Repeated sprint ability (RSA) is an important fitness requirement for team sport athletes which can be improved through repeated sprint training (RST). Repeated shuttle sprints (RSS) seem to elicit greater physiological response in comparison to repeated sprints (RS) without change of direction. Whether this grater acute physiological response to RSS would result in greater training adaptations and whether these possible differences in training adaptations would lead to developing specific aspects of RSA needs to be investigated. PURPOSE: To determine the differences in training effects between RSS and RS training protocols. METHODS: Thirty nine male physical education students (19,6 ± 0,8 yrs) were divided into RS (n=20) and RSS (n=19) training groups and performed 18 training sessions in 6 weeks. RS training program consisted of 2-3 × 6-10 × 20m straight line RS, departing every 25 s, while RSS training consisted of RSS (10+10m) performed in the same training volume. Performance was assessed by 25 m sprint time (25 m), countermovement jump (CMJ), 20 m shuttle test (20 mST), incremental running test (VO2max) and time to exhaustion at vVO2max running test (tlim). For assessing repeated shuttle sprint ability (RSSA) and RSA subjects performed 6 repetitions of maximal 25m sprints with (2 × 12,5m) and without change of direction, departing every 25 s. The best sprint time (RSAb/RSSAb) and mean sprint time (RSAm/RSSAm) were calculated for both tests. A two way ANOVA with repeated measures and Pearson correlation coefficient were used for statistical analysis. RESULTS: RS and RSS group significantly (p≤0,05) improved in VO2max (5,1% vs 5%), 25 m (2,1% vs 1,7%), CMJ (4,5 vs 3,8%) and 20 mST (4,2% vs 4,2%), RSAb (3,3% vs 4,8%), RSAm (3,7% vs 4,6%), RSSAb (3,2% vs 4,6%) and RSSAm (2,6% vs 4,3%), but no significant differences in changes were observed. RSS training induced significantly greater improvements in tlim (-4,4% vs 15,3%). Correlation coefficient between RSAm and RSSAm decreased from 0,74 to 0,68. CONCLUSION: Both RS training protocols are equally efficient in improving VO2max, speed, jumping power, agility and both aspects of RSA. RSS training protocol induced greater adaptations in aerobic endurance. Mean sprinting time exists as a specific quality (r<0,71), so different RST protocols can induce specific changes in RSA.
Live fire-fighting activities place considerable cardiovascular and thermoregulatory strain on fire-fighters due to the combination of the metabolic heat generated by working muscles, the inability to dissipate heat, because of the protective clothing worn, and the considerable radiant heat they are exposed to. Whilst the instructors may not experience the high metabolic demands associated with the fire-fighting activity itself they are often exposed to the high radiant heat during multiple live fire drills each working day and as such the cardiovascular and thermal strain may be considerable. Although data are available on the physiological responses of fire-fighters during live fire-fighting drills no investigations have been undertaken to assess the cardiovascular and thermoregularory strain placed upon the instructors. PURPOSE: To characterize the physiological strain experienced by fire-instructors during a five day training program. METHODS: Six male instructors (mean±SD: age 34±8 yrs, height 1.80±0.03 cm, body mass 85±9 kg) were monitored over a five day work period. Measurements of heart rate (HR), core temperature (Tcore) and skin temperature (Tskin) were undertaken continuously throughout the day from 08:00 to 16:00 hours using the EquivitalTM-system (Hidalgo Ltd, Cambridge, UK). RESULTS: The mean basal (first 30 min of measurement) HR, Tcore and Tskin corresponded to 93.7±18.6bpm, 28.1±2.7°C and 37.0±0.4°C respectively. During fire drill scenarios the Tcore, HR and Tskin of individual instructors exhibited a dramatic increase. The highest individual HR, Tcore and Tskin recorded during the five day period corresponded to 189bpm, 40.7 and 41.8°C respectively. CONCLUSIONS: Despite not engaging in strenuous physical activity the data indicate that fire-fighting instructors experience considerable cardiovascular and thermal strain. The degree of thermal and cardiovascular challenge varies considerably between and within instructors and appears to be dependent on the particular fire drill they are involved with. Further work is warranted to better quantify the cardiovascular and thermal stain experienced by such instructors.
