Enriss said:
I'll assume it's implied that you've never seen a study showing that cross training improves cycling performance.
Do you know of any studies that show cross training decreases performance?
Check out a few of these. Some odd 'intereference effect' is mentioned often when they study strength + enduro training at the same time.
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The Interference Effects of Training for Strength and Endurance Simultaneously
Hennessy, Liam C.; Watson, Anthony W.S.
Abstract
This study compared the effects of three preseason training programs on endurance, strength, power, and speed. Subjects were divided into four groups: the endurance (E) group completed a running endurance program 4 days [middle dot] week-1; the strength (S) group trained 3 days [middle dot] week-1; the S+E group combined S and E training programs 5 days [middle dot] week-1; the control (C) group did not train. After 8 weeks, the E and S+E groups had similar gains in endurance running performance, the S group had no change, while the C group showed a decline. No strength gains were noted in the C or E groups, but strength gains were made in the S+E and S groups. Power (vertical jump performance) and speed (20-m sprint time) gains were noted only for the S group. These findings show that training for strength alone results in gains in strength, power, and speed while maintaining endurance. S+E training, while producing gains in endurance and upper body strength, compromises gains in lower body strength and does not improve power or speed.
(C) 1994 National Strength and Conditioning Association
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Eur J Appl Physiol. 2003 Mar;89(1):42-52. Epub 2002 Dec 14.
Neuromuscular adaptations during concurrent strength and endurance training versus strength training.
Häkkinen K,
Alen M,
Kraemer WJ,
Gorostiaga E,
Izquierdo M,
Rusko H,
Mikkola J,
Häkkinen A,
Valkeinen H,
Kaarakainen E,
Romu S,
Erola V,
Ahtiainen J,
Paavolainen L.
Neuromuscular Research Center, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland.
[email protected]
The purpose of this study was to investigate effects of concurrent strength and endurance training (SE) (2 plus 2 days a week) versus strength training only (S) (2 days a week) in men [SE: n=11; 38 (5) years, S: n=16; 37 (5) years] over a training period of 21 weeks. The resistance training program addressed both maximal and explosive strength components. EMG, maximal isometric force, 1 RM strength, and rate of force development (RFD) of the leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris (QF) throughout the lengths of 4/15-12/15 (L(f)) of the femur, muscle fibre proportion and areas of types I, IIa, and IIb of the vastus lateralis (VL), and maximal oxygen uptake (VO(2max)) were evaluated. No changes occurred in strength during the 1-week control period, while after the 21-week training period increases of 21% (p<0.001) and 22% (p<0.001), and of 22% (p<0.001) and 21% (p<0.001) took place in the 1RM load and maximal isometric force in S and SE, respectively. Increases of 26% (p<0.05) and 29% (p<0.001) occurred in the maximum iEMG of the VL in S and SE, respectively. The CSA of the QF increased throughout the length of the QF (from 4/15 to 12/15 L(f)) both in S (p<0.05-0.001) and SE (p<0.01-0.001). The mean fibre areas of types I, IIa and IIb increased after the training both in S (p<0.05 and 0.01) and SE (p<0.05 and p<0.01). S showed an increase in RFD (p<0.01), while no change occurred in SE. The average iEMG of the VL during the first 500 ms of the rapid isometric action increased (p<0.05-0.001) only in S. VO(2max) increased by 18.5% (p<0.001) in SE. The present data do not support the concept of the universal nature of the interference effect in strength development and muscle hypertrophy when strength training is performed concurrently with endurance training, and the training volume is diluted by a longer period of time with a low frequency of training. However, the present results suggest that even the low-frequency concurrent strength and endurance training leads to interference in explosive strength development mediated in part by the limitations of rapid voluntary neural activation of the trained muscles.
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Lots more if you have access to the pub med website. I can only see the summaries.