Psychological effects of strength training on children.

Faigenbaum, Avery ; Zaichowsky, Leonard D. ; Westcott, Wayne L. 等

Strength training is often prescribed as part of a well-rounded exercise program for adults and its popularity among children continues to increase. Previously deemed unsafe and ineffective for children (American Academy of Pediatrics, 1983), strength training is now considered an important component of youth fitness conditioning programs (American Orthopaedic Society for Sports Medicine, 1988; Faigenbaum, Kraemer et al., 1996) and injury prevention strategies (American College of Sports Medicine, 1993). Improvements in various anatomical and physiological measures have been noted in children who have participated in appropriately designed and well-supervised strength training programs (Faigenbaum, 1993). Related information on the psychological benefits of youth strength training is limited, however.

Data from adult populations demonstrate that the effects of strength training extend beyond physical measures and include improvements in mental health and well-being (Dishman & Gettman, 1981; Doyne, et al., 1987; Melnick & Mookerjee, 1991; Stein & Motta, 1992; Tucker, 1982, 1983a). Tucker (1982) reported significantly higher values for self-concept and self-esteem (1983) in college-age men who participated in a strength training program and similar findings involving college-age men and women were reported by Melnick and Mookerjee (1991). Strength training has improved psychic vigor and physical self-esteem in men (Dishman & Geltman, 1981), and strength training appears to be just as effective as aerobic exercise in reducing clinical depression in women (Doyne et al., 1987; Stein & Motta, 1992). In the clinical setting, adult patients with higher ratings of arm strength self-efficacy achieved greater gains in arm strength than did patients with lower arm strength-self efficacy ratings (Ewart, Taylor, Reese, & DeBusk, 1983). Self-efficacy expectations appear to be meaningful determinants of exercise behavior in adults (Bandura, 1977, 1986), and may provide important information regarding the acquisition of new behaviors in younger populations. As such, self efficacy was selected as an outcome measure for this study.

Children who participate in physical fitness programs are reported to have higher self-concepts that those who are inactive (Zaichkowsky, L., Zaichkowsky, L., & Martinek, T., 1975; Martinek, T., Cheffers, J., & Zaichkowsky, L., 1978), although not all studies have reported positive relationships between fitness and childhood self-esteem (Kay, Felker, & Varoz, 1972). Despite these inconsistencies, a recent review on this topic suggests that children who participate in appropriately prescribed aerobic exercise programs have the potential to increase their self-efficacy, creativity, self-esteem, internal locus of control, test scores on cognitive functioning and classroom behavior (Welsh & Labbe, 1994).

Holloway, Beuter, and Duda (1988) reported that adolescent females who strength trained significantly improved their situationally specific self-efficacy expectations about strength training and other less-related tasks such as confrontation. In younger populations, anecdotal reports from prepubescent boys and girls and their parents suggest that strength training may positively influence socialization skills, mental discipline and self-concept (Faigenbaum, 1995). At this time, however, controlled studies exploring the potential psychological benefits of prepubescent strength training have not yet been performed.

Since the psychological benefits of aerobic exercise on children have been documented in the literature (Welsh & Labbe, 1994), it is reasonable to assume that anaerobic types of exercise such as strength training may also provide psychological beneficence. The popularity of strength training activities continues to increase and youth strength training programs have become important components of public health objectives (Department of Health and Human Services, 1990). Although information from adult studies is useful, speculations regarding the psychosocial benefits of strength training for children are limited because of the psychological and physical immaturity of children. Moreover, the type of strength training program most likely to enhance psychological well-being remains hypothetical because the acute program variables (e.g., choice of exercises, order of exercises, repetitions, sets and rest periods) are not defined in most of the psychological reports involving adults.

The specific purpose of this study was to investigate the effects of strength training on the global self-concepts and situationally specific self-efficacy levels of prepubescent boys and girls. The strength training program in this study was designed to safely maximize strength gains in children while offering a progression of mastery experiences that might influence psychological well-being. Both physical and psychological parameters were clearly described in order to assess the interaction between these variables. It was hypothesized that increases in strength would positively influence scores on self-concept and related self-efficacy measures.

