Age-related maximal heart rate: examination and refinement of prediction equations

AIM

The aim of this study was to establish the maximal heart rate (HRmax)-age relation with minimal error rate.

METHODS

The records of 28,137 participants (20,691 male and 7446 female, age range between 10 and 80 yrs) who performed a maximal stress test were used in this study. Linear regressions between HRmax and age were used for the entire sample, for the male and female samples, separately, and for each section of the gender-by-age category. The equations were then contrasted to a number of equations reported in the literature. The best fitted equations were then tested on a new sample of 2449 subjects (2091 males and 358 females) for validation purposes.

RESULTS

Mean HRmax values were found to decrease at a faster rate in women than in men with age increase. The linear regression functions within each age category were found to be less reliable than the equations derived for the entire sample and for the female and male samples, respectively. The new and updated HRmax prediction equations are as follows: HRmax=208.609-0.716age and 209.273-0.804age for males and females, respectively, and 208.852-0.741age for the entire sample. Those equations along with the other four best equations for predicting HRmax were found to be correlated with the observed HRmax values (validation sample): 0.64 and 0.664 for males and females, respectively.

CONCLUSION

Our equations were derived from a large data set and were found to be highly sensitive for both genders. Therefore, we propose that these new formulas, with their improved accuracy, be used in healthy active and clinical populations.

Heart rate monitoring as a reliable tool for assessing energy expenditure in obese individuals

Previous studies have suggested the use of the FlexHR method for predicting daily energy expenditure in various populations. We investigated the stability of the relation between oxygen consumption (VO2) and heart rate (HR) in obese subjects undergoing a fitness and weight reduction program. Eleven obese (BMI>30) healthy subjects (6 males, 5 females) were recruited from a Wellness program. Subjects performed a laboratory calibration procedure between HR and VO2 in resting and exercising conditions, before starting the Wellness program (Stage I) and after reducing 10% of their initial body weights (BW) within 6 months (Stage II). Mean BW, BMI and % body fat were reduced by 13.1±4.4 kg, 4.2±1.4 kg.m-2 and 6.8±4.1%, respectively, for all parameters (P<0.001). Mean peak VO2 increased from 31.3±7.1 at the beginning to 37.2±7.3 mL.kg-1.min-1 at the end of the intervention period (P<0.01). The mean flex HR point changed from 96±14 to 86±15 beats.min-1 (P<0.05). There were no significant individual differences in the HR-VO2 prediction equations derived from the laboratory calibrations in either stage. In conclusion, the relationship between HR and VO2 consumption remains stable during a time period of weight reduction. The use of the FlexHR method for predicting energy expenditure by heart rate monitoring is recommended for subjects undergoing a weight-reduction program. It should be taken in account, however, that an increase in aerobic capacity, in parallel to changes in body weight and composition, might cause a decrease in the flex point.

Reliability and validity of the lactate-minimum test. A revisit

AIM

The Lactate-Minimum Test (LMT) is a high-resolution, physiologically elegant test for estimating the anaerobic threshold (AnT), or the Maximal Lactate Steady-State (MLSS). Nevertheless, it has not gained the acceptance level of typical progressive lactate-response tests (PLRT). Aim of this study was to compare LMT's validity and reviewer reliability vs. a PLRT-type test and re-evaluate the justification for LMT's dismissal.

METHODS

Sixteen male distance trained runners (37.1±11.6 yrs) were included in the study. MLSS, LMT, and PLRT tests were performed in separate sessions. Two reviewers, blind to the subjects' identity, independently determined LMT and PLRT's threshold velocities (VLMT, VPLRT) twice. Additionally, VLMT was determined objectively, using best-fit polynomial regressions (VLMTP).

RESULTS

VPLRT, VLMT and VLMTP correlated well with VMLSS (r=0.92, 0.90, 0.93, resp.). VPLRT was identical to VMLSS (13.54 km·h-1), but VLMT and VLMTP were 0.33 and 0.46 km·h-1 lower, respectively. Inter-reviewer reliability was higher for VLMT than VPLRT (ICC=0.96 vs. 0.57, resp.). Intra-reviewer reliability showed a similar pattern.

CONCLUSION

LMT's underestimation of MLSS appears corrigible. The validity of corrected LMT appears comparable to that of PLRT, while its reliability, objectivity and resolution are superior. Although neither test is a perfect MLSS-substitute, the corrected LMT is not inferior to PLRT-type testing and cannot be dismissed.