Repeated exposure to fire-fighting activities results in progressively greater physiological stress, which may pose a health risk to fire-fighters. Although the instructors who train fire-fighters are often exposed to multiple live fire drills during each working day few investigations have assessed the cumulative physiological strain placed on these individuals. PURPOSE: To determine to what extent day-to-day exposure to heat leads to an accumulation in physiological stress on fire-instructors throughout a five day training week. METHODS: Six male fire-instructors of the Royal Netherlands Air Force (RNLAF) Fire Academy (mean ± SD: age 38 ± 8 yrs, height 1.80 ± 0.03 cm, body mass 85 ± 9 kg) were monitored over a five day training week. During each training day the fire-instructors were exposed to (extreme) heat for three to four hours. Core temperature (Tcore) and heart rate (HR) rate were measured minute-by-minute throughout the day from 08:00 to 16:00h using the EquivitalTM-system (Hidalgo Ltd, Cambridge, UK). The cumulative effect was established by determining the baseline Tcore and HR on day one and identifying whether the Tcore and/or HR at the beginning of each subsequent training day were different compared with baseline. Baseline Tcore/HR was defined as the average Tcore/HR in the first 30 minutes of the first training day. RESULTS: For each individual fire-instructor, an increasing ΔTcore was found throughout the training week. With regard to the baseline values on the first training day, minimum individual ΔTcore-values varied from 0.17°C to 0.88°C on Day 2, while maximum individual ΔTcore-values varied from 0.24°C to 1.21°C on Day 4. A similar trend in HR-values was not found. CONCLUSION: Preliminary results indicate that a cumulative thermal effect occurs during the five day training week. This effect might be the result of the high daily thermal strain combined with an insufficient recovery between the working days. A structural recovery or rehabilitation stage at the end of each training day may facilitate instructors return to baseline physiological values.
During a day of skiing thousands of repeated contractions take place. Previous research on prolonged recreational alpine skiing show that physiological changes occur and hence some level of fatigue is inevitable. In the present paper the effect of prolonged skiing on the recruitment and coordination of the muscle activity was investigated. Six subjects performed 24 standardized runs. Muscle activity during the first two (PREskiing) and the last two (POSTskiing) runs was measured from the vastus lateralis (VL) and rectus femoris (RF) using EMG and quantified using wavelet and principal component analysis. The frequency content of the EMG signal shifted in seven out of eight cases significantly towards lower frequencies with highest effects observed for RF on outside leg. A significant pronounced outside leg loading occurred during POSTskiing and the timing of muscle activity peaks occurred more towards turn completion. Specific EMG frequency changes were observed at certain time points throughout the time windows and not over the whole double turn. It is suggested that general muscular fatigue, where additional specific muscle fibers have to be recruited due to the reduced power output of other fibers did not occur. The EMG frequency decrease and intensity changes for RF and VL are caused by altered timing (coordination) within the turn towards a most likely more uncontrolled skiing technique. Hence, these data provide evidence to suggest recreational skiers alter their skiing technique before a potential change in muscle fiber recruitment occurs. Key pointsThe frequency content of the EMG signal shifted in seven out of eight cases significantly towards lower frequencies with highest effects observed for RF.General muscular fatigue, where additional specific fibers have to be recruited due to the reduced power output of other fibers, did not occur.A modified skiing style towards a less functional and hence more uncontrolled skiing technique seems to be a key issue with respect to the influence on muscle recruitment for applied prolonged skiing session.
