STUDIES IN PHYSICAL CULTURE AND TOURISM

Vol. 12, No. 1, 2005

The purpose of this study was to estimate the level of anaerobic-phosphogenic power changes and force-velocity components of P_max in middle-aged men. 15 middle-aged men and 52 physical education students were studied. The middle-aged men were tested twice: 5 years ago – lower body work only (LB), and at present – both upper (UB) and lower body work. The students were tested once (upper and lower body work). The tests were performed on the Monark cycle ergometer. Anaerobic power was estimated using relationship between force and velocity (F-V) at work on the Monark cycle ergometer, for lower and upper body work according to the method developed by Vandewalle et al. To calculate maximal power (P_max) V₀ and F₀ was estimated. V₀ is the intercept of the force-velocity regression line with velocity axis and, F₀ – the intercept of the regression line with the force axis. P_max was expressed in watts [W] and was calculated to kg body mass (BM). The study showed that differences between P_max and F₀ obtained during lower and upper body work in students and middle-aged men were significant. However, the level of P_max and its components was not significantly different after 5 years in middle aged men (p≥0.05).

Studies concerning estimation of anaerobic-phosphagenic power in middle-aged people, which have been carried out so far, are fairly limited. However, the research which has been done reveals a gradual reduction of anaerobic efficiency with age [1, 5]. The decrease of force-velocity abilities with age is connected with the changes in mass and muscle fibres (mainly FT) cross-section, and an increase of fibre cross-section index (ST/FT). Moreover, reduction in anaerobic efficiency in middle-aged people can be caused by deterioration of neuro-muscular coordination [20], and decline of activity of anaerobic enzymes. However, the data concerning this issue are contradictory (such deterioration was noticed by Larsson and Karlsson [15], but not by Fleg [9]). Grimby and Saltin [12] and Frontera [10] reported that reduction of men’s strength with age was more significant in lower limb muscles than in upper ones. However, few authors have examined the abilities to develop upper limb muscle power in people at different age, as compared to lower limb muscle power.

The aim of this study was to examine the level of anaerobic-phosphagenic power and its components (force and velocity) in middle-aged men in relation to young men, and the changes occurring in middle-aged men at a five-year interval.

Subjects from two age groups: 15 middle-aged men (M), 51.0 ± 4.6 yrs, and 52 male students of physical education (S), aged 23.8 ± 4.1, were tested. The subjects led a physically active lifestyle; 10 out of 15 middle-aged men played tennis, basketball, football twice a week; whereas the students participated in obligatory exercises (two hours a week: basketball, football, swimming, running). Biometrical characteristics of both groups are shown in Table 1.

Table 1. Biometrical characteristic of subjects

The tests were conducted in pre-afternoon hours by the same persons using the same methods. Participation in the experiments was voluntary, with a doctor’s consent. The experiments were approved by the Local Committee for Ethics and Scientific Research in Poznań.

Anaerobic power was estimated using the relationship between force and velocity (F-V) at work on the Monark 814 E cycle ergometr, for lower (LB) and upper body (UB) work, according to the method in Vandewalle et al. [19]. To calculate maximal power (P_max), V₀ and F₀ were estimated. V₀ is the intercept of the force-velocity regression line with velocity axis; and F₀ is the intercept of the regression line with the force axis. P_max was calculated to kg body mass (BM) and kg lean body mass (LBM). Fat mass and lean body mass were estimated using bioelectrical impedance method (RJL Systems, Inc).

Each subject performed 5 or 6 exercises on a cycle ergometer (LB) and 5 or 6 exercises on an arms ergometer (UB). Subjects were motivated to reach a maximal velocity of pedal revolutions during each attempt. Different load was applied and the attempts were performed with the velocity range between 100 and 200 rpm. Five years earlier the men from the M group had been examined using precisely the same procedure; but on lower limbs only.

The results are reported as mean values with standard deviations. The t-test was used to calculate the differences between groups; p≤0.05 was considered statistically significant.

A comparison of parameters obtained during lower and upper body work by the middle-aged men and students revealed significant differences (p≤0.05) in P_max. Maximal power obtained during the lower body test by M group was 1036W (12.5W/kg) and S group – 1244W (16.1W/kg) (Fig. 1).

Figure 1. Maximal anaerobic power achieved during lower body work

The lower value of P_max obtained by M group was caused by the lower value of F₀ (191 N) in M group, comparing to the students’ group (237 N) (Fig. 2). Differences in the V₀ component in the cycle ergometer test were not significant (218 rpm – M group and 212 rpm – S group).