A cumulative effect of physical training on bone strength in males

Weight-bearing, high-impact exercise, as opposed to nonimpact exercise, has been demonstrated to increase bone mineral density. This was traditionally demonstrated with dual energy X-ray absorptiometry. Our objective was to assess the differences in bone properties, using quantitative ultrasound (QUS, Sunlight Omnisense, Sunlight Medical, Ltd., Tel Aviv, Israel), in male athletes involved in a weight-bearing, impact sport (soccer, SC) or a nonimpact sport (swimming and water polo, AQ), compared with nonathletic control (C) males. A total of 266 boys and men, aged 8 - 23 years, were divided into children (11.1 +/- 1.0 years; 34 SC, 34 AQ, 25 C), adolescents (14.7 +/- 1.2 years; 32 SC, 31 AQ, 31 C), and young adults (19.8 +/- 1.1 years; 31 SC, 24 AQ, 24 C) . Training experience varied between 1.5 years in the children to 15 years in the adults. Bone speed of sound (SOS) was measured bilaterally at the distal radius and the mid-tibia. Body fat was significantly lower in athletes compared with C. AQ were generally heavier and had a higher fat-free mass compared with SC and C, with no significant differences in height between groups. Radial SOS increased with age, but no differences were observed between activity groups or between the dominant (D) and nondominant (ND) arm. Tibial SOS also increased with age. In the children and adolescents, no differences were observed between activity groups. However, among adults, both SC and AQ had higher tibial SOS compared with C. These differences were mainly explained by differences in fat-free mass. Among young adults but not among children and adolescent males, both soccer and aquatic sports appear to be associated with higher bone SOS in the lower, but not the upper, extremities. Further studies are needed to assess possible sport-specific mechanisms which affect bone properties and to determine the minimal cumulative effect which is needed to influence bone properties.

Bone properties and muscle strength of young haemophilia patients

PURPOSE

To evaluate bone properties, muscle strength and the relationship between the two, in young (7.0-17.7 years) haemophilia patients (h) and healthy boys (c).

SUBJECTS

Twenty-seven boys with severe haemophilia and 33 healthy boys, of similar age, body mass, height, (mean +/- sd for h and c, respectively: 11.2 +/- 3.2 vs. 11.4 +/- 2.9 years, 42.6 +/- 16.6 vs. 41.6 +/- 17.3 kg, 145 +/- 18 vs. 146 +/- 17 cm) and pubertal stage according to secondary sex characteristics, volunteered for the study. all subjects were physically inactive (as determined by questionnaire).

METHODS

Subjects performed isokinetic elbow and knee extension and flexion tests at two angular velocities (biodex system ii dynamometer). Bone properties were evaluated by qualitative ultrasound (sunlight omnisense), at the distal radius and tibial mid-shaft. H subjects received prophylactic factor viii treatment within the 24 h preceding testing. No test was performed in the presence of haemorrhage.

RESULTS

Muscle strength was consistently higher in c compared with h, especially in the lower limbs (e.g. knee extension: 1.80 +/- 0.44 vs 1.48 +/- 0.53 N x m x kg(-1) body mass, respectively, p = 0.01). No differences were observed in tibial or radial speed of sound between groups. Correlations between muscle strength and bone properties were observed only in the lower limbs and only in c (r = 0.37-0.48).

CONCLUSION

Muscle strength, especially lower limbs' strength, was lower in haemophilia patients compared with a matched, similarly inactive population of healthy boys. Nevertheless, at this age range, this relative weakness is not associated with inferior bone properties.

Higher tibial quantitative ultrasound in young female swimmers

BACKGROUND

It has been found that swimming, a non-impact sport, generally has no effect on bone mineral density.

OBJECTIVES

To examine bone properties, as measured by quantitative ultrasound, among female swimmers in comparison with control girls and women.

METHODS

Subjects included 61 swimmers and 71 controls aged 8.5 to 26.5 years. None of the swimmers was at the elite level and none had included resistance training in her schedule. Bone speed of sound (SOS) was measured bilaterally at the distal radius and the mid-tibia.

RESULTS

No differences were observed between swimmers and controls in body mass (mean (SD): 49.7 (12.3) v 50.7 (12.4) kg, respectively), although swimmers were taller (159 (12) v 155 (12) cm) and had lower body fat (18.3 (4.2)% v 22.3 (5.4)%). No difference was found in time since menarche (5.2 (4.0) and 4.5 (2.9) years in swimmers and controls, respectively; 21 swimmers and 25 control were premenarcheal). Radial speed of sound (SOS) increased with age but did not differ between swimmers and controls (non-dominant: 3904 (172) and 3889 (165) m/s for swimmers and controls, respectively). Tibial SOS also increased with age and was significantly higher in swimmers than in controls (non-dominant: 3774 (155) v 3712 (171) m/s). No differences were found between dominant and non-dominant sides.

CONCLUSIONS

Swimming appears to be associated with higher bone SOS in the lower but not in the upper extremities. Further studies are needed to assess whether this difference reflects higher habitual activity among the swimmers or swimming specific mechanisms.