PURPOSE Early studies suggested that carbohydrate (CHO) ingestion shortly before endurance exercise may accelerate the rate of glycogen depletion, contribute to hypoglycemia and hasten fatigue. However, these studies have not used athletically meaningful outcomes, and have ignored the extensive warm-up often accomplished by athletes. This study evaluated the effect of 35 gm CHO consumption 30 min prior to a 40 km cycle time trial (TT). METHODS Well trained cyclists (n=10), habituated to TT, performed an intensive warm-up, ingested (in random order) either CHO or placebo, then performed TT. H2O was available ad libidum during TT. Outcomes were Time, Velocity, Power Output, HR, blood glucose (G) lactate (L), and rating of perceived exertion (RPE). RESULTS There was no significant (p < 0.05) difference (CHO vs P) in Time (74.31 vs 74.29 min), mean Power Output (194 vs 199 Watts), mean Velocity (9.00vs 9.04 m*s-1), HR (145 vs 145 bpm), blood lactate (3.84 vs 4.02 mmol*1–1) or blood glucose (4.84 vs 4.63 mmol*1–1). There were significant trends (p < 0.1) for Power Output and Velocity to increase during the latter portion of the CHO trial. In support of this finding, there was a trend (p = 0.07) for RPE to be lower throughout the CHO trial (5.35 vs 5.74). G was significantly higher at the beginning of the CHO trial (6.66 vs 4.88 mmol*1–1) and decreased during the first 5 km. After this point, however, there was no difference in G between CHO vs P. CONCLUSION The results suggest that pre-exercise feedings with CHO prior to TT is effectively neutral, which contradicts earlier studies using time to exhaustion rather than TT as an outcome measure. Trends within the data suggest that the ability to increase power output at the close of a TT may be facilitated by pre-exercise feedings.
Alzheimer's disease is the most common cause of dementia and affects 4 million people in the United States. A few studies have examined nongenetic risk factors for Alzheimer's disease such as diabetes, hypercholesterolemia, and hypertension. We are not aware of any studies that have examined Alzheimer's disease and cardiorespiratory fitness (CRF). PURPOSE To examine the effect of CRF as a predictor of Alzheimer's disease mortality in men and women. METHODS We followed 40,733 men and 13,258 women (aged 20–89 years at baseline) for up to 26 years. All participants completed a preventive health examination at the Cooper Clinic in Dallas, Texas during 1970–1996. CRF, calculated as METs, was measured by a maximal exercise test on a treadmill. Mortality surveillance was conducted principally through the National Death Index. We documented 41 Alzheimer's disease deaths during 665,090 person-years of observation. We used Cox proportional hazards models to evaluate CRF as a predictor of Alzheimer's disease mortality after adjustment for age, examination year, smoking habit, gender, and health status. RESULTS Older age was a significant predictor of increased Alzheimer's disease mortality. Male gender was nonsignificantly associated with greater risk. For each 1-MET increment in CRF, there was a 17% (95% CI, 0.4% to 30%) lower risk of Alzheimer's disease mortality. CONCLUSION CRF was inversely associated with Alzheimer's disease mortality in men and women. Supported in part by NIH grant AG06945.
PURPOSE:Assess the physical activity and body mass index (BMI) levels of children in the United States, Sweden, and Australia. METHODS:A total of 1954 children, 6-12 yr old (711 American, 563 Australian, and 680 Swedish) wore sealed pedometers for four consecutive days. Height and weight measures were obtained. RESULTS:Descriptive data for step counts and BMI by sex, age, and country were calculated to determine activity levels and BMI. Three-way multivariate ANOVA for step counts and BMI between countries at each age and sex found that, in general, the Swedish children were significantly more active than the Australian and American children, and the American children were significantly heavier than the Australian and Swedish children. For boys, the mean step counts ranged from 15673 to 18346 for Sweden, 13864 to 15023 for Australia, and 12554 to 13872 for America. For girls, the mean step counts ranged from 12041 to 14825 for Sweden, 11221 to 12322 for Australia, and 10661 to 11383 for America. The activity curve is somewhat level during the preadolescent years. The rate of increase in BMI with age is much greater in the American children than in the Swedish or Australian children. The percent of American, Swedish, and Australian boys classified as overweight/obese was 33.5, 16.6, and 15.8, respectively. The percent of American, Swedish, and Australian girls classified as overweight/obese was 35.6, 16.8, and 14.4, respectively. Correlation analysis found few significant negative relationships between step counts and BMI. CONCLUSIONS:American children tend to be the least active and heaviest with the greatest rate of increase in BMI. The Swedish children are the most active group followed by Australia. Swedish and Australian children maintain lower BMI throughout their prepubescent years than do the American children who have a greater percentage who are classified as overweight.
