1.  strenuous(s = adj.all) - characterized by or performed with much energy or force; "strenuous exercise"
Derived forms noun strain₁₀, noun strenuosity₁, noun strenuousness₁

2.  strenuous(s = adj.all) arduous, straining - taxing to the utmost; testing powers of endurance; "his final, straining burst of speed"; "a strenuous task"; "your willingness after these six arduous days to remain here"
Derived forms noun strain₉, noun strenuousness₁

   Eagerly pressing or urgent; zealous; ardent; earnest; bold; valiant; intrepid; as, a strenuous advocate for national rights; a strenuous reformer; a strenuous defender of his country. [1913 Webster]
"And spirit-stirring wine, that strenuous makes." [1913 Webster]
"Strenuous, continuous labor is pain." [1913 Webster]

strenuous, adj.
1 requiring or using great effort.
2 energetic or unrelaxing.

Derivative:
strenuously adv. strenuousness n.

Etymology:
L strenuus brisk

N  perseverance, continuance, permanence, firmness, constancy, steadiness, singleness of purpose, tenacity of purpose, persistence, plodding, patience, sedulity, pertinacy, pertinacity, pertinaciousness, iteration, bottom, game, pluck, stamina, backbone, grit, indefatigability, indefatigableness, bulldog courage, persevering, constant, steady, steadfast, undeviating, unwavering, unfaltering, unswerving, unflinching, unsleeping, unflagging, undrooping, steady as time, unrelenting, unintermitting, unremitting, plodding, industrious, strenuous, pertinacious, persisting, persistent, solid, sturdy, staunch, stanch, true to oneself, unchangeable, unconquerable, indomitable, game to the last, indefatigable, untiring, unwearied, never tiring, through evil report and good report, through thick and thin, through fire and water, per fas et nefas, without fail, sink or swim, at any price, vogue la galere, never say die, give it the old college try, vestigia nulla retrorsum, aut vincer aut mori, la garde meurt et ne se rend pas, tout vient a temps pour qui sait attendre.

N  activity, briskness, liveliness, animation, life, vivacity, spirit, dash, energy, snap, vim, nimbleness, agility, smartness, quickness, velocity, alacrity, promptitude, despatch, dispatch, expedition, haste, punctuality, eagerness, zeal, ardor, perfervidum aingenium, empressement, earnestness, intentness, abandon, vigor, devotion, exertion, industry, assiduity, assiduousness, sedulity, laboriousness, drudgery, painstaking, diligence, perseverance, indefatigation, habits of business, vigilance, wakefulness, sleeplessness, restlessness, insomnia, pervigilium, insomnium, racketing, movement, bustle, stir, fuss, ado, bother, pottering, fidget, fidgetiness, flurry, officiousness, dabbling, meddling, interference, interposition, intermeddling, tampering with, intrigue, press of business, no sinecure, plenty to do, many irons in the fire, great doings, busy hum of men, battle of life, thick of the action, housewife, busy bee, new brooms, sharp fellow, sharp blade, devotee, enthusiast, zealot, meddler, intermeddler, intriguer, busybody, pickthank, hummer, hustler, live man, rustler, active, brisk, brisk as a lark, brisk as a bee, lively, animated, vivacious, alive, alive and kicking, frisky, spirited, stirring, nimble, nimble as a squirrel, agile, light-footed, nimble-footed, featly, tripping, quick, prompt, yare, instant, ready, alert, spry, sharp, smart, fast, quick as a lamplighter, expeditious, awake, broad awake, go-ahead, live wide-awake, forward, eager, strenuous, zealous, enterprising, in earnest, resolute, industrious, assiduous, diligent, sedulous, notable, painstaking, intent, indefatigable, unwearied, unsleeping, never tired, plodding, hard-working, businesslike, workaday, bustling, restless, restless as a hyena, fussy, fidgety, pottering, busy, busy as hen with one chicken, working, at work, on duty, in harness, up in arms, on one's legs, at call, up and doing, up and stirring, busy, occupied, hard at work, hard at it, up to one's ears in, full of business, busy as a bee, busy as a one-armed paperhanger, meddling, meddlesome, pushing, officious, overofficious, intrigant, astir, stirring, agoing, afoot, on foot, in full swing, eventful, on the alert, actively, with life and spirit, with might and main &c, with haste, with wings, full tilt, in mediis rebus, Int, be alive, look alive, look sharp!, move on, push on!, keep moving!, go ahead!, stir your stumps!, age quod agis!, jaldi!, karo!, step lively!, carpe diem, seize the day, nulla dies sine linea, nec mora nec requies, the plot thickens, No sooner said than done, veni vidi vici, catch a weasel asleep, abends wird der Faule fleissig, dictum ac factum, schwere Arbeit in der Jugend ist sanfte Ruhe im Al, hard work in youth means soft rest in age, the busy hum of men.

N  exertion, effort, strain, tug, pull, stress, throw, stretch, struggle, spell, spurt, spirt, stroke of work, stitch of work, a strong pull a long pull and a pull all together, dead lift, heft, gymnastics, exercise, exercitation, wear and tear, ado, toil and trouble, uphill work, hard work, warm work, harvest time, labor, work, toil, travail, manual labor, sweat of one's brow, swink, drudgery, slavery, fagging, hammering, limae labor, industry, industriousness, operoseness, operosity, trouble, pains, duty, resolution, energy, laboring, laborious, operose, elaborate, strained, toilsome, troublesome, wearisome, uphill, herculean, gymnastic, palestric, hard-working, painstaking, strenuous, energetic, hard at work, on the stretch, laboriously, lustily, pugnis et calcibus, with might and main, with all one's might, with a strong hand, with a sledge hammer, with much ado, to the best of one's abilities, totis viribus, vi et armis, manibus pedibusque, tooth and nail, unguibus et rostro, hammer and tongs, heart and soul, through thick and thin, by the sweat of one's brow, suo Marte, aide-toi le ciel t'aidera, and still be doing, never done, buen principio la mitad es hecha, cosa ben fatta e' fatta due volie, it is better to wear out than to rust out, labor omnia vincit, labor, wide as the earth, has its summit in Heaven, le travail du corps delivre des peines de l'esprit, manu forti, ora et labora.