Method

Subjects

Twenty-four boys and girls living in a suburb of Boston, Massachusetts volunteered to take part in this study. The subjects were white and from predominantly middle income level families. Parental written consent was obtained. A physician conducted a medical examination on all subjects in order to evaluate musculoskeletal status, document preexisting orthopedic injuries and assess maturity status based on Tanner staging of pubic hair development (Tanner, 1962). Males and females were combined in this study because they perform equally well on strength tests during preadolescence (Blimkie, 1989). Moreover, sex differences in self-concept for elementary-age boys and girls is small (Zaichkowsky, Zaichkowsky, & Martinek, 1980).

The experimental group consisted of 11 boys and 4 girls (mean age 10.8 [+ or -] 0.4 years) who enrolled in this study prior to the recruitment of the control group which included 3 boys and 6 girls (mean age 10.0 [+ or -] 0.4 yrs). Administrative variables (e.g., the availability of space, time, and equipment) precluded the enrollment of additional subjects. Tanner staging for maturity level revealed that the experimental group consisted of 13 subjects at Tanner stage 1 and 2 subjects at Tanner stage 2, while the control group had 8 subjects at Tanner stage 1 and I subject at Tanner stage 9. There were no significant differences between the two groups for age or Tanner scale rating (p [greater than] 0.05). Subjects did not have any prior experience with strength training. All volunteers were accepted for participation.

Design and Procedure

All testing and training took place during the summer at a local youth fitness center. At least two instructors, including one certified Health/Fitness Director (American College of Sports Medicine, 1995), supervised all sessions. Experimental and control group subjects were taught the proper form and technique on each exercise during two introductory sessions within a one week period. Physical strength was assessed following the one week introductory period and at the conclusion of the study. Details of the testing and training protocols have been described in a previous report (Faigenbaum, Westcott et al., 1996). Psychological measures were assessed before and after the strength training program.

Strength Measures

Each subject's 6 repetition maximum (RM) was determined on the leg extension and chest press. The maximum weight that could be lifted six times using the correct form was recorded. Following a 72-hour rest period, both 6 RM measures were reevaluated. The heaviest 6 RM load lifted on each exercise, on either testing day, was recorded as the child's criterion 6 RM score.

Psychological Measures

Self Concept. The Martinek-Zaichkowsky Self Concept Scale for Children (MZSCS) (Martinek & Zaichkowsky, 1977) was used to evaluate global self-concept development in the children. This nonverbal test consists of 25 pairs of cartoon pictures (1-point each) and measures intellectual, social, and physical aspects of a child's self-concept as well as appropriate behavior. The subjects were asked to mark the pictures which were most like them. The test has acceptable validity, internal consistency, and stability (Martinek & Zaichkowsky, 1977).

Self-Efficacy. A modified version of the scale developed by Ewart (1990) was created for this study to assess each child's self-perceived efficacy (confidence) in performing specific tasks involving strength. The questions were presented in a Likert scale in which the children rated their perceived weight lifting ability on an 11-point probability scale ranging from "definitely cannot do it" (O-points) to "definitely can do it" (10-points). The children were presented with a series of progressively more difficult physical tasks (i.e., the ability to lift 5, 10, 15...50 pounds with their upper body and 5, 10, 15...60 pounds with their lower body) and were asked to rate the strength of their perceived ability to perform the task at that specific moment. A subject's self-efficacy construct score was the sum of the confidence estimates for successive levels of a specific task divided by the total number of items. Previous studies of self-efficacy have employed a similar testing methodology (Bandura & Adams, 1977; Ewart et al., 1983; Holloway et al., 1988).

Training Program

Subjects in the experimental group trained twice per week (Monday and Wednesday) for eight weeks under qualified adult supervision. Throughout the training program, an instructor to subject ratio of at least 1 to 4 was maintained at all times. Daily instructional sessions focused on proper exercise technique, and any questions from the subjects were answered. During the first four weeks of training, subjects performed one warm-up set of 10 repetitions followed by two sets of six to eight repetitions on the leg extension, chest press, leg curl, overhead press and biceps curl. During the last four weeks of training, subjects performed three sets of six to eight repetitions on the chest press and leg extension whereas the number of sets on the other exercises remained unchanged. Child-size dynamic constant resistance equipment (Heartline Fitness Equipment, Gaithersburg, MD) was used for all strength testing and training procedures. The predetermined 6 repetition maximum (RM) load was used for the leg extension and chest press whereas initial 6 RM training loads for the other exercises were estimated during the first week of training. Once 8 repetitions could be performed on the last set, the resistance was increased by 5 to 10% and the repetitions were decreased to 6. Each session included flexibility exercises and lasted about one hour. Subjects exercised with a partner and recorded their data on workout logs which were reviewed daily by the instructors who made appropriate adjustments in training loads and repetitions if necessary. If an exercise session was missed, a makeup session was offered during the same week. Experimental and control group subjects were asked not to partake in any strength training activities outside of the supervised research setting. However, all subjects were permitted to continue participation In organized sport activities (primarily baseball, soccer or swimming) throughout the study.

Results

All subjects completed the study according to the aforementioned methodology. The strength trained subjects had an average attendance rate of 93%.

Analysis of covariance procedures were performed on the post-test scores for each of the dependent variables using the pretest scores for each variable as the covariate. This procedure adjusted for initial variability in pretest scores between subjects. Adjusted post-means are presented in Table 1. Group data are reported as mean [+ or -] standard error in the descriptive text.

Table 1

Adjusted Post-test Means of Psychological and Physical Measures

 Experimental Group Control Group

Self Concept 21.5 20.7
Self-Efficacy (Upper Body) 9.3 9.2
Self-Efficacy (Lower Body) 9.0 8.8
6 RM Chest Press 29.2 22.0
6 RM Leg Extension 27.9 18.7

Significant F-ratios for experimental versus control groups were noted on chest press strength, F(1, 21) = 18.68, p [less than] .0003 and leg extension strength, F(1, 21) = 14.53, p [less than] .001. Following the training program, the chest press strength of the experimental group increased from 21.4 kg (1.1) to 30.2 k; (1.6) whereas the control group values increased from 18.7 kg (0.6) to 20.4 kg (0.6). Leg extension strength of the experimental group increased from 18.6 kg (1.1) to 28.6 kg (2.1) and control group values increased from 16.4 kg (1.5) to 17.5 kg (1.1). Control group gains are attributable to growth and maturation.

Changes in self-concept, F (1, 21) = 3.25, p = .0859, upper body self-efficacy, F (1, 21) = .03, p = .8673, and lower body self-efficacy, F (1, 21) = .16, p = .6942 were not significant, indicating that there were no differences in the psychological measures between experimental and control groups following the training program. Pre- to post-test changes in self-concept for the experimental and control groups were 20.5 (0.8) to 21.3 (0.7) and 21.1 (0.8) to 21.0 (0.9), respectively. Pre- to post-test changes in upper body self-efficacy scores for the experimental and control groups were 7.6 (0.4) to 9.3 (0.3) and 7.2 (0.5) to 9.3 (0.3), respectively, whereas changes in lower body self-efficacy scores were 7.7 (0.4) to 9.1 (0.3) and 7.3 (0.5) to 8.7 (0.4), respectively.

Discussion

The results of this study indicate that participation in a progressive strength training program will significantly increase the physical strength of boys and girls between the ages of 7 and 12. Observed upper body and lower body strength gains of 53.4% and 41.1%, respectively, are consistent with other short-term training studies involving children (Faigenbaum, Zaichkowsky, Westcott, Micheli, & Fehlandt, 1993; Sewall & Micheli, 1986). No injuries occurred during the strength training program.