Differentiated ratings of perceived exertion, using Children Effort Rating Table, CERT, and oxygen consumption were determined while carrying loads during flat and grade (6%) walking in obese (OB, n = 15) and lean (LE, n = 15) boys. Subjects walked on treadmill for 6 min at 6 km.h−1 while carrying no load (NL), a load equal to 15% of lean body mass (LBM), and a load equal to 15% of body mass (BM). Loads were distributed evenly on the trunk with a worn vest. Testing was performed in a counterbalanced order. Means (± SD) of age, weight, and fat content for OB vs. LE boys were: 10.59 ± 0.14 vs. 10.62 ± 0.18 yr; 47.7 ± 5.4 vs. 28.6 ± 3.4 kg; 37.2 ± 3.9 vs. 14.3 ± 2.8%, respectively. Central (C), and local (L) ratings were not different (P < .05) from overall (O) rating in both groups during flat and grade walking with NL. Lean boys had higher (P < .05) O rating than L rating during flat walking with both loads and during grade walking with LBM load. However, only during grade walking with LBM load had OB boys higher (P < .05) O rating than L, and higher (P < .05) O than L & C with BM load. There was a group by grade interaction where LE boys exhibited higher C, L, and O ratings during grade compared to flat walking with BM load. Oxygen consumption (ml.kg−1.min−1), while adjusting for O2 cost of walking without load, was higher (P < .05) in LE than in OB during grade walking with both LBM and BM loads. This could partially explain why LE boys had higher perceptual ratings during grade walking in comparison with flat walking.
The kinetics of muscle oxygenation was determined by continuous-wave Near Infrared Spectroscopy (NIRS) in 8 healthy untrained subjects (age 26.3 ± 0.8 yr [x ± SE], VO2max 39.6 ± 1.4 ml/kg/min) during transitions from unloaded pedaling to 5-min constantload cycling at workloads below the ventilatory threshold (< VT) and between VT and VO2max (> VT). Concentration changes of oxygenated Hb (Δ[O2Hb]) and deoxygenated Hb (Δ[HHb]) were determined by NIRS (HEO-100, Omron) in a superficial region of the vastus lateralis. Breath-by-breath pulmonary gas exchange was determined at the mouth. At the transition, Δ[HHb] increased following a time-course that was nicely fitted by a monoexponential function, characterized by a time-delay (TD) (during which Δ[HHb] was substantially unchanged compared to baseline) and a time-constant (τ). Δ[O2Hb] showed, after an initial monoexponential decrease (mirror image of the Δ[HHb increase]), a partial increase associated with an increase of the total Hb volume (Δ[O2Hb+HHb]). TD of the Δ[HHb] on-kinetics was 6.5 ± 0.7 s (< VT) and 2.9 ± 0.7 s (> VT) (P = 0.04), whereas τ was 9.0 ± 1.1 s(< VT) and 9.9 ± 0.7 s(> VT) (NS). Steady-state Δ[HHb] increases during exercise were 58 ± 6% (< VT) and 80 ± 5% (> VT) (P = 0.001) of those observed during leg ischemia induced by cuff inflation for > 3 min at ∼300 mmHg. Individual values of the sum between TD and τ of Δ[HHb] on-kinetics were significantly correlated (P = 0.03, r = 0.54) with the τ of the oprimaryö component of the pulmonary VO2 on-kinetics (26.6 ± 2.5 s for < VT, and 31.6 ± 1.8 s for > VT). The unchanged Δ[HHb] during the first few seconds of the transition suggests adequacy of O2 delivery in relation to O2 demand. Non-invasive evaluation of muscle oxygenation by NIRS could represent a valuable tool for functional evaluation of the kinetics of skeletal muscle oxidative metabolism. (Supported by NATO CRG 972111, and by Telethon Italy Grant n. 1161C)
