables including soccer specific tests. The results of this study showed that both small-sided games and running are equally effective modes of aerobic interval training in junior soccer players.

Validity of simple field tests as indicators of match-related physical performance in top-level professional soccer players

The aim of this study was to examine the construct validity of selected field tests as indicators of match-related physical performance. During the competitive season, eighteen professional soccer players (age 26.2 +/- 4.5 yrs, mass 80.8 +/- 7.8 kg, and height 181.9 +/- 3.7 cm) completed an incremental running field test to exhaustion, a vertical-jump and a repeated-sprint ability (RSA) test. Match physical performance was quantified during official matches using a video-computerized, semi-automatic, match analysis image recognition system, (ProZone, Leeds, UK). The selected measures of match physical performance were: total distance covered (TD), high intensity running (HIR: > 14.4 km . h (-1)), very high intensity running (VHIR:> 19.8 km . h (-1)), sprinting (> 25.2 km . h (-1)) and top running speed. Significant correlations were found between peak speed reached during the incremental field test and TD (r = 0.58, R (2) = 0.34; p < 0.05), HIR (r = 0.65, R (2) = 0.42; p < 0.01) and VHIR (r = 0.64, R (2) = 0.41; p < 0.01). Significant correlations were also found between RSA mean time and VHIR (r = - 0.60, R (2) = 0.36; p < 0.01) and sprinting distance (r = - 0.65, R (2) = 0.42; p < 0.01). Significant differences were found between the best and worst group as defined by the median split technique for peak speed (TD = 12 011 +/- 747 m vs. 10 712 +/- 669, HIR = 3192 +/- 482 m vs. 2314 +/- 347 m, and VHIR = 1014 +/- 120 vs. 779 +/- 122 m, respectively; p < 0.05) and RSA mean time (VHIR = 974 +/- 162 m vs. 819 +/- 144 m, and sprinting = 235 +/- 56 vs. 164 +/- 58 m, respectively; p < 0.05). In conclusion, this study gives empirical support to the construct validity of RSA and incremental running tests as measures of match-related physical performance in top-level professional soccer players.

Prediction of time to exhaustion from blood lactate response during submaximal exercise in competitive cyclists

The aim of this investigation was to develop and validate a new method to predict time to exhaustion (pTE) from blood lactate variables measured during a submaximal non-exhaustive constant workload cycling test in professional cyclists. A multiple regression equation to estimate pTE from blood lactate variables measured within the first 10 min of a submaximal test and TE was determined in 40 competitive cyclists. Predicted TE reliability [individual coefficient of variation (CV)] was calculated in eight amateur cyclists who repeated the proposed test three times. Seasonal variations of pTE were monitored in 12 professional cyclists. Validity of pTE was determined by the known-group difference method in 49 professional cyclists. The prediction equation was: log(n)TE = 4.2067 - 0.8221(log(n) B) - 0.2519(log(n) C), where B is the lactate concentration at the 10th minute of the constant workload test and C is the lactate slope calculated between the 5th and 10th minute (adjusted r (2) =0.83, root mean square error in cross validation=23.1%). Predicted TE CV was 11.7%. The pTE obtained at the beginning of the season and the best and worst tests performed during the competitive season, resulted 162, 224 and 103% higher than the basic period test, respectively (P<0.05). Predicted TE was the only parameter discriminating elite from subelite professional cyclists. In conclusion, this study demonstrates that pTE is a valid and practical alternative to incremental tests and direct measures of endurance capacity requiring exhaustive efforts for the evaluation of competitive cyclists.

Correlations between physiological variables and performance in high level cross country off road cyclists

OBJECTIVES

To examine the relations between maximal and submaximal indices of aerobic fitness and off road cycling performance in a homogeneous group of high level mountain bikers.

METHODS

12 internationally competitive mountain bikers completed the study. Maximum oxygen uptake (Vo(2max)), peak power output (PPO), power output (PO), and oxygen uptake (Vo(2)) at first (VT) and second (RCT) ventilatory thresholds were measured in the laboratory, and correlated with race time during a cross country circuit race.

RESULTS

The only physiological indices of aerobic fitness correlated with off road cycling performance were PO and Vo(2) at RCT when normalised to body mass (r = -0.63 and r = -0.66, respectively; p<0.05). VT, Vo(2max), and PPO were not correlated to performance in this homogeneous group of high level mountain bikers.

CONCLUSIONS

The results of this study suggest that submaximal indices of aerobic fitness such as PO and Vo(2) at RCT are more important determinants of off road cycling performance than maximal indices such as PPO and Vo(2max). This study confirms the importance of body mass for mountain biking performance. As aerobic fitness explained only 40% of the variance, other physiological and technical factors should be investigated, as they may be important determinants of cross country performance among elite mountain bikers.

Cardiovascular responses to aerobic step dance sessions with and without appendicular overload

AIM

Several studies showed that exercise intensity during aerobic step dance can be modified varying stepping rate, bench height and manipulating body mass using hand held or adding loads to the torso. The aim of this study was to determine the cardiovascular responses during aerobic step dance using an overload strategy not yet investigated: appendicular overload.

METHODS

Ten healthy and moderately trained women (mean+/-SD: age 27+/-3.4 years, height 167.8+/-4.6 cm, body mass 55.7+/-4.7 kg, body mass index 19.8+/-1.6, VO2max44.4+/-6.1 mLxkg-1xmin-1) performed an incremental treadmill test to determine VO2peak, the VO2-heart rate (HR) and rating of perceived exertion (RPE)-HR relationships. Within 1 week from the laboratory test, the subjects performed two identical aerobic step dance routines: one using a track suit with loads placed in pockets close to the legs and arms and another without overload.

RESULTS

The appendicular overload (10% of body mass) significantly increased the exercise intensity from 84.5% to 89.8% of HRmax corresponding to 68.9% and 78.3% of VO2peak, respectively (P<0.01). Similarly, RPE increased from 12.1 to 15.7 (P<0.001). The estimated VO2 and the caloric expenditure rose from 30.3 to 34.7 mLxkg-1xmin-1 and from 251 to 288 kcal, respectively.

CONCLUSION

This study shows that the use of appendicular overload significantly increases the energy cost of aerobic step session similarly to other overload strategies already reported in the literature.