2019 Comparison of changes in lean body mass with a strength versus copia
This 2019 randomized controlled trial examined whether an 8‑week resistance‑training (RT) program emphasizing muscular strength (3 sets × 6‑8 RM, 3‑min rest) or muscular endurance (3 sets × 20‑25 RM, 1‑min rest) would differentially affect body‑composition outcomes in 25 resistance‑trained men who followed a supervised hyper‑energetic diet (39 kcal·kg⁻¹·day⁻¹, 2 g·kg⁻¹·day⁻¹ protein). Participants were allocated to a strength‑type RT group (n = 10), an endurance‑type RT group (n = 10), or a control group (n = 5). Training sessions were supervised, performed to volitional failure, and included systematic manipulation of load, repetitions, rest intervals, exercise order, and cadence to maximize either mechanical tension (strength) or metabolic stress (endurance). Body composition (total body mass, fat mass, lean body mass) was assessed pre‑ and post‑intervention using dual‑energy X‑ray absorptiometry (DXA). Statistical analysis employed repeated‑measures GLM, ANOVA, and effect‑size calculations. Results showed a significant within‑group increase in total body mass (+0.9 kg) and lean body mass (+1.3 kg) only in the strength‑type group; fat‑mass changes were non‑significant across groups. No significant between‑group interactions were observed for any outcome, and effect sizes were small to moderate. The discussion contextualizes these findings with prior literature, noting inconsistencies, the possible influence of rest‑interval length, and the large inter‑individual variability among trained subjects. Limitations include the short duration (8 weeks), small sample size, lack of site‑specific hypertrophy measures, and absence of acute hormonal or molecular markers. The authors conclude that while strength‑focused RT yields modest absolute gains in lean mass, the practical significance is limited, and combined heavy‑light protocols may be more effective for hypertrophy.
Topics
Study Rationale and Hypothesis: Strength vs. Endurance RT for Hypertrophy
The authors frame the investigation around the theory that manipulating RT variables to emphasize mechanical tension (strength) or metabolic stress (endurance) may differentially drive lean mass accretion in trained individuals.
Participant Profile and Randomized Design
Twenty‑five resistance‑trained men (average age 28 y, >2 y training history) were randomly assigned to strength‑type RT, endurance‑type RT, or control, with detailed inclusion/exclusion criteria and ethical approval.
Training Protocols: Manipulating Load, Reps, Rest, Order, and Cadence
Comprehensive description of the two experimental RT programs—strength (6‑8 RM, 3 min rest, alternating push/pull order) versus endurance (20‑25 RM, 1 min rest, serial muscle‑group order)—including progression rules and supervision to failure.
Nutritional Control: Hyper‑energetic, Protein‑rich Diet
All participants in the experimental groups followed an individualized diet delivering 39 kcal·kg⁻¹·day⁻¹ with 2 g·kg⁻¹·day⁻¹ protein, monitored via MyFitnessPal and overseen by a sports‑nutrition specialist.
Body‑Composition Assessment via DXA
Pre‑ and post‑intervention whole‑body lean mass, fat mass, and total mass were measured using a calibrated Hologic QDR 4500 DXA scanner, with standard positioning and daily quality checks.
Statistical Analyses and Effect‑Size Reporting
Repeated‑measures GLM, ANOVA with Bonferroni correction, partial eta‑squared, and Cohen’s d were employed to evaluate time, group, and interaction effects, with significance set at p < 0.05.
Key Findings: Modest Lean‑Mass Gains in Strength‑type RT Only
Strength‑type RT produced a significant within‑group increase in lean body mass (+1.3 kg, ES = 0.31) and total body mass (+0.9 kg, ES < 0.2); endurance‑type RT showed no significant changes, and no between‑group differences were detected.
Interpretation, Limitations, and Future Directions
The discussion relates results to prior mixed findings, attributes possible attenuation in the endurance group to short rest intervals, acknowledges high inter‑individual variability, and cites limitations (short duration, small N, lack of site‑specific hypertrophy measures, no hormonal markers).