The association between adiposity and the response to resistance training among pre- and early-pubertal boys

Resistance training has been shown to be effective in enhancing muscle strength among prepubertal and adolescent boys. Lately, it has been recommended for obese children. We hypothesized that resistance training will be similarly effective among boys of different adiposity. Thirty boys, aged 9.2 +/- 0.3 years, participated in progressive resistance training twice weekly during the first and second school years and thrice weekly during the third year. Training sessions included 1-4 sets of 3-6 exercises, with 5-30 repetitions/set. The mean load was 50-60% of 1 repetition maximum. Subjects were divided into responders (R--upper tertile) and non-responders (NR--lower tertile), according to the three-year improvement in muscle strength, as assessed by means of changes in concentric strength of knee flexors and extensors. Differences between groups were observed at baseline (p <0.05) in all variables reflecting adiposity (mean +/- SD): % body fat (14.1 +/- 2.6 vs 23.5 +/- 7.5% for R and NR, respectively), sum of four skinfolds (25.4 +/- 4.7 vs 47.8 +/- 21.6 mm for R and NR, respectively), BMI (15.5 +/- 1.1 vs 18.6 +/- 2.6 kg x m(-2) for R and NR, respectively). Additionally, the changes in adiposity were inversely related to the training effect (r = -0.60 to -0.34). No differences were observed in initial height and maturation between R and NR groups and there was no difference in linear growth and physical maturation with time between groups. These data suggest that resistance-training loads which may be appropriate to increase strength of knee flexors and extensors in normal-weight children may be insufficient to do so in overweight children. More research is required to elucidate the efficacy of resistance training among overweight children.

Quantitative ultrasound (QUS) of the tibia: a sensitive tool for the detection of bone changes in growing boys

The purpose of this study was to determine whether growth-related changes in bone properties can be detected in prepubertal boys using quantitative ultrasound (QUS) and to determine whether resistance training stimulates bone changes. Two groups, each of thirty 9-10 year-old boys, participated in regular physical education classes or in resistance training. Tibial speed of sound (SOS) (SoundScan 2000, Myriad) was assessed at the beginning of the school year and after 8 months. At baseline, there were no differences between groups in tibial SOS, anthropometric measures or pubertal development. At the end of the year, the tibial SOS increased (p<0.001) in both groups to a similar extent. In addition, there were no differences in the increases in height between the two groups. This indicates that resistance training during the physical education program did not induce changes in bone beyond what would be expected by the mere effect of growing. We conclude that changes in tibial SOS, as obtained with QUS, can be detected in groups of prepubertal boys over a period of 8 months.

Iron status of highly active adolescents: evidence of depleted iron stores in gymnasts

Much attention has focused on the nutrition and hematological profile of female athletes, especially gymnasts. The few studies on iron status of male adolescent athletes found a low incidence of iron deficiency. The present studies investigated the iron status of male and female gymnasts (G) and compared it with athletes of other sports. Subjects were 68 elite athletes (43 M, 25F) ages 12-18, of four sports: gymnasts (11M,12F), swimmers (11M,6F), tennis players (10M,4F), and table tennis players (11M,3F). All lived in the national center for gifted athletes, trained over 25 hr a week, ate in the same dining room, and shared a similar life style. Mean levels of hemoglobin (Hb), red blood cell indexes, serum ferritin, serum iron, and transferrin were measured in venous blood. There was no difference in mean Rb among gymnasts (G) and nongymnasts (NG). However Hb was less than 14g/dL in 45% of MG vs. only 25% in NG, and less than 13g/dL in 25% of premenarcheal FG vs. 15% in NG. Low transferrin saturation (<20%) was detected in 18% of MG and 25% of FG vs. 6% and 8% in male and female NG, respectively (p<.05). The percentage of males suffering from low ferritin level (<20 ng/ml) was twice as high in G (36%) vs. NG(19%), and about 30% in all females. In summary, iron stores were consistently lower in MG vs. NG. Adolescent athletes of both genders, G in particular, are prone to nonanemic iron deficiency, which might compromise their health and athletic performance.

Changes in plasma volume following intense intermittent exercise in neutral and hot environmental conditions

BACKGROUND

The purpose of the present investigation was to examine the effect of supramaximal short duration intermittent exercise in neutral and hot environmental conditions on changes in plasma volume. The return of plasma volume (PV) to pre-exercise values following different recovery conditions was also examined.

METHODS

Experimental design. Within subject design in which one way analysis of variance was conducted.

SETTING

Research, sports science academic institute.

PARTICIPANTS

Ten trained men, 25.5 +/- 3/1 (yrs), volunteers.

INTERVENTIONS

Subjects performed six 1-min bouts of exercise at 100% VO2peak on a cycle ergometer, with 4-min rest intervals between the bouts. Each subject exercised twice in thermoneutral (22 degrees C, 40% RH) and twice in hot (35 degrees C, 30% RH) conditions. Exercise was followed by either 40 min of passive recovery (sitting) or by 20 min active recovery (cycling at 35% VO2peak) and 20 min passive recovery, named thereafter "active recovery".

MEASURES

Hematocrit (Hct) and hemoglobin (Hb) were determined upon entry into the climatic chamber following 20 min rest in the chamber (pre-exercise), immediately postexercise, and 40 min postexercise. From the changes in Hct and Hb, PV changes were calculated.

RESULTS

There was a significant decrease in PV immediately postexercise. However, there was no significant difference between the two types of environmental conditions and no difference between the two types of recovery. PV increased significantly following recovery and returned to pre-exercise values following 40 min of recovery.

CONCLUSIONS

Changes in PV caused by maximal short duration cycling bouts is not affected by environmental conditions, PV returns to its pre-exercise values within 40 min of recovery regardless of the recovery mode.