Baum, B.S, & Li L. (2003, April). Lower extremity muscle activities during cycling are influenced by load and frequency. Journal Of Electromyography And Kinesiology: Official Journal Of The International Society Of Electrophysiological Kinesiology, 13(2), 181-190.
The purpose of this experiment was to investigate the effects of frequency and inertia on lower extremity muscle activities during cycling. Electromyographic (EMG) data of seven lower extremity muscles were collected. Sixteen subjects cycled at 250 W across different cadences (60, 80, and 100 rpm) with different loads (0, 0.5, 1.0, 1.5, and 2.0 kg) attached to distal end of their thighs. Load and cadence interactions were observed for the offset of the biceps femoris (BF), the active duration of the rectus femoris (RF), and the peak magnitudes of the vastus lateralis (VL) and the tibialis anterior (TA). Cadence effects were observed in the onset of the gluteus maximus (GM), RF, BF, VL, and TA; the offset of the GM, RF, BF, VL; the duration of the BF and TA; the peak magnitude of the RF and gastrocnemius (GAS); and the crank angle at which the peak magnitude was achieved of the BF, GAS, and soleus (SOL). Load effect was observed from the onset of RF and SOL, the offset of RF, the duration of SOL, and the peak magnitude of BF. These results indicate that inertial properties influence the lower extremity muscular activity in addition to the cadence effect.
Contains some review of muscular vs non-muscular components of pedal force changes.
Seat height was distance between seat and crank center was 100% of subject's greater trochanter length standing.
As pedal cadence increased GM, RF, BF, VL, TA, and SOL had earlier onset of burst timing. GM, RF, BF, and VL had earlier offset of burst timing. BF activity decreased in duration and TA activity increased in duration.
More than 45% of tested variables reacted to the cadence changes. 14% were influenced by the load effect.
Muscles acting on the knee and ankle joints reacted lesser to inertial properties of the leg and foot supporting other similar research findings.
p. 89 "Neptune et al.  hypothesized that EMG muscle burst onset values must shift earlier in the crank cycle as cadences increase in order to develop pedal forces in the same relative area of the crank cycle. Although their results indicated muscle burst onset timing changes, different muscles responded differently to the cadence changes, thus suggesting a coordination change between muscles."
Distinct differences found in ankle musculature reaction to cadence compared to muscles of the hip and knee.
Conclusion, changes in motion speed and inertia of the thigh will affect muscle activity and coordination. Cadence has greater effects proximally than distally for onset, offset, and some antagonist pair coordination. Greater load effects proximally for Peak EMG offset. Mono-articular discrete timing shifts occurred for VL and SOL based on load changes.
Samozino, P., Horvais, N., Hintzy, F. (2007, April). Why does power output decrease at high pedaling rates during sprint cycling?. Medicine And Science In Sports And Exercise, 39(4), 680-687.
PURPOSE: The objective of this study was to partly explain, from electromyographical (EMG) activity, the decrease in power output beyond optimal pedaling rate (PRopt) during sprint cycling. METHODS: Eleven cyclists performed four 8-s nonisokinetic sprints on a cycle ergometer against four randomized friction loads (0.5, twice 0.75, and 0.9 N x kg(-1) of body mass). Power output and EMG activity of both right and left gluteus maximus, rectus femoris, biceps femoris, and vastus lateralis were measured continuously. Individual crank cycles were analyzed. Crank angles corresponding to the beginning and the peak of each downstroke and EMG burst onset and offset crank angles were computed. Moreover, crank angles corresponding to the beginning and the end of muscle force response were determined assuming a 100-ms lag time between the EMG activity and the relevant force response (or electromechanical delay). RESULTS: Muscle coordination (EMG onset and offset) was altered at high pedaling rates. Thus, crank angles corresponding to muscle force response increased significantly with pedaling rate. Consequently, at pedaling rates higher than the optimal pedaling rate, force production of lower-limb extensor muscles was shifted later in the crank cycle. Mechanical data confirmed that downstrokes occurred later in the crank cycle when pedaling rate increased. Hence, force was produced on the pedals during less effective crank cycle sectors of the downstroke and during the beginning of the upstroke. CONCLUSION: During nonisokinetic sprint cycling, the decrease in power output when pedaling rates increased beyond PRopt may be partly explained by suboptimal muscle coordination.
Fig. 1 on p. 682 shows typical EMG shift for electromechanical delay (EMD).
Fig 4 on p. 683 shows typical changes in power output at every point in the pedal stroke for 123 rpm and 170 rpm. Peak power shifts from about 90 to 115 degrees of the pedal stroke on the latter. Thus, power output production is delayed to a higher crank angle when pedaling rate increases. Likewise, the minimum power crank angle increased as pedaling rate increased. Table 1 shows means for different ranges.
Max Power Output
50-90 rpm = 81 degrees crank arm
90-110 = 83
110-130 = 91
Min Power Output
50-90 rpm = 353 degrees crank arm
90-110 = 358
110-130 = 4
Lucia, A., San Juan, A., Montilla, M., Canete, S., Santalla, A., Earnest, C., et al. (2004, June). In professional road cyclists, low pedaling cadences are less efficient. Medicine & Science in Sports & Exercise, 36(6), 1048-1054.
Purpose: To determine the effects of changes in pedaling frequency on the gross efficiency (GE) and other physiological variables (oxygen uptake (VO2), HR, lactate, pH, ventilation, motor unit recruitment estimated by EMG) of professional cyclists while generating high power outputs (PO). Methods: Following a counterbalanced, cross-over design, eight professional cyclists (age (mean +/- SD): 26 +/- 2 yr, VO2max: 74.0 +/- 5.7 mL.kg-1.min-1) performed three 6-min bouts at a fixed PO (mean of 366 +/- 37 W) and at a cadence of 60, 80, and 100 rpm. Results: Values of GE averaged 22.4 +/- 1.7, 23.6 +/- 1.8 and 24.2 +/- 2.0 at 60, 80, and 100 rpm, respectively. Mean GE at 100 rpm was significantly higher than at 60 rpm (P < 0.05). Similarly, mean values of VO2, HR, rates of perceived exertion (RPE), lactate and normalized root-mean square EMG (rms-EMG) in both vastus lateralis and gluteus maximum muscles decreased at increasing cadences. Conclusions: In professional road cyclists riding at high PO, GE/economy improves at increasing pedaling cadences.
Premise of study was the previous studies did not use elite cyclists who are able to generate much higher power outputs. So, the previous research indicating greater VO2 efficiency with lower cadence were not applicable to this population.