- Click here for explanation of classification scheme.

To review the effects of aerobic exercise training (AET) on blood lipids and assess dose-response relationships and diet interactions.

1. Does the available evidence support the hypothesis that endurance exercise training has a favorable influence on the blood lipid profile relative to future risk of CHD?
2. Does blood lipid responses to training differ by study subjects' sex, age, or race, baseline lipid levels, and baseline relative body wt & its change w/ training?
3. Are lipid responses to exercise related to intensity, duration, weekly volume of energy expenditure, length of endurance program, & associated changes w/ training in VO2 max?

Studies published on or after 1987

Studies in English language

Greater than 12 week endurance program

*consisted of supervised structured group aerobic exercise programs in sedentary, apparently healthy, white individuals, unless indicated.

*Few studies w/ monitored "lifestyle activities" &/or home exercises.

*A few with resistance training

Studies before 1987

Less than 12 week endurance exercise program

Studies not of English language

Recruitment - English literature search using Medline & Index Medicus using key words (physical activity, blood lipids, lipoproteins, alone or in combination) for studies published later than or in 1987;  Additional studies used that were published before 1987 came from references by predious reviewers.

Design - Meta-analysis

 

Blinding used (if applicable)- N/A

 

Intervention (if applicable)- N/A

 

Statistical Analysis- Pearson correlation, stepwise multiple linear regression two-tailed t-test

Timing of Measurements- Before exercise program and after exercise program

Dependent Variables- % change from before to after training in lipid parameters

Independent Variables- baseline age, sex, TC, LDL-C, HDL-C, TG, BMI, VO2 max, previous medical Hx (ex:  one study contained men w/ HTN); KJ/week of exercise performed, changes after training in body wt, VO2 max, blood lipids

Control Variables

Training program:

1. type of activity: (walking, jogging, swimming, cycle ergometer, stairclimber, rowing machine, strength training, dancing, circuit training, ball games, ski machine, step aerobics) 
2. length of the program 
3. intensity (almost all studies it was moderate to hard), frequency (in almost all it was 3-5 times/week >30 mins), 
4. duration of sessions (12 weeks to 2 years) 

Initial N: 51 studies (28 randomized control)    

Attrition (final N): supposedly 51, however, only 44 are in Table 3 (it summarizes each study); 4700 participants 

Age: men aged 17-80 and women aged 17-80 per tables (text states 18-80 with a mean age of 46.6 + or - 0.35);

Ethnicity: majority white, text states 2 studies included African-Americans, however table indicates 3 studies included African Americans (Duncan et al, 1991; Leon et al, 2000; Kokkinos et al, 1998), text states 0 hispanics as subjects however tables indicate 1 study included Hispanics (Duncan et al, 1991), 2 studies with Japanese individuals (Sunami et al, 1999; Motoyama et al, 1995) 

Other relevant demographics: premenopausal women, postmenopausal  women {Cauley et al, 1987 (203 subjects); Lindheim et al, 1994 (95 subjetcs); Klenbanoff et al, 1998 (18 subjects); Fox et al, 1996 (40 subjects)}, 1 study included subjects with antihypertensive meds (Kokkinos et al, 1998) 

Anthropometrics: BMI categories- < 25 (10 studies), 25-29.9 (25 studies), >30 (9 studies); Mean baseline lipid levels- TC 204.5 + 33.9 mg/dL, LDL 136.5 + 22.5 mg/dL, HDL 45.6 + 9.3 mg/dL, TG 125 + 27.8 mg/dL

Location: Researchers from University of Minnesota

 

Table 5:Correlations of baseline and posttraining variables with changes in blood lipids (N=61 study groups involving about 2200 participants)                                

                                     Percent changes w/ Taining

Variable            Total Cholesterol        LDL        HDL        TG

Pretraining

age (yr)                    -0.219                -0.183        -0.038    -0.154

weight (kg)               -0.110                -0.124        0.182     -0.439**

BMI (kg/m2)              -0.006                -0.013        0.130     -0.313*

VO2 max                   -0.216                -0.249        0.103      -0.439**

TC                             -0.269                -0.094        0.024      -0.077

LDL                           -0.420**            -0.232        -0.067      -0.065

HDL                           -0.148                 0.027        -0.462**   0.348*

TG                            -0.297                 -0.139          0.164     -0.290*

Wks of training        -0.137                  -0.330*      -0.073       0.081

Exercise volume        0.205                  -0.045         0.078       -0.097

Posttraining

Weight loss (kg)        0.415**                0.381**   -0.227        0.443**

change VO2 max (%) 0.027                    0.196        0.222       -0.084

change TC                  1.00                      0.800**   -0.154        0.550**

change LDL                0.800**                 1.00         -0.402**    0.128

change HDL              -0.154                    -0.233*        1.00        -0.069

change TG                  0.550**                 0.128         -0.175       1.0

*P<0.05, **P<0.01

(analysis was limited to groups which performed exercise without concomitant dietary changes)

1)Significant inverse assoc found b/w the change in HDL with training and baseline HDL (r= -0.462).  This association was even stronger in studies reporting significant increases in HDL with training (r= -0.676)

2)Significant association with increased HDL with a change in LDL w/ training (r= -0.402)

3)All lipid parameters generally improved in studies in which there was a substantial weight loss (>a4 kg), usually associated with a concomitant hypocaloric diet

 

Per question #1 in purpose:  The bulk of the evidence supports the hypothesis that endurance exercise training in both RCT and non-RCT, despite great inconsistencies.  Exercise training also appears to attenuate the reduction in HDL accompanying a decreased dietary intake of sat fat and cholesterol to promote reduction of LDL.

Per question #2 in purpose:  Adult men & women appear to respond similarly to training.  Age doesn't appear to be a predictor of lipid responsiveness to training.  There is limited data on racial and ethnic differences.  Baseline body wt was found to be inversely related to change in TG; Studies in which a sizable wt loss was obtained while holding the percent of energy intake constant generally had a favorable effect on the entire lipid/lipoprotein profile; however a concomitant reduction in percent energy from fat clearly reduces the HDL response to exercise.  Baseline lipid levels appear to strongly influence the lipid response to training.

Per question #3 in purpose:  Insufficient data to conclusively establish a dose-response relationship b/w intensity and volume of exercise and lipid responses.  Most of the reviewed studies showing HDL changes used an exercise prescription w/ moderate- to hard-intensity activities for at least 30 minutes, three times per week (can raise HDL).  No significant correlation was found b/w the increas in VO2 max and change in HDL with training

Government:	NHLBI,
University/Hospital:	University of Minnesota Heart Disease Prevention Clinic, Universidad de Oriente (Venezuela)

This review indicated the specific flaws of the various studies.  The reviewer also listed 8 recommended study topics to improve current studies.

The problem with generalizing these articles is that they pertain to mostly healthy, white individuals. 

Inclusion criteria indicated it used articles published >1987, however, additional studies published <1987 were used  if they were identified  by previous reviewers.

This analysis never explicitly stated what the exclusion criteria were.  It was abstracted from the reading.

I think they should have discussed more in depth their findings when diet and exercise were combined.  Indicate what was significant or not.

This analysis seemed to focus on HDL changes.  I feel that all lipid parameters should have been discussed in more depth.  They didn't discuss the significant changes (or p-value) revealed with the other lipid parameters