Despite significant increases in strength, training did not have a significant effect on psychological measures. These results suggest that a short-term, twice per week strength training program will not significantly effect the perception children have of themselves or their confidence in performance weightlifting activities. However, qualitative statements from children who completed the strength training program suggest the contrary. Children stated that they were more confident in their lifting abilities and were more willing to try different sports and activities following the training program. These children continually commented on their noticeable gains In strength, and at the end of the study their parents remarked on their children's enhanced feelings of well-being.

It is conceivable that the relatively high pretest self-concept scores (ceiling effect) in both the experimental and control groups precluded significant gains. Data from Zaichkowsky et al. (1980) indicate that the mean MZSCS score for fourth grade boys and girls is approximately 17 whereas pretest MZSCS scores for the experimental and control groups in this study were 20.5 and 21.1, respectively. Although speculative, the results of this study suggest that strength training will not enhance the self-concept of children who begin strength training with above average feelings of self-worth.

This argument is consistent with data from Tucker (1983b) who noted an inverse association between pretest measures of self-concept and global self-concept change in adult males who participated in a strength training program. Moreover, a meta-analysis of the relationship between physical fitness and self-concept in children supports the contention that the psychological effect of exercise will be most apparent in children with emotional disturbances (Gruber, 1986).

In the present study, self-efficacy scores increased for both the exercise and control groups indicating that both groups became more confident in their weightlifting abilities. Since self-efficacy involves specific appraisals of personal abilities, a child's perceived ability to lift more weight following eight weeks of strength training was expected. Children in the exercise group gradually increased the resistance as they got stronger, which in turn seemed to enhance their confidence and sense of achievement. Moreover, these children received positive reinforcement from respected fitness instructors and had the opportunity to observe boys and girls their own age weight train.

Yet the control group's increase in self-efficacy was comparable to that of the exercise group. It is possible that positive feedback regarding post-test performances provided the control group with a false sense of accomplishment, thereby engendering self-efficacy improvements not directly related to their self-efficacy gains. Furthermore, unlike adult populations, children are growing and will therefore continually get stronger without specifically training for strength. The control group's increase in growth-related strength may also explain, in part, their enhanced self-efficacy ratings.

Although pilot data regarding youth strength measures were used in the development of the self-efficacy questionnaire, the statements on this form underestimated the experimental group's gain in strength. Thus the experimental group subjects did not have the opportunity to express their confidence in lifting weights over 60 pounds even though the strength tests revealed they had the physical capabilities to do so. For example, 7 children in the exercise group lifted over 60 pounds on the leg extension 6 RM follow-up test (maximum post-test leg extension 6 RM was 91 pounds), whereas the self-efficacy questions regarding lower body strength peaked at 60 pounds. During the administration of the self-efficacy questionnaire, several subjects asked about the purpose of the form and were unsure about assessing their physical capabilities. Although speculative, the cognitive abilities of prepubescent boys and girls, as opposed to older populations, may limit their understanding and appreciation of self-efficacy as it relates to motor skills.

In conclusion, empirical evidence suggests that the potential benefits of youth strength training may include improvements in psychological well-being, though scientific data from this short-term investigation do not support this claim. The self-efficacy questionnaire employed in this study underestimated the observed gains in strength, and children in this study began strength training with relatively high levels of self-concept which may have precluded significant findings. Since this was not a randomized study, the experimental and control groups may have been influenced by some unmeasured characteristics, thus the generalizability of these findings are limited. Longer term randomized trials with larger sample sizes are recommended for future studies.

Author Notes

The authors gratefully acknowledge the staff at the South Shore YMCA, Quincy, Massachusetts, for their technical assistance and support throughout this study.

For further Information, please contact:

Avery D. Faigenbaum Department of Human Performance and Fitness University of Massachusetts 100 Morrissey Boulevard Boston, MA 02125-3393

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