Figure 2. Force component achieved during lower body work

Similar trends were observed in the arm test. P_max obtained by M group (760W; 9.2W/kg) was 18% lower than in S group (925W; 12W/kg) (Fig. 3). In this case the lower value of P_max was also caused by the lower F₀ component, similar to the legs test (147 N and 178 N) (Fig. 4). Both groups achieved almost the same level of V₀ component: M group-202 rpm and S-210 rpm. The differences were not significant.

Figure 3. Maximal anaerobic power achieved during upper body work

Figure 4. Force component achieved during upper body work

Figure 5. Percentage level of P_max obtained by both groups during upper and lower body work

Both groups achieved higher values of P_max during lower limb than upper limb work. P_max obtained by both groups during the upper body test achieved almost the same level of P_max (about 75%) obtained during the lower body test (Fig. 5).

Differences between maximal anaerobic power obtained by the middle-aged men group during lower body work in the first test (five years ago) and at present were not significant.

P_max reached during the first test was 1021W (12.6W/kg), and 1036W (12.5W/kg) after five years. Similar trends were observed in P_max components: V₀ and F₀ (Tab. 2).

Maximal power is a better indicator of the muscle efficiency than strength, especially in old men [4]. For that reason, it is very important to maintain P_max at the possible highest level even in old age, because it decides about our safety in various situations. A high level of anaerobic-phospha-genic power depends not only on a high level of muscle strength, but also on efficient neuro-muscular coordination.

The results achieved in this research confirm the reduction in the level of developed maximal power with age [6, 8, 11]. P_max expressed in Watts [W] achieved by middle-aged men is 17% lower during lower limb and 18% lower during upper limb work, in comparison with the group of students. However, our results show smaller than in other authors, differences in developed power between the examined groups. Grassi et al. [11] have proved linear reduction in anaerobic efficiency in the amount of 1% every year and until the age 45,

Table 2. Anaerobic efficiency characteristic in lower-limb test during the first and second examination for middle-aged men

being probably a result of deterioration in neuro-muscular coordination. Similar trends were also observed by Ecker [6]. Moreover, results obtained by other authors show that the level of maximum power decreases faster than strength (about 3.5% per year after the age of 60) [2, 13]. The level of maximum power achieved by the older group in the first and second research (five years ago and at present) was similar. However, P_max obtained by M group is significantly lower than P_max in students’ group. That probably indicates a reduction in maximum power that took place before the first test. The P_max drop can result from a muscle fibres (FT) cross-section decrease, a decrease in the single muscle fibres contraction velocity [15], decrease of neurons conduction velocity [7] and the activity of anaerobic enzymes [3, 17]. It can also be caused by a decrease in physical activity. However, our experiment showed that physical active live style enabled the subjects to maintain maximal power at the same level even until the later middle-age period of life (46-51 years).

Notwithstanding, our results also show a higher decline of maximum power with age, when P_max is expressed in watts per kg than in watts. The middle-aged men obtained 22% of the P_max [W/kg] value achieved by the students for lower limbs and 23% for upper limbs. It is quite unexpected, because Grimby’s and Saltin’s [12] or Mc Donagh’s [16] studies showed that a decrease in the ability to develop high muscle strength with age, proceeded faster in lower than upper limbs. It probably results from the lack of trunk stabilization during our tests. For this reason, other groups of trunk muscles could have an influence on the achieved power.

Lower maximal power achieved in the present study in the middle-aged group (in comparison with the students) can be caused by an age-related deficit in the ability to perform rapid repetitive dynamic contractions, demanding cooperation of different muscle groups [14]. Changes in coordination of antagonistic muscles exciting and relaxation processes can also have an impact on lower P_max [18]. During maximal effort intensity, recruitment of high-threshold (FT) motor units is necessary [8]. Deterioration of fast twitch motor unit recruitment can thus contribute to lower maximal power in middle-aged men.

The comparison between the two groups (M and S) shows that the reduction in the achieved power during lower and upper limbs work (p≤ 0.05) with age is caused by a decrease in the force component (F₀). The other component (V₀) is similar in both groups. Lack of differences in V₀ between the examined groups can suggest that active life style led by middle-aged men may counteract the decline of this feature.

Comparing the results obtained by the middle-aged men five years ago and at present it seems evident that the maximal phosphagenic power remains on a constant level in this group. Differences between maximal anaerobic power and its components obtained by middle-aged men during lower body work in the first test and at present were not significant. It can be connected with the same value of muscle mass in kg measured during the two tests. However, due to a higher fat content, body mass was higher after five years. The middle-aged men have led an active lifestyle, so it is possible that the 5-year period between the first and the second test was too short to observe any significant changes in maximal power for that specific subject group. Moreover, our research shows that active life style at the middle age can decrease the involution process rate.

Our results allowed us to draw the following conclusions: